text:
Why is schizophrenia a thought disorder and bipolar a mood disorder?
Examining two major mental illnesses that are,  loosely, grouped by mood and thought.
Schizophrenia is regarded as an illness associated with thought disorder.
Bipolar is regarded as a mood disorder.
Both conditions can lead to a psychotic break and behavioral disturbance. Hallucinations can occur in both.
Bipolar is characterized by depression with the occurrence of, at least, one episode of mania.
Schizophrenia is characterized by phases. An active phase, where psychotic symptoms peak and the negative phase, when the personality has little affect.
Given that both cause behavioral problems and changes to mood. That psychosis is based on false beliefs, and beliefs are thoughts. What is the scientific and the psychiatric basis for regarding schizophrenia as a thought disorder and bipolar a mood disorder?

Bipolar is regarded as a mood disorder. - Depends on whom you ask.  What defines a mood disorder?  What defines a thought disorder?  What defines an illness?  In all honesty, I don't think this is answerable given the current state of psychiatric science, but I'd be happy to be proven wrong...

To clarify, the difference would, semantically-speaking, be that one regards maladaptive thoughts while the other concerns maladaptive emotions.  But where's the barrier between those two?  Where's the barrier between those and physical/neurological 'illness'?  French (and lots of European) psychiatry takes a psycho-behavior/lifestyle approach to addressing these issues, while in the US there's a much stronger pharmaceutical approach.

@BenCole: the question is nevertheless quite reasonable because distinction is made in the "psychiatric bible" aka the DSM.

The simple answer is that bipolar disorder can occur without psychosis. The paper that opens the other answer is titled "Differences in resting-state functional magnetic resonance imaging functional network connectivity between schizophrenia and psychotic bipolar probands and their unaffected first-degree relatives." (Emphasis mine.)
You can also have (unipolar) depression with psychotic symptoms. And its status is (and has been) equally iffy:

There has been a long-standing discussion as to whether psychotic depression is a distinct syndrome or simply represents a severe form of depression. Much of the debate stems from the fact that in DSM-II, published in 1968, “psychosis” meant severe and did not mean being out of touch with reality or having delusions or hallucinations. In 1970, Gerald Klerman and Eugene Paykel published an influential article that stated that in depression, there was a smooth continuum from mild outpatient depression to severe depression requiring inpatient hospitalization without any demarcation points. Observations that psychotic depressed patients differed from nonpsychotic patients in their response to pharmacological treatments led investigators to focus on more clearly defining this distinct clinical entity.
In 1992, as Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV was being planned, a strong argument was made in the American Journal of Psychiatry that there was sufficient evidence at that time from studies of clinical characteristics and symptoms, biology, family history, course and outcome, and treatment that psychotic depression should be a distinct illness in DSM-IV, separate from major depression. The American Journal of Psychiatry article led to a position paper submitted to the DSM-IV Work Group on mood disorders. The DSM-IV Work Group on mood disorders agreed that the clinical relevance of specifically designating patients with psychotic depression was high and considered 2 options: (1) to continue the classification as in DSM-IIIR designating psychosis as decimal point under the severity code and (2) to designate psychotic depression as a separate syndrome “major depression with psychotic features.” After much deliberation, the work group recommended the first option although it recognized it was less than optimal. Thus, in DSM-IV and DSM-IV text revision, psychotic depression remained as a subclassification of major depressive disorder.
Similarly, in the International Classification of Diseases, 10th revision (ICD-10), psychotic depression is classified as a subtype of severe depression. Arguments that psychotic depression meets the criteria for a valid psychiatric syndrome due to its distinct clinical presentation, neurobiology, heritability, prognosis, and treatment response continue to be made with the hope that this will change in ICD-11.
In DSM-V, psychotic depression will remain as a subclassification of major depressive disorder. However, in DSM-V, psychotic features will be separated from the severity rating, and major depressive disorder with psychotic features will not necessarily need to be classified as “severe.” This is a change from DSM-IV. Moreover, in DSM-V, a hierarchy giving precedence to mood-incongruent features is being introduced to allow classification of cases in which mood-congruent and mood-incongruent psychotic features coexist.

Sorry for the rather long quote, but I cannot summarize the controversy of psychotic depression in much less than that.
And to get back to bipolar, DSM-5 split the mood section (one chapter in DSM-IV) into two Depressive and Related Disorders and Bipolar and Related Disorders. They actually located Bipolar in-between Depressive and Schizophrenia Spectrum and Related Disorders

in recognition of their place as a bridge between the two diagnostic classes in terms of symptomatology, family history and genetics

(DSM-5, p. 123)
And if you wonder why this progression, here's some correlational epidemiology

A diagnosis of BPI [bipolar I] disorder was strongly predictive of psychotic features during depression compared to MDDR [major depressive disorder] (odds ratio [OR] = 4.61, p < 0.0005). Having bipolar II compared to MDDR was not predictive of psychosis (OR = 1.05, p = 0.260), nor was having a family history of BPI in MDDR subjects (OR = 1.20, p = 0.840).

And one interesting thing is that in practice, the presence of psychosis makes the diagnosing psychiatrist significantly depart from the DSM:

However, the question of where to place psychotic symptoms within the framework of clinical diagnosis is still confusing. Meyer and Meyer (2009) sought to examine this issue using identical vignettes of a clinical presentation adjusted only for the presence of auditory hallucinations (more commonly associated with psychotic disorders) and the decreased need for sleep (one possible symptom of mania) to evaluate how actual psychiatrists would diagnosis and what subsequent treatment they would recommend. Although the vignette was written to clearly present a patient with mania warranting a diagnosis of Bipolar Disorder (DSM-IV criteria), almost half of the psychiatrists gave an inappropriate diagnosis (45% total; 41.5% psychotic disorder, 3.5% other diagnosis), with a manic episode diagnosed by 37.3% of the psychiatrists and bipolar affective disorder diagnosed by 16.9% of the psychiatrists

as noted in "Historical Underpinnings of Bipolar Disorder Diagnostic Criteria
" which is actually a very good read for the historical basis of the distinction (it started with the Kraepelian dichotomy), much more than I can hope to convey here.
What I will say is that the blurring distinction that the DSM-5 sorta acknowledged has been proposed much more vigorously by some researchers. In particular, Craddock "going" paper was one of my favorite papers some years ago, proposing an even more daring overlap, with cognitive issues of schizophrenia overlapping autism.

Alas, the quest for biomarkers in psychiatry is still in its infancy.
Also, while the DSM (IV) clearly defined bipolar as a mood disorder, they don't say that schizophrenia is a thought disorder, so I'm not sure what you based that on. Science Direct has a page with a lot definitions of schizophrenia excerpted from (recent) books, and none define it a thought disorder although one (Sontheimer) does say that it is

a collection of symptoms that are dominated by psychosis. However, symptoms also include deficits in thinking, behavior, and affect [...]".

Another (Benson) says

its defining symptoms are typically delusions and hallucinations in the absence of extreme emotion. Cognitive impairment or thought disorder is also considered a cardinal symptom.

On the other hand, the NHS does have a page on which it equates psychosis with thought disorder in the title. I guess the specialists don't consider the concepts synonymous, but for the general public... some let that slide.

In this paper, the authors note that bipolar disorder and schizophrenia share many abnormal resting state network connections. But some connections are specific to bipolar disorder and others are specific to schizophrenia.
I think to really describe the two illnesses, one must look at specific biological data. Fuzzy terms like "mood disorder" and "thought disorder" are used without any concrete meaning. If somebody looked at the fmri data he would be able to tell the difference between bipolar disorder and schizophrenia (without knowing any psychiatric terms). At the same time, I think looking solely at fmri data can be too abstract without being informed by psychology and psychiatry. A good book on this subject is Brainwashed: The Seductive Appeal of Mindless Neuroscience.
There is also some evidence that time perception may be altered in various mental illnesses. So one may distinguish bipolar disorder and schizophrenia in terms of differences of time perception.
Source
Differences in resting-state functional magnetic resonance imaging functional network connectivity between schizophrenia and psychotic bipolar probands and their unaffected first-degree relatives.
Meda SA, Gill A, Stevens MC, Lorenzoni RP, Glahn DC, Calhoun VD, Sweeney JA, Tamminga CA, Keshavan MS, Thaker G, Pearlson GD.


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What personality traits moderate the effects of trauma on empathy?
Logically there are three ways trauma can affect a person's propensity for empathy.

increase
decrease
no change

What are the key personality traits that can be used as predictors of this outcome?

