Instruct: Given a question, retrieve passages that can help answer the question.
Query: What area of the cortex controls speech?
Language processing has been linked to Broca's area since Pierre Paul Broca reported impairments in two patients. They had lost the ability to speak after injury to the posterior inferior frontal gyrus (pars triangularis) (BA45) of the brain. Since then, the approximate region he identified has become known as Broca's area, and the deficit in language production as Broca's aphasia, also called expressive aphasia. Broca's area is now typically defined in terms of the pars opercularis and pars triangularis of the inferior frontal gyrus, represented in Brodmann's cytoarchitectonic map as Brodmann area 44 and Brodmann area 45 of the dominant hemisphere.
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.
The role of statistical learning in language acquisition has been particularly well documented in the area of lexical acquisition. One important contribution to infants' understanding of segmenting words from a continuous stream of speech is their ability to recognize statistical regularities of the speech heard in their environments. Although many factors play an important role, this specific mechanism is powerful and can operate over a short time scale.
Neuroplasticity is defined as the brain's ability to reorganize itself, lay new pathways, and rearrange existing ones, as a result of experience. Neuronal changes after damage to the brain such as collateral sprouting, increased activation of the homologous areas, and map extension demonstrate the brain's neuroplastic abilities. According to Thomson, "Portions of the right hemisphere, extended left brain sites, or both have been shown to be recruited to perform language functions after brain damage. All of the neuronal changes recruit areas not originally or directly responsible for large portions of linguistic processing. Principles of neuroplasticity have been proven effective in neurorehabilitation after damage to the brain. These principles include: incorporating multiple modalities into treatment to create stronger neural connections, using stimuli that evoke positive emotion, linking concepts with simultaneous and related presentations, and finding the appropriate intensity and duration of treatment for each individual patient.
Broca's (expressive) aphasia is a type of non-fluent aphasia in which an individual’s speech is halting and effortful. Misarticulations or distortions of consonants and vowels, namely phonetic dissolution, are common. Individuals with expressive aphasia may only produce single words, or words in groups of two or three. Long pauses between words are common and multi-syllabic words may be produced one syllable at a time with pauses between each syllable. The prosody of a person with Broca's aphasia is compromised by shortened length of utterances and the presence of self-repairs and disfluencies. Intonation and stress patterns are also deficient.
Each patient that suffers from apperceptive agnosia does not have brain damage in exactly the same area. However, brain damage in proximity to the occipital lobe is largely correlated with the patterns of deficit seen in apperceptive agnosics. For example, patient JB suffered extensive damage to the parietal-occipital areas to the left cerebral hemisphere leading to his deficit in the ability to name distinguish between structurally similar object.
Damage to the left hemisphere of the brain has been explicitly implicated in the associative form of visual agnosia. Goldberg suggested that the associative visual form of agnosia results from damage to the ventral stream of the brain, the occipito-temporal stream, which plays a key role in object recognition as the so-called "what" region of the brain, as opposed to the "where," dorsal stream.
When discussing the time period where children begin to speak, Bates received a lot of attention for finding an overwhelming amount of nouns within the first 50 words of a native English speaker's vocabulary. Bates helped settle an ongoing debate among linguists who argued that a referential language style, characterized by the child's first 50 words containing mostly object labels, was a better strategy in developing language than a personal and socially expressive language style. She found that regardless of the strategy applied by the child, they learn words at the same rate. She did, however, find strong predictive power in the child’s vocabulary at 13 and 20 months old and their grammatical complexity at 2 years old. Bates finds that language learning comes from the neural plasticity in the brain; therefore, children can and are able to learn a language, even with brain trauma.
Research in her lab also showed that adult aphasic patients' deficits were not specific to linguistic structures theorized to be localized to specific brain areas, nor were they restricted to the linguistic domain. Lesion sites overlap in the role that they affect speech fluency and complexity. Language is dependent upon basic cognitive processes such as memory, pattern recognition, and spreading activation. This perspective runs counter to the theory of Noam Chomsky, Eric Lenneberg, and Steven Pinker that language is a special stimulus that is processed by specific language modules in the mind such as the localization to the Broca's and Wernicke's areas.
Neuroimaging research has supported this view, demonstrating specific brain regions consistently engaged during theory of mind tasks. PET research on theory of mind, using verbal and pictorial story comprehension tasks, has identified a set of brain regions including the medial prefrontal cortex (mPFC), and area around posterior superior temporal sulcus (pSTS), and sometimes precuneus and amygdala/temporopolar cortex. Subsequently, research on the neural basis of theory of mind has diversified, with separate lines of research focused on the understanding of beliefs, intentions, and more complex properties of minds such as psychological traits.
