Instruct: Given a question, retrieve documents that answer the question.
Query: How long can amnesia last?
Amnesia is a deficit in memory caused by brain damage, disease, or psychological trauma. Amnesia can also be caused temporarily by the use of various sedatives and hypnotic drugs. The memory can be either wholly or partially lost due to the extent of damage that was caused. There are two main types of amnesia: retrograde amnesia and anterograde amnesia. Retrograde amnesia is the inability to retrieve information that was acquired before a particular date, usually the date of an accident or operation. In some cases the memory loss can extend back decades, while in others the person may lose only a few months of memory. Anterograde amnesia is the inability to transfer new information from the short-term store into the long-term store. People with this type of amnesia cannot remember things for long periods of time. These two types are not mutually exclusive; both can occur simultaneously.
Studies on specific cases demonstrate how particular impaired areas of the hippocampus are associated with the severity of RA. Damage can be limited to the CA1 field of the hippocampus, causing very limited RA for about 1 to 2 years. More extensive damage limited to the hippocampus causes temporally graded amnesia for 15 to 25 years. Another study also suggests that large medial temporal lobe lesions, that extend laterally to include other regions, produce more extensive RA, covering 40 to 50 years. These findings suggest that density of RA becomes more severe and long-term as the damage extends beyond the hippocampus to surrounding structures.
While short-term memory encodes information acoustically, long-term memory encodes it semantically: Baddeley (1966) discovered that, after 20 minutes, test subjects had the most difficulty recalling a collection of words that had similar meanings (e.g. big, large, great, huge) long-term. Another part of long-term memory is episodic memory, "which attempts to capture information such as 'what', 'when' and 'where. With episodic memory, individuals are able to recall specific events such as birthday parties and weddings.
Memory has typically been divided into sensory, short term, and long term processes. According to Rasmuseen & Berntsen, 2009, "long-term memory processes may form the core of spontaneous thought". Thus the memory process most related to flashbacks is long term memory. As well, studies by Rasmuseen & Berntsen, 2009, have shown that long term memory is also susceptible to extraneous factors such as recency effect, arousal and rehearsal as it pertains to accessibility. Compared to voluntary memories, involuntary memories show shorter retrieval times and little cognitive effort. Finally, involuntary memories arise due to automatic processing, which does not rely on higher-order cognitive monitoring, or executive control processing. Voluntary memory is normally associated with contextual information, which is what allows for correspondence between time and place, this is not true of flashbacks. According to Brewin, Lanius et, al, 2009, flashbacks, are disconnected from contextual information, and as a result are disconnected from time and place.
Memory is divided into voluntary (conscious) and involuntary (unconscious) processes that function independently of each other. Theories and research on memory dates back to Hermann Ebbinghaus, who began studying nonsense syllables. Ebbinghaus classified three distinct classes of memory: sensory, short term, and long-term memory. Sensory memory is made up of a brief storage of information within a specific medium (the line you see after waving a sparkler in your field of vision is created by sensory memory). Short term memory is made up of the information currently in use to complete the task at hand. Long term memory is composed of the systems used to store memory over long periods. It enables one to remember what happened two days ago at noon, or who called last night.
The neuroscientist Donald Hebb (1904–1985) was the first to distinguish between short-term memory and long-term memory. According to current theories in neuroscience, things that we "notice" are stored in short-term memory for up to a few minutes; this memory depends on "reverberating" electrical activity in neuronal circuits, and is very easily destroyed by interruption or interference. Memories stored for longer than this are stored in "long-term memory". Whether information is stored in long-term memory depends on its "importance"; for any animal, memories of traumatic events are potentially important for the adaptive value that they have for future avoidance behavior, and hormones that are released during stress have a role in determining what memories are preserved. In humans, traumatic stress is associated with acute secretion of epinephrine and norepinephrine (adrenaline and noradrenaline) from the adrenal medulla and cortisol from the adrenal cortex. Increases in these facilitate memory, but chronic stress associated with prolonged hypersecretion of cortisol may have the opposite effect. The limbic system is involved in memory storage and retrieval as well as giving emotional significance to sensory inputs. Within the limbic system, the hippocampus is important for explicit memory, and for memory consolidation; it is also sensitive to stress hormones, and has a role in recording the emotions of a stressful event. The amygdala may be particularly important in assigning emotional values to sensory inputs.
Even when childhood events are not remembered episodically, they can be implicitly remembered. Humans can be primed and implicitly trained earlier before they can remember facts or autobiographical events. This is most important in terms of emotional trauma. Adults can generally recall events from 3–4 years old, and have primarily experiential memories beginning around 4.7 years old. However, some suggest that adults who had traumatic and abusive early childhoods report an offset of childhood amnesia around 5–7 years old. It has been suggested that this is because stressful experiences can injure memory centers and possibly make it harder to form memories. This coupled with the fact that priming can occur at a younger age may indicate that children in abusive situations have implicit memory connections that were formed in response to the abuse. Whether or not these 'repressed' memories can affect individuals is a matter of considerable debate in psychology.