There is a large and diverse literature on this topic which paints a complex picture of the relationship between trauma and empathy.
Some studies have found significant trauma symptoms to be related to less empathy. A study of Israeli children who had experienced the trauma of Arab missile attacks found that 66% of children with very negative attitudes towards Arabs had severe posttraumatic symptoms, while none of the children who expressed balanced attitudes towards Arabs had severe posttraumatic symptoms (Laor, Wolmer, & Cohen, 2004). Children with balanced attitudes also exhibited more prosocial behavior, offering to donate 35% more candy to ill peers than children with more negative attitudes. Overall, the authors found that those with very negative attitudes were less able to regulate their behavior, had poorer defense mechanisms, and had more externalizing and PTSD symptoms, while children with balanced attitudes were older and had fewer symptoms and more positive defenses. Thus, while children with better coping styles had both fewer trauma symptoms and were more empathetic/generous, is not possible to determine the direction of these relationships in this study. Also, the coping styles and attitudes of these child could be highly influenced by the environment (i.e., their parents’ behavior and attitudes).
A study of college students found that over 26% reported significant PTSD symptoms and 29-58% various forms of psychological distress following the 9/11 attacks, despite having no personal connection to the event (Woodward, Murrell, & Bettler, 2005). The study also found that a person’s level of empathy was positively correlated with the amount of traumatic stress symptoms they reported; perhaps not surprising, as you might need a certain level of empathy to experience someone else’s trauma so acutely. Additionally, while traumatic stress symptoms were positively correlated with the amount of psychological distress the person was experiencing, empathy was negatively correlated with psychological stress, both directly and via the person’s interpersonal style. That is, those individuals with more empathy and with positive interpersonal styles (a combination of coping skills, attachment, and social support), had better psychological functioning in the face of trauma.
Other studies have found that trauma may impact empathy in different ways, depending on the type of trauma. One study suggests that trauma which is directed at the self (abuse or severe illness) may not stimulate empathy for the self, resulting in negative psychological  outcomes, but that trauma directed at another (losing a loved one, witnessing injury/abuse of a loved one) may stimulate empathy to help the other person (Keinan, Shrira, & Shmotkin, 2012). Thus, even if the person experiences an event as traumatic, the motivation to help the victim (or others who care about the victim) may result in surges of empathy.
Another study found that only certain types of empathy were impacted by trauma (Nietisbach, Maercker, Rossler, & Haker, 2010). When these authors compared individuals with PTSD to those without PTSD, they found that both groups had similar levels of the complex empathic skills such as social cognition (i.e., being able to recognize faux pas or take the perspective of others), but individuals with PTSD symptoms were less likely to demonstrate more basic empathic skills such as “empathic contagion,” yawning or laughing when seeing someone else yawn or laugh. The authors also noted that individuals with PTSD for whom more time had passed since their trauma had a greater ability to take the perspective of others compared to individuals with PTSD who were closer to their time of trauma; this may indicate a change in empathic ability over time. Finally, they found that both individuals with PTSD and those without PTSD reported similar self-reported levels of empathy for others, but that those with PTSD reported greater distress when faced with the difficulties of others. The authors hypothesized that individuals with PTSD may be consciously avoiding empathic contagion due to this heightened experience of distress when watching others struggle, meaning part of the empathic deficit may actually be a defense mechanism.
A study of veterans with PTSD found that those who lacked empathy were more likely to be verbally, but not physically or impulsively, aggressive (Teten, Miller, Bailey, Dunn, & Kent, 2008). However, those veterans who also experienced alexithymia, meaning they are unable to name or describe their emotions with words, were more likely to be impulsively aggressive; a lack of empathy was not significantly associated with impulsive aggression. So, when considering aggressive behavior and trauma, it may be important to recognize that not all negative behavior is necessarily due to trauma’s impact on empathy.
Other studies have focused on the role of trauma in increasing empathy or helping behavior. One study found that individuals with greater numbers of lifetime traumatic events had greater self-reported empathy and volunteering behavior than those with fewer traumatic events (Frazier et al., 2013). However, this study was unable to conclude whether trauma had led to increases in empathy and whether such an increase was the reason for the increased prosocial behavior. Staub and Vollhardt (2008) have suggested that there are a specific set of experiences that may promote “altruism born of suffering” (i.e., increased empathy in reaction to trauma). Specifically, they propose if individuals who experience a traumatic event then experience psychological healing, social support, positive self-action, and altruistic role models, they may experience a range of post-traumatic growth including increased empathy and prosocial behavior. Staub and Vollhardt (2008) do note as others authors have that empathizing with other people’s distress can cause distress and possibly decrease empathy unless sufficient coping mechanisms are in place. A 2009 paper reviews recent evidence for this concept, and emphasizes the need for a better understanding of the experiences which lead to altruism following trauma, rather than suffering or revenge (Vollhardt, 2009).
In sum, trauma can impact empathy and prosocial behavior in a variety of ways, depending on individual characteristics and context. The links below should provide you a starting point to find additional resources on this topic. While most of the literature focuses on the impact of trauma on adults with “normal” empathic responses prior to the trauma, Music (2012) provides a theoretical argument that the development and acquisition of empathy may not occur properly when children are subjected to significant abuse or neglect. His paper may be a good reference if you’re interested not only in how trauma impacts existing capacity for empathy, but in how it impacts the development of empathy.
Frazier, P., Greer, C., Gabrielsen, S., Tennen, H., Park, C., & Tomich, P. (2013). The relation between trauma exposure and prosocial behavior. Psychological Trauma: Theory, Research, Practice, and Policy, 5(3), 286-294. DOI: 10.1037/a0027255.
Keinan, G, Shrira, A., & Shmotkin, D. (2012). The association between cumulative adversity and mental health: considering dose and primary focus of adversity. Quality of Life Research, 21, 1149-1158.
Laor, N., Wolmer, L., & Cohen, D. J. (2004). Attitudes toward Arabs of Israeli children exposed to missile attacks: The role of personality functions. The Israel Journal of Psychiatry and Related Sciences, 41(1), 23-32.
Music, G. (2012). Selfless genes, altruism, and trauma: Research and clinical implications. British Journal of Psychotherapy, 28(2), 154-171. DOI: 10.1111/j.1752-0118.2012.01276.x
Nietlisbach, G., Maercker, A., Rossler, W., & Haker, H. (2010). Are empathic abilities impaired in posttraumatic stress disorder? Psychological Reports, 106(3), 832-844. DOI: 10.2466/PR0.106.3.832-844
Staub, E., & Vollhardt, J. (2008). Altruism born of suffering: The roots of caring and helping after victimization and other trauma. American Journal of Orthopsychiatry, 78(3), 267-280. DOI: 10.1037/a0014223
Teten, A. L., Miller, L. A., Bailey, S. D., Dunn, N. J., & Kent, T. A. (2008). Empathic deficits and alexithymia in trauma-related impulsive aggression. Behavioral Sciences and the Law, 26, 823-832. DOI: 10.1002/bsl.843
Vollhardt, J. (2009). Altruism born of suffering and prosocial behavior following adverse life events: A review and conceptualization. Social Justice Research, 22, 53-97. DOI: 10.1007/s11211-009-0088-1
Woodward, L. E., Murrell, S. A., & Bettler, R. F. (2005). Empathy and interpersonal style: A mediational model of secondary traumatic stress symptomology following 9/11. Journal of Aggression, Maltreatment, & Trauma, 11(4), 1-28. DOI: 10.1300/J146v11n04_01

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The Dark Triad Abnormal Development or Base Human Nature?
I propose the concept, that human beings, as animals have the same instincts as other animals. Even though we are social animals, we still have the basic nature of fight and flight and we teach ourselves to overrule these with the "conscious mind" or frontal lobe. To help reinforce the practice of inhibiting behaviour that "may" be destructive to other human beings, are many laws, and  social and organisational constructs of "morality" (eg religion, schooling). These practices assist in the individuals development of conscience.
This leads me to a group of people who fail to conform to the social norms that are supposed to help to  ensure that human beings have the optimal chance to overcome base desires and instincts.
The Dark Triad;
Narcissism
Machiavellianism
Psychopathy
The key features being;
lack of empathy
self-centredness
lack of remorse
From the pure analysis that the percentage of people with these diagnoses are not the norm. It can be argued that these people are defective, as they are not the norm. It has been argued these personality types can be genetic and caused by environment and every permutation between. One could, almost argue that it is the underlying "default" of human nature, when all our conditioning is stripped away.
My question is:
Are people diagnosed with Narcissism, Machiavellianism or Psychopathy  truly different; or are these set of personality traits dormant within all people?

The Dark Triad traits you speak of are subclinical personality traits, therefore they cannot be diagnosed. Everyone carries some of the characteristics of these traits. People high on these traits are also not considered to be defective, even better they may in some environments be considered to be an advantage (e.g., business areas).
You may want to read up on research on the Dark Triad, mainly that by Dr. P. K. Jonason. He is one of the main contributors to the Dark Triad research and uses an evolutionary paradigm to discuss his research, showing how the Dark Triad may be adaptive.

It is adaptive, to a world we would not want.

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Is the 'addiction' to receiving sympathy similar to substance addiction or just a deficit of resilience?
A lot have encountered people who seem to be addicted to receiving sympathy - before getting to my question, allow me to clarify, what I am referring to are people for whom, knowingly portray 'everything as a crisis'.  I am deliberately putting 'addiction' in quotation marks as I am not sure that it is in fact an addiction.
I used to be this way myself, making even the smallest transgression into a big issue and then using it to get sympathy from others, when I received said sympathy - it felt 'good'.  (Nowadays, I just deal with issues myself).
So, my question is, is the sympathy 'addiction' akin to substance addiction or is it a deficit of resilience? or maybe both?

Are you refering to the psychological concept of resilience as used e.g. in this article?

@JensKouros yes, that is pretty well where I am looking.  Great link!

Relevant? - Munchausen syndrome

There is a correlation between those who seek sympathy and those with substance abuse issues. I see many examples of it in both my personal and professional life. Drug and alcohol Abuser's all seem to share a common trait, they often or usually also seek sympathy both during relapses and during sobriety. So I would say sympathy and substance addiction go hand in hand.

Is "sympathy" the right word here? Aren't such personality type only seeking attention of any kind, though they would prefer "positive" attention that makes them feel good?

This is a part answer, which only refers to the concept of resilience.
One of the first studies that invesigated resilience was the Kauai-Study, which was a longitudinal study of a cohort in Hawai to investigate the cognitive, social and physical development of children. (Werner and Smith, 1982) Of the children who had to deal with a couple of risk factors from birth on, about a third managed to overcome the obstacles later in life. This led to the formulation of a theoretical concept of resilience, which included vulnerability of the child as a main risk factor and external stress on one side, and social support and ressources within the child on the other side as elements. These elements interact with one another and influence the development of a child. In this sense, resilience was defined as a potential, or maybe kind of like a trait. If there is enough resilience, a "good" development will be possible in spite of a difficult environment. The second thing to notice is that resilience originally was geared towards children.
The concept of resilience has been expanded to adulthood later. Apparently, though, this has led to some problems concerning the definition, since the original conception was explicitly concerned with development in childhood (Luthar and Cicchetti, 2000). The article of Leipold and Greve (2009) integrates different proposals to solve this problem. In their model, resilience, development and coping are linked. Development is seen as coping with all kinds of demands and stressors, and resilience is seen as succesfully doing so. Note that in this definition, resilience is very different from the one that I have given above.
To get to your question: an "addiction to sympathy" might be seen as a lack of resilience, but not in the sense of a trait. It can be seen as the lack of a process as conceptualized by Leipold and Greve (2009). This also leaves open the possibility that the process might "kick in" at a later stage in development, which not only makes sense but is also what you have experienced yourself.
References:

Leipold, B. & Greve, W. (2009). Resilience. A conceptual bridge between coping and development. European Psychologist, 14, 40-50.
Luthar, S. S., & Cicchetti, D. (2000). The construct of resilience: Implications for interventions and social policies. Development and psychopathology, 12(4), 857-885.
Werner, E. E. & Smith, R. S. (1982). Vulnerable but invincible: A study of resilient children New York: McGraw-Hill.

This is perfect, as it explains my own experience pretty much precisely.  Great answer.

1) I don't believe a person can be addicted to gaining sympathy. I believe that a person who is in the habit of manipulating others for sympathy is more a reflection of a deficit within their personality, as opposed to an addiction.
The  one exception being within a Histrionic Personality Disorder or the like, where a person becomes addicted to the chemical release in the brain that comes with high stress and drama. I regard the focus here is on create crises as opposed to seeking sympathy.
2) As for a lack of resilience, the character weakness may or may not be linked to a low level of resilience. There are many variables that would need to be examined before passing that judgment.
The seeking of sympathy can be a part of attention seeking behaviours, which in turn can be a part of a personality disorder. It would be fair to say that the complexity of personality disorders, could not be summed up in terms of resilience. Although it can be said, that a person lacking healthy coping skills, may be less resilient.

The American Psychological Association suggests "10 Ways to Build
  Resilience", which are:

maintaining good relationships with close family members, friends
  and others;
to avoid seeing crises or stressful events as unbearable problems;
to accept circumstances that cannot be changed;
to develop realistic goals and move towards them;
to take decisive actions in adverse situations;
to look for opportunities of self-discovery after a struggle with
  loss;
developing self-confidence;
to keep a long-term perspective and consider the stressful event in
  a broader context;
to maintain a hopeful outlook, expecting good things and visualizing
  what is wished;
to take care of one's mind and body, exercising regularly, paying
   attention to one's own needs and feelings.

The interesting point in this, is that good coping skills are linked with resilience, and asking for help is considered a good coping skill. Which is akin to seeking sympathy, as charity between people is often motivated by sympathetic feeling, whether it was the intention of the sympathised to evoke it or not.
So in summary,
Is the 'addiction' to receiving sympathy similar to substance addiction or just a deficit of resilience?

I would conclude that there can be an addiction to drama, but not
sympathy.
A deficit in resilience could lead to sympathy seeking behaviours
due to needing extra support.
More likely, a deficit within the personality, that requires
attention and is part of a bigger disorder.


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How much additional sleep is required to recover from a given number of hours of sleep deprivation?
A previous question dealt with whether it is possible to catch up on lost sleep.
This question is a little different.
Assume that a healthy adult has been deprived of sleep for "x" hours.
How much sleep is required to restore healthy brain function, compared to sleep lost?
I wouldn't think the hours needed could be predicted by a linear scale.
Is there some predictable relationship between the two and what type of relationship is it?

Many times I feel it's not just about sleeping more hours and it will recover the hours u didn't slept before, I feel its more like, just go back to normal routine, and how many days you will need to get used to it again, imo, sleeping too much each time won't recover anything

I can give it some search, I dont know if it is exactly right that, or there is also some exact calcs. I tought that way because, evry1 has his body, every1 has different activitys with diferent effort and exhaustion levels, diferent evrything!, also, you can notice that when you sleep many hours at once you feel damn tired, still there might be some calcs and studs about that for sure, I'll give it a search when I have some free time since I'm intrested on it too :d

Closely related: http://cogsci.stackexchange.com/questions/1480/how-much-sleep-is-required-to-restore-maximum-cognitive-functioning

I don't see how this question is different from my previous one you link to? Did you read past the title? Closing it for now, I will reopen in case I misinterpreted.

It is funny that you ask this question. The answer is you can't. When you dont get enough sleep and you feel tired and your brain activity is lower (for example, trouble remembering what you were doing or where you left your keys) you cant catch up to it. You might take a powernap (not longer than 90 minutes) to give you a sensation of feeling awake, but the brain doesnt become more active. I dont know exactly why you cant catch up to lost hours of sleep, but you just cant. That also the reason, besides a messed up biogical clock according to light, why people working night shift experience more mental and health issues.


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Why are humans the only species to maintain relationships with other animals simply for pleasure?
In the wild, animals may share waterholes, and grazing areas. Some animals have symbiotic relationships one example being the hippopotamus and the oxpecker bird.
The symbiotic relationships are based on needs; Hunger, shelter, safety.
Human beings, appear to be the only species that has relationships with other species for pleasure. Companion animals and horses for riding are two examples.
Of course, there is also the use of animals to meet the species needs; eg dogs for safety.
In this question I would like to focus on the relationship between human beings and other species as a source of pleasure (or comfort).
What is different within the human brain that allows humans to maintain relationships with other animals purely for pleasure, that is absent in other species?

It is arguable that all relationships are symbiotic irrespective of species or gender. We are a social species so solitary confinement is a punishment. The company of anything with a brain is an improvement. Also genetic traits are transferable. Our nurturing instinct may have evolved to enhance the survivability of other family members (esp. children). Later that would transfer to domestic animals. Later still to a pet hampster.

Related: Do some people substitute pets for kids in their life?

According to Hal Herzog 2010's article "Are Humans the Only Animals That Keep Pets? Do monkeys keep pets?" in "Psychology Today", humans are the only animals that keep pets. Other animals have also kept pets however it was not under natural settings. These other "pet" relationships were observed in zoos, controlled experiments. etc.
One the main reasons Herzog notes that humans are the only animals to keep pets is the idea of culture. Humans have evolved to form a culture with social rules and norms. They can gather social information from others by relying on certain cultural rules. So it is acceptable for humans to form pet relationships with other animals. Some cultures do not have a word for pet. However ultimately these cultures end up forming relationships with animals that are "pet-like." The reason for this is because of memes. That is, the idea of having a pet spreads across different cultures.

SHORT ANSWER
It is likely that

any member of a social species (not just humans), being isolated from its peers (which individuals from other social species than humans also find stressful), will be searching for company, including from individuals from other species, "for pleasure" (various wrote about such mechanisms in humans during the covid-19 forced isolations and more generally, and there are some indication that this is true for other animals than humans); and that

having only examples of such relationships involving humans is a result of selection and reporting bias rather than of the lack of such relationships not involving humans (Herzog's argument boils down to "why don't chimps?", which states the lack of data to disprove his point rather than to data proving it, a clear case of reporting bias).

LONG ANSWER
Somehow, I feel that the question is based on shaky assumptions:

That the "pets" relation is hierarchical in nature (with one member of the relation, typically the human, dominating the other, for instance a dog or a cat or a fish).

That we know of all symbiotic relations in "natural contexts" (when we mostly know about those in human culture, and only poorly those which do not involve humans.

That "escaping solitude" is a "need" (and pleasure) typical of humans, when it is likely to be one for any individual of any social species (as much as hiding from the sky for preys of birds of preys), in the sense that it was positively selected by the evolutionary mechanisms.

Basically, I feel (no offense meant!) that the question is a case of asking "why is it that objects A with characteristics B,C,D,E,F,...,Y always have property Z?". Concretely, if you define

A = pets" such as having characteristics such as
B="Dominated species",
C=not (any more) for direct consumption (e.g. chicken),
D=not (any more) for help hunting (e.g. dogs),
E=not (any more) for help producing food (e.g. cows, goats,etc.),
F=not (any more) for help producing clothes (e.g. sheep, cows,etc.),
G=not (any more) for help keeping food safe from "vermin" (e.g. cats),
(...)
you will have made your definition so specific that, of course, only the cases you have in mind (human's "pets") match, and the coincidence should not be a surprise.

The very same Hal Herzog cited in another answer mentions the cases of

an  American Sign Language-trained gorilla adopting a cat,
a hippopotamus becoming friend with a tortoise,
an elephant and a dog, and
a group of a dozen or so bearded capuchin monkeys who were caring for a baby marmoset, another species of monkey.

Hal Herzog excludes the first 3 examples as "unnatural settings" (a flaky argument) and the last one as "the exception that proves the rules", an even flakier argument "whose meaning is contested" (especially with the modern meaning of the verb "to prove": it would be correct to say that "the exception *tests the general rules", but then the general rule must be discarded if it cannot be modified to encompass even the exception).
Alternately, if one was to define A (to avoid the word "pet") as "interspecies symbiotic relations between two members of distinct social species", Hal Herzog himself is giving instances of A which do not involve humans directly, both in the human culture (e.g. a dog and a cat sleeping together, a parrot and a turtle playing together) and outside of it (e.g. birds of other species peacefully sharing living quarters with a social colony of monk parakeets, parrots and monkeys being adopted into a colony of parrots and monkeys of a distinct species).
As such, I would make the research hypothesis that any member of a social species (not just humans), being isolated from its peers, will be searching for company, including from individuals from other species, "for pleasure". I would be curious to know the state of the art on such topic from an Ethological perspective!