Short-term memory is supported by transient patterns of neuronal communication, dependent on regions of the frontal lobe (especially dorsolateral prefrontal cortex) and the parietal lobe. Long-term memory, on the other hand, is maintained by more stable and permanent changes in neural connections widely spread throughout the brain. The hippocampus is essential (for learning new information) to the consolidation of information from short-term to long-term memory, although it does not seem to store information itself. It was thought that without the hippocampus new memories were unable to be stored into long-term memory and that there would be a very short attention span, as first gleaned from patient Henry Molaison after what was thought to be the full removal of both his hippocampi. More recent examination of his brain, post-mortem, shows that the hippocampus was more intact than first thought, throwing theories drawn from the initial data into question. The hippocampus may be involved in changing neural connections for a period of three months or more after the initial learning.
Researchers have investigated the relationship between posttraumatic amnesia (PTA) resulting from traumatic brain injury (TBI) and the development of symptoms of posttraumatic stress disorder (PTSD) and acute stress disorder (ASD). 282 outpatients, who were an average of 53 days post-TBI in their recovery, were divided into four groups: PTA episode lasting less than one hour; PTA episode lasting between one hour and 24 hours; PTA episode lasting between 24 hours and one week; and PTA episode lasting for longer than one week. The patients' personal details were used as variables classified for age, gender, marital status, time elapsed between injury and assessment, and type of injury (motor vehicle accident, pedestrian, assault and other). Patients were given two self-report inventories: the Impact of Event Scale (IES) and the General Health Questionnaire (GHQ). The IES measures symptoms of PTSD and contains questions regarding the intrusiveness of the traumatic event (ex. nightmares) and avoidant behaviours related to the traumatic event (ex. avoiding a certain location). The GHQ was used as an indicator of overall psychological health. The majority of subjects were in Group 1 (PTA episode lasting less than one hour), injured in motor vehicle accidents, and male.
Agnosia is the inability to process sensory information. Often there is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss. It is usually associated with brain injury or neurological illness, particularly after damage to the occipitotemporal border, which is part of the ventral stream. Agnosia only affects a single modality, such as vision or hearing. More recently, a top-down interruption is considered to cause the disturbance of handling perceptual information.
Agnosia is the inability to recognize certain objects, persons or sounds. Agnosia is typically caused by damage to the brain (most commonly in the occipital or parietal lobes) or from a neurological disorder. Treatments vary depending on the location and cause of the damage. Recovery is possible depending on the severity of the disorder and the severity of the damage to the brain. Many more specific types of agnosia diagnoses exist, including: associative visual agnosia, astereognosis, auditory agnosia, auditory verbal agnosia, prosopagnosia, simultanagnosia, topographical disorientation, visual agnosia etc.
Post-concussion syndrome, also known as postconcussive syndrome or PCS, is a set of symptoms that may continue for weeks, months, or a year or more after a concussion – a mild form of traumatic brain injury (TBI). The rates of PCS vary, but most studies report that about 15% of individuals with a history of a single concussion develop persistent symptoms associated with the injury. A diagnosis may be made when symptoms resulting from concussion last for more than three months after the injury. Loss of consciousness is not required for a diagnosis of concussion or post-concussion syndrome.
Agnosia is "the loss or diminution of the ability to recognize familiar objects or stimuli usually as a result of brain damage". There are several different kinds of agnosia that affect every one of our senses, but the two most common related to speech are speech agnosia and phonagnosia.
John finds that his son is still alive but suffers from Alzheimer's disease and is in a nursing home, with no children to help look after him. Assisted by Jack Harkness, John visits his son, who barely remembers John's presence. John becomes very remorseful at missing his son's life and being unable to adapt to modern times.
Anders Ericsson and Walter Kintsch have introduced the notion of "long-term working memory", which they define as a set of "retrieval structures" in long-term memory that enable seamless access to the information relevant for everyday tasks. In this way, parts of long-term memory effectively function as working memory. In a similar vein, Cowan does not regard working memory as a separate system from long-term memory. Representations in working memory are a subset of representations in long-term memory. Working memory is organized into two embedded levels. The first consists of long-term memory representations that are activated. There can be many of these—there is theoretically no limit to the activation of representations in long-term memory. The second level is called the focus of attention. The focus is regarded as having a limited capacity and holds up to four of the activated representations.
The prevalence of phantom pain in upper limb amputees is nearly 82%, and in lower limb amputees is 54%. One study found that eight days after amputation, 72% of patients had phantom limb pain, and six months later, 67% reported it. Some amputees experience continuous pain that varies in intensity or quality; others experience several bouts of pain per day, or it may reoccur less often. It is often described as shooting, crushing, burning or cramping. If the pain is continuous for a long period, parts of the intact body may become sensitized, so that touching them evokes pain in the phantom limb. Phantom limb pain may accompany urination or defecation.