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text:
Mental illness developing in midlife
There is much research about personality development and childhood. The onset of many mental disorders and illnesses, will occur in early adulthood. Studies are done to link certain childhood personality traits with the manifestation of the illness in adulthood.  Conversely, there is much research into the onset of aged onset dementia, Alzheimer's and the like.
With the exception of the Mid Life Crisis, I have not seen much research on the onset of mental disorders or mental illness in  adults during midlife, or approx. 35-50 years. What studies are there investigating major personality changes later in a person's life?
An example could be the percentage of new diagnoses of "a particular illness" for 35-50 year old age group.
I am not interested in an ongoing illness that was diagnosed as a younger adult and is  still occurring during this age group. I am interested in the  first time onset of an illness in an individual during these years.

I am not a professional, but it is my understanding that it is common for major depression to not show up in adults until the age of 30 to 60 years old; see for example, Table 2 of Lifetime Prevalence and Age-of-Onset Distributions of DSM-IV Disorders in the National Comorbidity Survey Replication, Mood Disorders - Major Depressive Disorder.  Overall, the most likely age group for any disorder to present itself is the years 30-44.
The beginning of the paper states: "Little is known about lifetime prevalence or age of onset of DSM-IV disorders".  The study included 9282 participants.

That seems like an excellent find, and quite surprising to me because what I've noticed is that the 20-somethings seem to deal with more powerful emotions and talk more about suicide than older people. I had thought it was due to higher hormone levels coupled with less life-experience. As people age, hormone levels drop and people seem to mellow-out. I'm not sure if that correlation is linked or just coincidental though. Just my 2 cents.  Anyway, I think this answer is useful and interesting.

@Randy My understanding is that one may have an inherited predisposition to a particular disorder (or disorders), such as major depression.  But the person may not show any symptoms of the disorder until there is some significant trigger, for example in the case of depression, the loss of a child.

@Skippy When I think of the phase "I hate my life and wish I was dead", its hard for me to imagine anyone over 30 saying it. The people who say this most seem to be the ones with the most going for them. They have their youth, health, and long future ahead. On the other hand, we have older people who crossed the peak who are dealing with a new grey hair each day, wrinkles, a spare tire forming, clogged arteries, family members are dying, maybe a dead-end job, etc, etc and yet, these are happier people. This is just what I've noticed and not nearly includes 9282 participants.

@tcrosley That could be. I don't know that much about it to say. In light of what I read in this article which may be of interest to you and Skippy http://www.thedailybeast.com/newsweek/2010/01/28/the-depressing-news-about-antidepressants.html I can't help but to wonder what the "malformation" in the brain would be that is inherited, since it doesn't appear to be serotonin related.

@Randy Various forms of mental illness are not inherited per se, but it is suspected that there is a genetic predisposition that is inherited instead -- that is, one is more likely than the general population to develop a specific mental illness.  In this study of twins for example, there was an 80% concordance for manic depression among identical twins (the highest of any trait listed).

@tcrosley Wouldn't twins also have similar environmental stimuli?  Could knowing you have a clone, itself, be reason for depression?  I think the fact that depression is highest on that list illustrates this possibility most. Why are you more likely to have depression in common with your twin than hypertension?  I'm not arguing against inherited, I'm just wondering by what means its inherited.  It could be inherited by environmental cues from the parents. Or it could be genetic.  I don't know.

@Randy Studies like this specifically use both identical (monozygotic) twins and fraternal (dizygotic) twins to control for this effect.  Note the differences in concordance in the table presented in the paper I linked to.

@Skippy no problem


text:
The relationship between narcissism and self-esteem
Given that personality disorders are rooted in abnormal experience and development. There has been much discussion about the aetiology of Narcissistic Personality Disorder. Having a concept of the causes of such an illness is helpful in establishing the answer to my question. The common belief was that beneath the arrogance of a narcissist, is an incredibly low self-esteem, hence the need to protect the fragile ego.

Those with narcissistic personality disorder believe that they're
  superior to others and have little regard for other people's feelings.
  But behind this mask of ultra-confidence lies a fragile self-esteem,
  vulnerable to the slightest criticism.

Mayo Clinic
I can see that there is some discussion refuting this, and postulating the opposite.

It was once thought that narcissists have high self-esteem on the
  surface, but deep down they are insecure. However, the latest evidence
  indicates that narcissists are actually secure or grandiose at both
  levels.

Psychology Today
I have wondered, how do we really know how the narcissist self-esteem is?
Is there an inverse relationship between narcissism and self-esteem or is the converse true?
Please provide a well researched answer.

I would like to see the evidence that indicates narcissists are secure. I have the 'feeling' if I saw such evidence, I could find flaws in the reasoning. Can you edit your question to include an example of a narcissistic person and show how it was determined they are secure?

@Randy In my conclusion some of them can be secure (its essentially a mixed bag), but narcissim ended up being a much more complex topic than "narcissists are secure or not secure."  Also, the big study I included was only patients that went to a doctor for apparently something.  In essence it wasn't testing the normal population.  There very well may be narcissists out there that get along fine - perhaps they realize they are a narcissist and consciously choose not to act like one.  I think that term is thrown around too loosely anyway...it's based on a greek story of a guy staring at himself

for very long periods of time to the point where he'd rather fall in love with himself than anyone else.  And in fact, as one of my citations points out doctors were still trying to figure out how to categorize it as a DSM in 2008.

First off, your second link there hasn't been reviewed since 2010.  I got a case study from 2013, an attempt to change the DSM for narcissism due to it's actual granularity and subtypes from 2008, and a letter to the journal of Indian Pscy med from 2012.

Seishin Shinkeigaku Zasshi. 2013;115(4):363-71.

[A case of major depressive disorder barely distinguishable from
  narcissistic personality disorder].
[Article in Japanese]
Saito S, Kobayashi T, Kato S.
Department of Psychiatry, Jichi Medical University.
The recent increase in cases of depression with a narcissistic
  tendency, especially among young individuals, has been pointed out.
  When the narcissistic tendency is conspicuous, patients may be treated
  for a personality disorder or pervasive developmental disorder, and
  not for a mood disorder. A case is described of a man in his late
  twenties who developed depression due to his failure in research work
  and job hunting, and, after a time, due to the break off of his
  engagement with his fiancée, manifested with narcissistic symptoms
  including an exaggerated opinion of himself, a sense of entitlement,
  interpersonal exploitation, lack of empathy, strong feelings of envy,
  and an extrapunitive tendency. He was regarded at the start of
  treatment as having narcissistic personality disorder. However,
  persevering treatment, mainly with supportive psychotherapy and
  pharmacotherapy including antidepressants (high dose of maprotiline
  combined with low dose of mirtazapine), sodium valprote and
  aripiprazole, finally improved not only his depressive symptoms, but
  also the symptoms regarded as a deriving from a personality disorder.
  He presented fierce  anger and aggression regarded as a mixed state,
  and showed the rapid improvement  in his depressive state after
  hospitalization, which we considered to show potential bipolarity. We
  diagnosed the patient with narcissistic depression, emphasizing the
  aspect which suggested a mood disorder, such as the episodic presence
  of narcissistic symptoms as long as a depressive state resided, his
  circular, recursive discourse, and his potential bipolarity. To
  accurately evaluate the aspect of mood disorders which patients
  appearing to show personality disorders have, it is considered useful
  to grasp a patient's condition from the viewpoint of a personality
  structure and viable dynamics. From a therapeutic standpoint, we
  suggest the importance of simple but persevering psychotherapy and a
  sufficient quantity of antidepressant medication for patients with
  depression, even if they are thought to have a personality disorder.
PMID: 23789317  [PubMed - indexed for MEDLINE]

Hmm well they seem to note initially that the converse is true in the first sentence.  We'll investigate why this is true soon too and the reasons for it.
Before even reading this, I hypothesized someone with bipolar disorder could have this type of problem...and sure enough...they mention the patient as potentially having it.

This one is back from 2008.  It seems like they were having some trouble with the DSM labeling of the disorder back then.  Apparently there are several different subtypes of narcissistic disorder, which could definatly seem viable.  So, so far your answer is 'sometimes'.

Am J Psychiatry. 2008 Nov;165(11):1473-81. doi: 10.1176/appi.ajp.2008.07030376. Epub 2008 Aug 15.

Refining the construct of narcissistic personality disorder:
  diagnostic criteria  and subtypes.
Russ E, Shedler J, Bradley R, Westen D.
Department of Psychology, Emory University, Atlanta, GA, USA.
  jonathan@shedler.com
Comment in
      Am J Psychiatry. 2008 Nov;165(11):1379-82.
OBJECTIVE: Narcissistic personality disorder has received relatively
  little empirical attention. This study was designed to provide an
  empirically valid and  clinically rich portrait of narcissistic
  personality disorder and to identify subtypes of the disorder. METHOD:
  A random national sample of psychiatrists and clinical psychologists
  (N=1,201) described a randomly selected current patient with
  personality pathology. Clinicians provided detailed psychological
  descriptions of the patients using the Shedler-Westen Assessment
  Procedure-II (SWAP-II), completed a  checklist of axis II diagnostic
  criteria, and provided construct ratings for each axis II personality
  disorder. Descriptions of narcissistic patients based on both raw and
  standardized SWAP-II item scores were aggregated to identify,
  respectively, the most characteristic and the most distinctive
  features of narcissistic personality disorder. RESULTS: A total of 255
  patients met DSM-IV criteria for narcissistic personality disorder
  based on the checklist and 122 based on the construct ratings; 101
  patients met criteria by both methods. Q-factor analysis identified
  three subtypes of narcissistic personality disorder, which the authors
  labeled grandiose/malignant, fragile, and
  high-functioning/exhibitionistic. *Core features of the disorder
  included interpersonal vulnerability and underlying emotional
  distress, along with anger, difficulty in regulating affect, and
  interpersonal competitiveness, features that are absent from the
  DSM-IV description of narcissistic personality disorder.* CONCLUSIONS:
  These findings suggest that DSM-IV criteria for narcissistic
  personality disorder are too narrow, underemphasizing aspects of
  personality and  inner experience that are empirically central to the
  disorder. The richer and more differentiated view of narcissistic
  personality disorder suggested by this study may have treatment
  implications and may help bridge the gap between empirically and
  clinically derived concepts of the disorder.
PMID: 18708489  [PubMed - indexed for MEDLINE]

And the story gets more complicated...to the point where there seem like many different types of treatment and just problems with therapists dealing with narcissists.
Q-Type Analysis:

grandiose/malignant
fragile
high-functioning/exhibitionistic

Core features of the disorder

included interpersonal vulnerability and underlying emotional
distress, along with anger
difficulty in regulating affect
interpersonal competitiveness

Looks like your question's answer is getting split up in many different ways.

I found this interesting letter that was sent to the Indian Journal of Psych Med.  It looks like there are specific type of strategies for dealing with specific types of issues....like for relationship issues there's one way, for other types...there's another.
I'll bold the interesting parts.

Indian J Psychol Med. 2012 Oct-Dec; 34(4): 403–404. doi:
  10.4103/0253-7176.108236  PMCID: PMC3662146 Demystifying Paradoxical Characteristics of Narcissistic Personality Disorder  Matthew
  Gildersleeve Queensland University of Technology, Brisbane,
  Queensland, Australia Address for correspondence: Dr. Matthew
  Gildersleeve, Queensland University of Technology, Brisbane,
  Queensland, Australia.

  Sir,
This letter is aimed for psychotherapy clinicians and researchers who
  should acknowledge the relationship linking Kohut's self-psychology
  and Glasser's Choice theory that can demystify relationship
  difficulties and mental health problems in narcissistic personality
  disorder (NPD). NPD is commonly experienced interpersonally by others
  as insufferable, pompous, and un-empathic.[1] NPD persons have been
  identified to possess giant self-centeredness, a certainty that they
  own supreme personality, and their humiliation of others makes them
  intolerable for interpersonal relations.[1] Importantly, Heinz Kohut's
  legacy to psychology is known as self-psychology and was centered
  principally on narcissistic personality development and treatment.[2]
  Suboptimal psychological development is thought to arise when maternal
  compassion is discriminately substandard.[3] As a result, the
  narcissistic self constructs a defense against the helplessness of a
  hurtful world.[3] Kohut[2] cited in Banai et al.[3] called the
  compassion required from maternal figures as “self-object needs”
  because these needs develop the self-image and are provided by
  external objects.     (Oh wow, it seems like they're talking about entitled rich kid's attitudes, that's kinda funny, interesting).
By not receiving necessary self-object transferences through decisive
  epochs in development, the young individual cannot build the
  competence to control self-respect or construct a positive
  self-image.[3] *Consequently, the child, now an adult, depends on other
  humans to construct their self-image. The self-object transferences
  received as an adult provide a feeling of significance, which was not
  established during child development.[3] However, NPD persons are
  apprehensive of meeting self-object absence as an adult.[4] In order
  to feel the control of their fate, NPD persons present a mindset of
  dominance in the interpersonal sphere. As a result of this
  authoritarian manner, persons with NPD typically have a record of
  numerous unsuccessful relationships.[4]*
Go to: PARADOXICAL CHARACTERISTICS IN NARCISSISTIC PERSONALITY
  DISORDER Thus far, this letter has acknowledged that NPD persons rely
  heavily on self-object transferences to develop a positive self-image.
  The behavioral characteristics of NPD persons reflect this need and
  are well documented.[5] However, what is paradoxical about these
  behavioral characteristics is that instead of behaving in a way to
  increase the chance of receiving self-object transferences in
  relationships, NPD individuals act in a way to reduce that possibility
  by destroying interpersonal relations.
(So not only have we seen narcissists become depressed...they also have the propentencity to do things in relationships that sabotage them....which may then lead to this depression.)
Glasser[6] has specified relationship building and destroying behavior
  in a grand detail in his Choice theory. “Seven Caring Habits” and
  “Seven Deadly Habits” offer superb rules for how psychotherapists
  should interact with clients to enhance the likelihood that these
  individuals use caring interpersonal habits to attain optimal mental
  health. It is evident from the literature that NPD behavioral
  characteristics reflect the “Seven Deadly Habits.”[1] Glasser's Seven
  Caring Habits are Supporting, Encouraging, Listening, Accepting,
  Trusting, Respecting, Negotiating differences and the Deadly Habits
  are Criticizing, Blaming, Complaining, Nagging, Threatening,
  Punishing, Bribing, or Rewarding to Control.
Go to: CHOICE THEORY The writing of Kohut and advocates of
  self-psychology argue that the feeling of love, belonging, closeness,
  and connectedness with other humans are essential for individuals with
  NPD who requires self-object transferences.[7] Unfortunately, the
  pushing, demanding actions (Seven Deadly Habits or External Control
  Psychology) being used by NPD persons destroy relationships and
  therefore prevents self-object needs being met. When external control
  is used by NPD persons, it will destruct the capacity of one or both
  individuals to locate contentment, eventually resulting in severed
  relationships.[8] This interpersonal disengagement is argued to be the
  foundation for the majority of human mental illness.[6] Choice Theory
  and the Seven Caring Habits are offered to replace external control
  psychology and the Seven Deadly Habits[6] to preserve relationships
  and optimal mental health.
External Control Psychology is an attempt to control others to act in
  a way they do not want to.[6] This ideology of a person who uses
  external control does not permit individuals outside the self to
  formulate preference about individual freedom, and advocates that
  other individuals should be punished to modify their behavior to
  attain the controllers' needs.[6] The “Deadly Habits” demolishes
  individual freedom of the oppressed individual and therefore acts to
  disconnect relationships, as freedom has been identified as one of the
  basic human needs.[6]
Consequently, a central thesis of Choice theory is that the only
  individual one can be in command of is themselves.[6] If the
  individual believes they can command other humans, then they will
  encounter anger and irritation leading to mental illness.[6] Anger,
  irritation, and mental illness will also arise if the individual
  believes that other humans can command them and then externalizes
  blame to the perceived controller for undesirable events.[6] For that
  reason, it is vital for the NPD individual to focus on internal
  control of their own choices and to value the rights of other people
  who have their own needs.[6]
In conclusion, it is important that the caring habits be taught to the
  NPD client, once a therapist has identified an individual with strong
  self-object needs and who meets the criteria for NPD. Using Choice
  theory, the psychotherapist directs an individual toward fulfilling
  interpersonal relationships and educates the person to relate in more
  helpful modes using internal control psychology.[6] The better NPD
  persons are proficient at bonding and comprehending other individual
  needs, the better prospect they possess to receive positive
  self-object transferences and happiness.

  Go to: ACKNOWLEDGMENTS Thank you to Amy-lee Weisse for constructive
  discussion and invaluable guidance.

  Go to: REFERENCES
  1. Millon T, Millon CM, Meagher S. Hoboken, New Jersey: John Wiley & Sons; 2012. The Narcissistic Personality. Personality Disorders in
  Modern Life; p. 330.
  2. Kohut H. Chicago: University of Chicago Press; 2011. Introductory Considerations. The Analysis of the Self: A Systematic Approach to the
  Psychoanalytic Treatment of Narcissistic Personality Disorders; p. 1.
  3. Banai E, Mikulincer M, Shaver PR. “Selfobject” needs in kohut's self psychology: Links with attachment, self-cohesion, affect
  regulation, and adjustment. Psychoanal Psychol. 2005;22:224–60.
  4. McLean J. Psychotherapy with a Narcissistic Patient Using Kohut's Self Psychology Model. Psychiatry. 2007;4:40–47. [PMC free article]
  [PubMed]
  5. Silverstein ML. Washington, DC: American Psychological Association; 2007. Narcissitic Personality Disorder, Disorders of the Self: A Personality-Guided Approach; p. 27.
  6. Glasser Bloomington: IUniverse; 2011. Replacing External Control With The New Choice Theory Psychology. Take Charge of Your Life: How
  to Get What You Need with Choice-Theory Psychology; p. 8.
  7. Strack Hoboken, New Jersey: John Wiley & Sons; 2005. Self Psychological Foundations of Personality Disorders. Handbook of
  Personology and Psychopathology; p. 181.
  8. Glasser , Glasser New York: Harper Collins; 2007. External Control Can Kill a Marriage. Eight Lessons for a Happier Marriage; p. 11.
  Linkback here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3662146/