Phantom limb sensation is any sensory phenomenon (except pain) which is felt at an absent limb or a portion of the limb. It has been known that at least 80% of amputees experience phantom sensations at some time of their lives. Some experience some level of this phantom pain and feeling in the missing limb for the rest of their lives.
In 1974 Baddeley and Hitch proposed an alternative theory of short-term memory: Baddeley's model of working memory. According to this theory, short-term memory is divided into different slave systems for different types of input items, and there is an executive control supervising what items enter and exit those systems. The slave systems include the phonological loop, the visuo-spatial sketchpad, and the episodic buffer (later added by Baddeley).
All drugs and stimulants of the brain can affect how someone learns, consolidates, and retrieves certain memories. For example, cocaine blocks the reuptake of dopamine, a neurotransmitter in the brain, causing an increase of dopamine in the synaptic cleft. This will elicit a rewarding feeling of liberation and security that can become addictive to some people. Although, because of the increased dopamine levels in the brain, consolidation of memory can be affected which will then inhibit the chances of recovering that memory. Studies show that rats who were given cocaine were unable to perform motor tasks as successfully as the control group. Also, cannabis has also shown negative effects regarding the ability to spontaneously recover memories because the plasticity strength of the initial memories are so inhibited due to the reduced neurotransmitters in the synaptic cleft.
Duration of PTA may be difficult to gauge accurately; it may be overestimated (for example, if the patient is asleep or under the influence of drugs or alcohol for part of the time) or underestimated (for example, if some memories come back before continuous memory is regained). The Galveston Orientation and Amnesia Test (GOAT) exists to determine how oriented a patient is and how much material they are able to recall.
The GOAT is the most widely used standardized scale for the prospective assessment of PTA in the United States and Canada. The test is made up of 10 items that assess orientation and recollection of the events before and after the injury. It can be used to assess the duration of PTA; this particular GOAT assessment has been found to strongly predict functional outcome as measured by the Glasgow Outcome Scale, return to productivity, psychosocial function and distress.
Obsessive-compulsive individuals have difficulty forgetting unwanted thoughts. When they encode this information into memory they encode it as a neutral or positive thought. This is inconsistent with what a person without OCD would think about this thought, leading the individual with OCD to continue displaying their specific "ritual" to help deal with their anxiety. When asked to forget information they have encoded, OCD patients have difficulty forgetting what they are told to forget only when the subject is negative. Individuals not affected by OCD do not show this tendency. Researchers have proposed a general deficit hypothesis for memory related problems in OCD. There are limited studies investigating this hypothesis. These studies propose that memory is enhanced for menacing events that have occurred during the individuals life. For example, a study demonstrated that individuals with OCD exhibit exceptional recall for previously encountered events, but only when the event promoted anxiety in the individual.
For practical purposes, organizational memory (OM) can be broken down into three distinct time frames. Short-term OM lasts up to about five years; medium-term OM occupies a time frame of up to around ten years, with periods in excess of this constituting long-term OM. Typically existing only in the minds of individuals, it is normally very difficult to share and to capture. Because of its contemporary and contiguous nature, short- and medium-term OM is generally more relevant to operational issues facing the organization, whilst long-term OM is more conformant with strategy and culture.
Anterograde amnesia is a loss of the ability to create new memories after the event that caused amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact. This is in contrast to retrograde amnesia, where memories created prior to the event are lost while new memories can still be created. Both can occur together in the same patient. To a large degree, anterograde amnesia remains a mysterious ailment because the precise mechanism of storing memories is not yet well understood, although it is known that the regions involved are certain sites in the temporal cortex, especially in the hippocampus and nearby subcortical regions.
Post-traumatic amnesia (PTA) is a state of confusion that occurs immediately following a traumatic brain injury (TBI) in which the injured person is disoriented and unable to remember events that occur after the injury. The person may be unable to state their name, where they are, and what time it is. When continuous memory returns, PTA is considered to have resolved. While PTA lasts, new events cannot be stored in the memory. About a third of patients with mild head injury are reported to have "islands of memory", in which the patient can recall only some events. During PTA, the patient's consciousness is "clouded". Because PTA involves confusion in addition to the memory loss typical of amnesia, the term ""post-traumatic confusional state"" has been proposed as an alternative.
There have been assertions of a possible link between TGA and the use of statins (a class of drug used in treating cholesterol).
En bloc memory loss which is total, permanent, and irrecoverable can occur as an alcoholic "black out," usually lasting longer than an hour and up to 2–5 days.
Marijuana intoxication, Halogenated hydroxyquinolines such as Clioquinol, PDE inhibitors such as sildenafil, Digitalis and scopolamine intoxication, and general anaesthesia have been reported with TGA.
A differential diagnosis should include:
If the event lasts less than one hour, transient epileptic amnesia (TEA) might be implicated.