So, it looks like there's alot of stuff going on with Narcissists.  Or what they call "NPD."
As for my conclusions:
NPD or (Perceived NPD) or actually scientists are still trying to figure it out I'm going to put into three categories that even have subcategories.
1)  Being the center of attention and always getting what you wanted
while growing up...only to realize when it times come to get a job
that doesn't exist anymore - which can admittedly be a difficult
shift for someone to have to make.  This could also stem from
derivatives of this.  Obviously would say psychopathology here and environmental    influencers are important players.**
The affects of this seem to appear as relationship issues mostly - as
they have developed a certain "expectation for this or that" which
puts stress on their mate....whom then eventually leaves
them....which then causes them to be a depressed narcissist.  This
cycle also seems to repeat itself although methods are suggested to
help treat a patient with this disorder in the last piece of
literature.
2)  Genuinely having some subtype of NPD that is more than just psychopathologically based.
This goes back to that 2nd study where they were trying to identify the subtypes for the DSM definition.  These adjectives don't seem to describe someone who would necessarily fit into category #1, although they partially seem to discribe someone who would fit into my 3rd category - someone who is simply bipolar and has a "narcissistic mania."  And yes, I just made that medical diagnosis up.
Q-Type Analysis (the authors labeled these as the three subtypes):

grandiose/malignant
fragile
high-functioning/exhibitionistic

Core features of the disorder (NPD)

included interpersonal vulnerability and underlying emotional
distress, along with anger
difficulty in regulating affect
interpersonal competitiveness

So I actually don't really believe many #1's would fit into this #2 category I have set up due to the lack of focus on problems in certain types of relationships (they mention interpersonal failures...but not as directly).
I'd say these are most likely people with a true "NPD" pathology - with  a couple bipolar's mixed in depending upon if their methodologies were very affective at weeding them out and since it's a Q-type analysis...I'd feel somewhat unconfident about that.
3)  Someone who is bipolar and when they have their manic episode, they become narcissistic.  Obviously they'd go up and down and have all sorts of fun problems.
Answer to your question:
They can be both, either/or, have it depend upon things like interpersonal issues because they feel like the world owes them something. Apparently the pathology of narcissism is a very complex thing to figure out or put any sort of hard and fast label on.  It could be caused by one's psychology from how they were raised or a genuine mental disorder of a physiological kind. There's also problems with distinguishing it from bipolar disorder (although I'd say if someone had bipolar disorder then they'd probably know it).

Lol, everyone likes your question but not my response.  It seems like people just want short answers even to questions that are hard to fully respond to. Sigh.

@user3433 I love your answer. Having been married to what I have finally figured out is a narcissist for 20 years, there was a lot of clicking going on in my brain when I read it.


text:
The effects of pain on cognitive function and incidence of depression
There have been studies about  the link between depression and cognitive function..
There have been studies between pain and cognitive function. This has, also, been discussed in this question here.
There have been studies linking pain and depression.
From a biochemical viewpoint:
Are pain, depression and cognitive function intrinsically linked?
Is it possible for chronic pain not to have an effect on cognitive function and the likelihood of depression?

Can't find the citation now, but I remember reading in the Nytimes that allergies lead to greater depression. This is almost tangential to your question except for the fact that the reasoning mentioned in the article is that allergies lead to and immune response, then leading to flu like symptoms (including "pain") which leads to depression.

This may be more of a non-answer than an answer, but here it goes.
When you're talking about the effect of something like pain, it's valuable to first understand some of the complexity. While it's easy to put things in boxes in practice, (physical pain, emotional pain, etc.) it's very difficult to put those things in boxes when you're talking about a neuropsychological response like pain. While there are breakthroughs being made in understanding specific parts and functions of the chemical soup that is the human brain, it's still largely a mystery as to how those parts interact, not to mention how our psychological state affects/is affected by our brains.
Can pain affect mood and general ability to function? I think it's safe to say it can. When we feel pain all kind of stress hormones with significant amounts of adrenaline, (such as Corticosteroid) are release that ideally will only be there for a short amount of time and then fade away. When you have chronic pain, your body doesn't get a chance to recover from the heightened state of arousal. This is known to affect many parts of general function negatively and probably is somewhat similar to the affect of long term chronic pain.
As far whether there is an intrinsic biochemical link between an actual depressive disorder and the brain's ability to function, I think there just isn't enough understanding about what happens in the brain to answer that properly. Depression itself is still a hot topic of debate as to how it develops, and since plenty of evidence supports it being both a psychological and neurological disorder, it would also depend on the individual's psyche as to whether they would develop depression. Pain, even chronic pain, has been dealt with successfully by people without much change in their life. Chronic pain has also destroyed people's lives. Any response is probably possible. At this point there are simply too many variables (many of of which are not yet understood) in order to make any statement as to what is normal.
The brain has really only began to be explored and understood, and while theories abound, with many questions like this the only honest answer at this point is that we don't know. At least not yet.

tysm for answering, I thin this is an intelligent argument. I was hoping we may have more references, but nevertheless, I am really pleased you gave an answer. thanks Peejweej


text:
What are the psychological mechanisms for compulsive talkers?
What are the psychological mechanisms for people who can't seem to help frequently "talking too much"?
Specifically, I am referring to those that recognise cues to when someone is busy, disinterested or distracted, but are compelled to continue talking.

Compulsive talking appears to be linked with the inability to manage social anxiety. Whether the anxiety is brought about from the uncomfortability of the interaction or from the avoidance of deep seated feelings within the individual.

People who score beyond two standard deviations above the mean on the
  scale are labeled as “talkaholics,”

as cited by James C. McCroskey & Virginia P. Richmond

The most common and basic cause of any compulsive behavior is anxiety.
  A person engages in compulsive behavior not because he particularly
  wants to, but because he’s so anxious that he has to do something to
  get his mind off that anxiety. Until the compulsive talker comes to
  grips with whatever he or she doesn’t want to think about, the talking
  will continue.
The root of this anxiety varies from individual to individual. But it
  often stems from deep-seated emotions of insecurity and
  inadequacy.../...
For the compulsive talker, silence and reflection are simply
  unacceptable. A pause in conversation is an emotional abyss into which
  they simply cannot help but throw themselves.

written by Dr Hurd
Compulsive talking could be confused with Pressure of Speech. Which can be associated with mania and attention deficit disorder. Pressured speech is marked by speaking rapidly, with a sense of urgency and, frequently, with no social awareness.
Logorrhea is another condition, which causes the person to talk endlessly, but, usually, in an incoherent, rambling fashion.

Identifying compulsive communicators: The talkaholic scale
James C. McCroskey & Virginia P. Richmond
Communication Research Reports
Volume 10, Issue 2, 1993
Talking too much can have deep-seated roots
Dr Hurd
Private Practice of Psychotherapy and Solution-Focused Consultation since 1988.
Multiple published works.


text:
What is the neurological mechanism behind the feelings associated with loneliness?
Loneliness can be debilitating, and the feelings associated with it can be overwhelming, including feeling 'cold inside', sad, hopeless and even helpless.
Many things can 'cause' loneliness', both real and perceived, but what I am interested in is not the causes, but the neurological mechanisms that cause the feelings associated with loneliness.


text:
What is the psychology behind choosing to be weird?
There is a saying I was once told:

"I no longer fear going insane, I am enjoying every moment of it"

For some (including myself), this is in fact a rather happy and liberating reality, albeit a reality that I don't quite understand.  So, my question is, what is the psychology behind choosing to let one's weird side show?
Please note - I am not asking for self help, don't need it - just trying to understand the psychological aspects.  An example of this is when I wore a ballerina suit and walked around a shopping centre as if nothing was out of the ordinary... it was not a pretty sight

The psychology behind choosing to let one's weird side show?
I think the this question would work as effectively as:
The psychology behind choosing to let one's individuality show?
Human beings are social animals. Social pressures  play significant factors in moulding personality.

The term conformity is often used to indicate an agreement to the
  majority position, brought about either by a desire to ‘fit in’ or be
  liked (normative) or because of a desire to be correct
  (informational), or simply to conform to a social role
  (identification).

So assuming "weird" is more likely to be further away from social norms. The more social pressure to be borne. This means a greater courage is needed to be oneself. There are links between self-acceptance, social pressure and depression.

Correlational results indicated that all three trait dimensions of
  perfectionism (i.e., self-oriented, other-oriented, and socially
  prescribed perfectionism) were associated negatively with
  unconditional self-acceptance. Also, as expected, depression was
  associated with relatively low unconditional self-acceptance. Finally,
  a path analysis revealed that unconditional self-acceptance mediated
  the association between socially prescribed perfectionism and
  depression, and other-oriented perfectionism was found to affect
  depression only indirectly through its association with low levels of
  self-acceptance.

Dimensions of Perfectionism, Unconditional Self-Acceptance, and Depression
Gordon L. Flett, Avi Besser, Richard A. Davis, Paul L. Hewitt
Journal of Rational-Emotive and Cognitive-Behavior Therapy
June 2003, Volume 21, Issue 2, pp 119-138
Conclusion
Gaining self-acceptance, one's individuality or "weirdness" is inversely proportional to the incidence of depression; and also improves the individual's capacity to cope with social pressure to conform.  So by accepting one's strengths and weaknesses one is freed from (social and psychological) pressure, improving one's sense of well being.

By being weird you choose a smaller group of similar weirdos to compete for status in. At the limit you're in a group of one. Smaller peer group, easier to be near the top. High status feels good even if it's in a smaller peer group.
It's relatively easy to be the manliest brony as opposed to being the manliest human.
Disclaimer: I'm not an expert.

Have you got references to include with your answer?  Your 2nd sentence does not really make sense to me.

@Skippy Oh I see where this is going... If you're weird, you're an outcast, but by embracing your weirdness and joining with other outcasts, now you're an accepted member of a group. This could be why people choose to be weird rather than working to be normal.

@Skippy You mean someone running from the law and constantly looking over their shoulder? I mean someone weird as in dressing in a ballerina outfit and walking around the mall. What would be the motivation? It may be easier to make friends in a ballerina suit than a business suit where you have to compete with 10000 other joes in a business suit. I think that was the idea behind this answer. True or not, idk, but I think that's Ansis' thought process.

Can you find some references for this answer Ansis? As it stands now it's attracting downvotes and flags and will likely be converted into a comment.


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What motivates individuals to engage in cyberbullying?
With the advent and proliferation of social media, forums and q&a sites, there has been a matching increase in the incidents of online-bullying, or 'cyber-bullying, that goes beyond trolling. All too many times, the consequences of this kind of bullying (like any type of bullying) can be tragic.
What is the psychological motivation behind the cyber-bully?  Is it a consequence of them feeling empowered by their apparent anonymity?
I have read the post "Why do teenagers take the internet and cyberbullying so seriously?", but my question is focused on the psychological motivations that the perpetrator of cyberbulling has, not why it is so damaging to the victims.
I am after authoritive (refereed) articles about this.

From my understanding of the problem and my years of experience with the internet since the early days when IRC was popular and web forums were just starting to emerge, I believe I can shed some light on this subject. probably not enough for a full answer but more than just a comment.
I feel that a large part of the problem is the anonymity (or perceived anonymity) as well as the sense of detachment that communication over the internet provides us with. I think that psychologically it is much easier to be critical, mean, cruel and otherwise have a lack of empathy when not dealing with another person face-to-face or verbally. Just as text-based communication does not convey tone of voice to allow us to know when others online are being sarcastic, one can lose the sense of how much one's actions are hurting others when they are cruel online.
With respect to perceived anonymity, it becomes greatly easier to rationalize or entirely forget that one's actions have consequences. It's easy to attack someone online and never have them know who is attacking them. This is demonstrated by a 2005 study done by Qing Li of the University of Calgary (I am unable to find the actual link to the study but have found many places which reference it) that states that 41% of students surveyed did not know the identity of the perpetrators. To me this indices that the anonymity provides a means for humans to rationalize behaviors we otherwise would be ashamed to be associated with.
The paper Cyber bullying:  Clarifying Legal Boundaries for School Supervision in Cyberspace by Shaheen Shariff/McGill University, Canada and Dianne L. Hoff/University of Maine, Orono, USA also draws some very interesting parallels between cyberbullying and the 1954 novel Lord of the Flies by  William Golding, speaking to the roots of cruelty in human nature as well as lack of supervision/perceived anonymity:

Young people in cyber-space lose their inhibitions in the absence of no central power, clear institutional or familial boundaries, or hierarchical structures (Milson & Chu, 2002). As Bandura (1991) explained over a decade ago, physical distance provides a context in which students can ignore or trivialize their misbehavior, as easily as Golding’s boys did on their distant island. In cyber-space this form of disengagement is amplified
Lack of institutional and parental rules in cyber-space have the effect of creating virtual islands similar to the physical islands in Lord of the Flies. The absence of adult supervision allows perpetrators free reign to pick on students who may not fit their definition of “cool” because of their weight, appearance, accent, abilities or disabilities (Shariff and Strong-Wilson, 2005). Cyber-space provides a borderless playground that empowers some students to harass, isolate, insult, exclude and threaten classmates. [...] Without limits and clear codes of conduct, communication in cyber-space (even among adults) can rapidly deteriorate into abuse because of the knowledge and sense of security that comes with the limited possibility of being detected and disciplined.

It also talks about teenage hormones being a driving factor:

Moreover, adolescent hormones rage and influence social relationships as children negotiate social and romantic relationships and become more physically self-conscious, independent, and insecure (Boyd, 2000). Research on dating and harassment practices at the middle school level (Tolman, 2001) shows that peer pressure causes males to engage in increased homophobic bullying of male peers and increased sexual harassment of female peers to establish their manhood. During this confusing stage of adolescent life, the conditions are ripe for bullying to take place. The Internet provides a perfect medium for adolescent anxieties to play themselves out.

I associate it somewhat with the notion by Thomas Hobbes that humans are "warlike", that by our very nature we are completely self-centered, and that we form societies and governments by giving up some of our selfishness and collectively adhering to social contracts for a greater good. By the nature of online communities often we lose this sense of responsibility to the community and each other, and we are prone to regress to our more basic, warlike state. This is my personal belief; I am still searching for actual references with which I can back this up with.

I am aware that this answer lacks the authoritive (refereed) articles you're requesting, Damien. I do not intend this to be the accepted answer unless I can find such articles but rather my own thoughts on this with references I could find, in hopes of spurring more answers. In fact I am tempted to offer a bounty for authoritative answers when the option becomes available.

This is still a very good answer - it has both authoritive resources and knowledge from your experience (which to me, makes it far better).


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What causes some women to have repeated abortions?
Fisher et al. (2005) studied the characteristics of women who have repeated abortions. The study was conducted in countries where reliable contraception and education about birth control are readily available. There appears to be a link between a history of physical or sexual abuse and women who have repeated abortions.
However, not all women having repeated abortions have been abused. Another factor must come into play for non-abused women having repeated abortions.
Thus, my question is:
What other factors besides physical and sexual abuse cause some women to have repeated abortions?
Some examples might include poor living skills, lack of education, low self esteem, self abuse, socioeconomic conditions, a true desire to have a baby, ambiguity about wanting a child, fear of being a bad parent, fear of being tied to an abusive partner, lack of responsibility etc. This list is by no means exhaustive.
References

William A. Fisher, Sukhbir S. Singh, Paul A. Shuper, Mark Carey, Felicia Otchet, Deborah MacLean-Brine, Diane Dal Bello, and Jennifer Gunter   Characteristics of women undergoing repeat induced abortion  CMAJ. 2005 March 1; 172(5): 637–641.

Thanks JeromyAnglim! It looks much better to me. What do you think now @what?

@JoshGitlin Same here. What do you think of my additional edits?

@JeromyAnglim I took your edits a bit further. Please roll back, if you disagree.

Looks fine to me @what! Skippy, do you feel the original intent of your question has remained intact?

It is certain that a desire to have sex without contraception and a lack of desire to be a parent cause women to have multiple abortions. (precluding rape)

A certain amount of a desire to have sex is natural. Causes for increased sexuality are so numerous that is not tenable to search.
Risk taking behaviour is associated with sex without contraceptions. A stable long term relationship might be one reason to have sex without protection where the risk is perceived to be less based on the lack of infidelity. A lack of responsibility could also motivate someone to consistently not use protection. Peer pressure by the male or even religion is also possible.
Finally there are many reasons people decide not to be a parent. Primarily they are unable to be a mentor and they are incapable of nurturing. There are many additional reasons at this link about why certain reasons to have children are irrational. However it should be stated that just because one is incapable of being a good parent doesn't leave abortion as the only option. The child can be given up for adoption however that is not popular.


text:
What personality traits affect ability to cope with pain?
It has been shown that pain impairs cognitive function,  in this question and the following studies on the effects of  headaches on cognition. Moor et al write

It must therefore be emphasised that headache pain appears to impair
  general task performance, irrespective of task complexity, rather than
  specific attentional mechanisms. Headache pain has an effect on the
  core cognitive components necessary for the successful completion of
  tasks, and in particular those involving the updating of the cognitive
  system.

Eccleston et al have shown that the  degree to which pain disrupts  cognitive processes  is  related to facts regarding the pain and the individuals psycho-social activities.

The interruptive function of pain depends on the relationship between
  pain-related characteristics (e.g., the threat value of pain) and the
  characteristics of the environmental demands (e.g., emotional
  arousal).

So, it seems that there is physiological and psychological factors that contribute to why pain interferes with cognition.
Are there personality traits that correlate with an individual's ability to cope with pain?
References

Headache impairs attentional performance.  Moore DJ, Keogh E, Eccleston C.  Centre for Pain Research, The University of Bath, Bath BA2 7AY, UK.
Pain demands attention: A cognitive–affective model of the interruptive function of pain.  Eccleston, Chris; Crombez, Geert   Psychological Bulletin, Vol 125(3), May 1999, 356-366. doi: 10.1037/0033-2909.125.3.356

Similar, but not a dupe http://cogsci.stackexchange.com/questions/3929/what-are-the-neurological-differences-between-those-who-have-a-high-tolerance-to

nor do I, which is the reason I wrote Similar, but not a dupe and upvoted the question.

Gathered from M. Pecina et al., “Personality Trait Predictors of Placebo Analgesia and Neurobiological Correlates,” Neuropsychopharmacology, doi: 10.1038/NPP.2012.227, 2012:

A recent study has found that personality traits appear to influence
  how strongly a person responds to a placebo treatment for pain.

http://www.psychologytoday.com/blog/unique-everybody-else/201301/personality-and-pain-relief

Pain relief tended to be stronger in participants who rated themselves
  higher in the personality traits of ego resiliency and agreeableness
  and lower in neuroticism.
  [...]
  The facets that predicted placebo response most strongly were high altruism and straightforwardness (facets of agreeableness) and low angry hostility (a neuroticism facet that is also related to low agreeableness).

More thorough explanations are found in the link provided.
Further information on the same study:
http://www.the-scientist.com/?articles.view/articleNo/33300/title/Personality-Predicts-Placebo-Effect/


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Which morals are universal across the species?
This is the first of a series of three questions about morality:
There are sets of moral standards within any given society. What one society deems as acceptable may be deemed as abhorrent in another. This concept lends itself to the idea that some aspects of morality are learnt and not innate within an individual.
Which morals are universal across the species?
The second question: What is the psychology of morality?
The third question: How is individual morality linked to psychological profiling?

This is a partial answer to your question.
According to "Only Humans Have Morality, Not Animals", (Guldberg, 2011), claims that morality is something unique to humans.  Basically the author concludes with:

Human beings are not perfect and never will be, but we are special and unique among the animal kingdom. We are capable of making judgements about our own and other people's behaviour, and have the capacity consciously to change the way we behave and society as whole.

A key argument made in the article is that there is a great difference between instinctual connections and actions and human empathy and morality.
Further, according to the article "Is Morality Innate?" (Prinz), proposes that:

Morality is a byproduct—accidental or invented—of faculties that evolved for other
  purposes.

and proposes a somewhat negative, yet true conclusion:

Nonhuman animals are often
  violent, but their potential for bad behavior may be lower than ours. Because we can
  reason, there is a great risk that human beings will recognize countless opportunities to
  take advantage of our fellows.

Essentially, it seems that perhaps morality is unique to humans owing to our abilities to reflect, reason as well as react.

There is a famous Ted talk on the topic of fairness, by Frans de Waal. It does not really address the question of whether the moral of fairness is universal across all species, but makes a very interesting case that fairness might be "universal" across primates at least:
http://www.ted.com/talks/frans_de_waal_do_animals_have_morals.html

I can think of a view.

Love toward ones' offspring. That's pretty universal.
Not harming others, especially those that can hit back. Lions don't attack stronger lions. Weaker chimps obey stronger chimps. Peasants obey their tyrants while both self deceive themselves that it's for some higher purposes. Basically both sides realize that mutually assured destruction sucks that both choose the higher road.


text:
What are the neurological mechanisms behind risking one's own life for another?
Every so often, we hear of people who go that extra mile and put their life on the line (and sometimes, give their life) for another person - whether it is a loved one or a complete stranger (sometimes, an enemy).
This has happened to me and several people that I know - and there many cases floating around in the media, a couple of examples are Jordan Rice and Joan North, there are millions of cases such as this, where ordinary people, young and old have 'stepped up' and did all they could to help.  Nearly all of them reject the title 'hero'.
Having experienced this myself, I can honestly say, it was not really a 'choice', but a 'compulsion' - seemingly, the reflexes seem to become more acute, the reactions faster and fear is either suppressed or gone altogether.
So, my question is, what are the neurological mechanisms that compel a person to act to help another, often without regard to their own safety?

This book What Makes a Hero?: The Surprising Science of Selflessness by Elizabeth Svoboda, covers the answer to this question in considerable detail.
The author explores the genetic predisposition to be heroic, whether it can be developed and learnt, and the idea of group selection; which proposes this is an instinctual reaction, the sacrifice of one member can be in the aide of the greater good of the species.
This discussion on Moral maze  examines whether human altruism really exists, or whether it is an evolutionary process. Examples of mutual reciprocity within various species, demonstrates that self-sacrifice can contribute to an individual's overall well-being. It is a cynical look at human nature, making the basic assumption that the survival instinct within human beings (or the preservation of an individual's gene pool)  is the greatest drive and that any seeming detour from this, ultimately serves this.

"Even in human societies we can still trace many behaviours seemingly
carried out for the benefit of the group back to benefits for the
individual," Stanford explains.
"Someone who jumps into a river to save a drowning man will become a
hero. And heroes accrue all sorts of benefits. For example, they may
become more attractive to women," he adds.

My personal take on the two examples you provided:
In the case of Jordan Rice he has sacrificed himself for his younger brother. An act that conforms with the notion of group selection and maintains the integrity of the individual's aim to preserve the own gene pool.
In the case of Amanda (aka Joan) North is quoted as saying:

I felt like there was a reason I was there. I felt a  compulsion to go over to you.

Amanda North is in her 50s and has two children; past her child bearing and raising years (from a survival viewpoint).
Erika Brannock (the woman Amanda North rescued) is a 29 year old woman. A member of the species in the prime of her child bearing years, hence better able to contribute to the ongoing survival of our species. An added, an unrelated observation, is that she also happens to be a preschool teacher - demonstrating the, more likely odds, that she is a member of the species in the role of raising the next generation.
A note  about the state of mind of a person in such a crisis, it is survival mode at it's most primitive. The body's fight and flight response, with is managed by the sympathetic nervous system. This optimizes the individual's for self preservation and protection of others.
The body's reaction to fight and flight:

heart rate and blood pressure increase

pupils dilate to take in as much light as possible

blood-glucose level increases

muscles tense up, energized by adrenaline and glucose (responsible    for goose bumps -- when tiny muscles attached to each hair on surface
of skin tense up, the hairs are forced upright, pulling skin with
them)

smooth muscle relaxes in order to allow more oxygen into the lungs      nonessential systems (like digestion and immune system) shut down to
allow more energy for emergency functions

trouble focusing on small tasks (brain is directed to focus only on    big picture in order to determine where threat is coming from)

Why Do People Risk Their Lives To Help Others During Emergencies Such as the Boston Marathon Bombing?
note - if you like I can investigate studies which show the demographics of likely heros, which is a little out of the scope of this question.


text:
Is the condition Pathological Intoxication recognised as real?
The plot of the movie Final Analysis revolves around a murder committed by a person diagnosed with Pathological Intoxication.
The following study confirms the:

probable existence of a discrete syndrome of pathological reaction to
  alcohol without reference to the amount of alcohol consumed.

The Diagnosis of Pathological Intoxication
Barry M. Maletzky
Volume 37, 1976 > Issue 09: September 1976
Journal of Studies on Alcohol and Drugs.
However there are doubts as raised by the following article.

The existence of pathological intoxication as an entity must remain in
  doubt unless the disorder can be reproduced under controlled
  conditions.

Pathological intoxication--is there such an entity?
Hollender MH.
J Clin Psychiatry. 1979 Oct;40(10):424-6.
I can see other conflicting articles; What is the latest position on Pathological Intoxication?

Pathological Intoxication was removed as a diagnosis from the DSM-IV (the psychiatric diagnostic manual used by American psychiatrists) when it was published in 1994, but was left in the ICD-10 (the diagnostic manual published by the World Health Organization) which was published in 1992. The decision to remove the disorder from the DSM-IV was based on literature reviews indicating there was no evidence for a separate syndrome of pathological intoxication (Salloum & Mezzich, Psychiatric Diagnosis: Challenges and Prospects, 2009, John Wiley & Sons, pg. 123). The disorder is not included in the DSM-5, which was published in 2013. The ICD-11 draft redirects searches of "pathological intoxication" to the "alcohol intoxication" entry; pathological intoxication is listed as a narrower term, but no additional information is provided (http://apps.who.int/classifications/icd11/browse/f/en#/http%3a%2f%2fid.who.int%2ficd%2fentity%2f1339202943).
A 2012 review (Fuelner, T., The minotaur defense: The myth of the pathological intoxication defense, American Criminal Law Review, 49(i4), pp.1969-1999; https://www.ncjrs.gov/App/Publications/abstract.aspx?ID=264897) provides an overview of the historical and current medical and legal definitions of the condition. The author concludes that the concept has largely been discredited in psychiatry, but has some continued support in legal circles. However, the author argues the use of the condition in criminal defense should be eliminated.


text:
How sexual activity influences a woman's sex drive
Sheila Gregoire suggests that increasing the amount of sexual activity increases a woman's sexual desire in general.
I can postulate that child bearing and raising impacts significantly upon a woman's life and that possibly, when a woman finds a mate worthwhile, it is a primitive drive to reproduce.
In  studies by Winnifred B. Cutler, it is demonstrated how, as sexual frequency declines so does sex drive, for women.

HOW SEXUAL FREQUENCY AFFECTS
A WOMAN'S SEXUAL RESPONSIVENESS,
FERTILITY, AND HEALTH
Paul H. Byerly

Is it true that having sex increases a women's future desire to have sex?
What physiological purpose does this serve?

Nice question. I'm a man and I'm not sure Cutler has it right for men. Anecdote: When I had sex, I am very horny the next day. If I don't have sex for some time, I forget about it. Anecdote: Canadian comic artist Dave Sim decided to become celibate. He says: "If you don't scratch it, it doesn't itch." Nuns and monks say something similar. Probably the reason for abstaining from sex has something to do with the increase or lack of increase in desire: if you want sex but can't have it, you'll want it more desperately with time. If you are otherwise occupied, you won't miss it.

The inverse of your first question might hold generally true: that desired sexual frequency could influence a woman's actual sexual frequency.
Willoughby and Vitas (2012) conducted a study focusing on the sexual desired discrepancy between male and females. They make reference to sexual desire discrepancy (SDD) - difference between one's desired frequency of sexual intercourse and actual frequency of sexual intercourse.

High SDD may then lead some females to put more resources into the
  relationship in order to work toward future sexual contact and
  increase the intimacy and closeness in their relationship. In this
  way, SDD may serve among female partners as a motivator to enhance and
  support the relationship as it progresses toward higher sexual
  frequency.

It mainly would depend on the quality and satisfaction of the sexual intercourse that would determine whether a woman's desire for greater sexual frequency would increase or not. Assuming that quality and satisfaction of sexual intercourse is high for the woman, I would say that this would increase a woman's future desire to have sex. Processes on positive expectancies give rise to higher perceived quality of the sexual relationship (McNulty & Fisher, 2008) and thus, in my opinion, if the woman expects sexual intercourse to be as good as a prior experience, they're more likely to desire it more.
So, perhaps deprivation or excess of sexual intercourse and expectancies of quality of sexual intercourse plays a major role in moulding sexual desire for women. Another thing: while the frequency of sex is predicated on the physical rewards of it for men, this may not be necessarily true for women.

References

Willoughby, B.J. & Vitas, J. (2012). Sexual desire frequency: The effect of individual differences in desired and actual sexual frequency on dating couples. Archive of Sexual Behavior, 41, 477-486.
McNulty, J.K. & Fisher, T.D. (2008). Gender differences in response to sexual expectancies and changes in sexual frequency: A short-term longitudinal study of sexual satisfaction in newly married couples. Archive of Sexual Behavior, 37, 229-240.