There are dozens of other chemical neurotransmitters that are used in more limited areas of the brain, often areas dedicated to a particular function. Serotonin, for example—the primary target of antidepressant drugs and many dietary aids—comes exclusively from a small brainstem area called the raphe nuclei. Norepinephrine, which is involved in arousal, comes exclusively from a nearby small area called the locus coeruleus. Other neurotransmitters such as acetylcholine and dopamine have multiple sources in the brain, but are not as ubiquitously distributed as glutamate and GABA.
Neuroimaging also uncovered different sub-regions in the anterior cingulate cortex itself based on their function. These studies showed that the caudal part of the anterior cingulate cortex plays a more important function in cognitive activities that involve attention, salience, interference and response competition. These results combined with electrophysiological investigation of the function of neurons in the anterior cingulate cortex have provided insights that can be used in the improvement of cingulotomy performed on patients treated for OCD. The basis behind this idea is the fact that a variation of certain tasks, Emotional Stroop tasks (ES), which have been particularly identified as exerting effects in OCD patients activate neurons in the more rostral part of the anterior cingulate cortex. Thus, theoretically if bilateral cingulotomy is performed in such patient in the rostral anterior cingulate cortex, better results should be obtained.
In a review of the role of distributional learning on phonological acquisition, Werker et al. note that distributional learning cannot be the only mechanism by which phonetic categories are acquired. However, it does seem clear that this type of statistical learning mechanism can play a role in this skill, although research is ongoing.
Functional MRI analyses of the anterior cingulate cortex have also led to the introduction of bilateral cingulotomy for the treatment of chronic pain. Such application was introduced since the anterior cingulate cortex has been found to be related to the processing nociceptive information input. In particular the role of the anterior cingulate cortex is in the interpretation of how a stimulus affects a person rather than its actual physical intensity.
Thewissen’s current work involves counting neurons in bowhead and beluga whale brain samples, to assess brain function, in Utqiagvik—formerly Barrow—Alaska. Though the size of the brains of sperm whales and killer whales are larger than those of any other organism, including humans, a better measure of brain function is to determine how many neurons there are in the brain. Suzana Herculano-Houzel has developed a method of counting of neurons of human and other animals' brains and the relation between the cerebral cortex area and thickness and number of cortical folds. Humans and other primates pack about twice the number of neurons in a cubed inch of brain as most other mammals.
The cingulum is described from various brain images as a C shaped structure within the brain that wraps around the frontal lobe to the temporal lobe right above the corpus callosum. It is located beneath the cingulate gyrus within the medial surface of the brain therefore encircling the entire brain. There are two primary parts of the cingulate cortex: the posterior cingulate cortex and the anterior cingulate cortex. The anterior is linked to emotion, especially apathy and depression. Here function and structure changes are related meaning any change within this structure would lead to a function change, particularly behavioral because of its function involving emotions. Damage to this area can have various effects on mental disorders and mental health. The posterior section is more related to cognitive functions. This can include attention, visual and spatial skills, working memory and general memory. Because of its location, the cingulum is very important to brain structure connectivity and the integration of information that it receives.
Dopaminergic neurons (dopamine-producing nerve cells) are comparatively few in number—a total of around 400,000 in the human brain—and their cell bodies are confined in groups to a few relatively small brain areas. However their axons project to many other brain areas, and they exert powerful effects on their targets. These dopaminergic cell groups were first mapped in 1964 by Annica Dahlström and Kjell Fuxe, who assigned them labels starting with the letter "A" (for "aminergic"). In their scheme, areas A1 through A7 contain the neurotransmitter norepinephrine, whereas A8 through A14 contain dopamine. The dopaminergic areas they identified are the substantia nigra (groups 8 and 9); the ventral tegmental area (group 10); the posterior hypothalamus (group 11); the arcuate nucleus (group 12); the zona incerta (group 13) and the periventricular nucleus (group 14).
Theta waves are used to measure activity in mainly the hippocampus but can be used to measure other brain regions as well. Strong synchronization of theta waves in the hippocampus and anterior ventral thalamus has been observed. Although theta waves between the hippocampus and the anterior dorsal and anterior medial regions in the thalamus showed no synchronization, scientists have seen a marked increase in firing rates of the neurons in the brain regions. Overall, based on theta wave experimentation, some components of the Papez circuit have shown to indeed have a connection and work together. Also, theta waves are thought to be linked to learning and memory. Consequently, many scientists believe that the Papez circuit is involved with memory because of theta wave experiments. Some scientists have narrowed it down to specifically spatial and episodic memory.
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.
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.
As such, artificial language experiments are typically conducted to explore what the relevant linguistic variables are, what sources of information infants are able to use and when, and how researchers can go about modeling the learning and acquisition process. Aslin and Newport, for example, have used artificial languages to explore what features of linguistic input make certain patterns salient and easily detectable by infants, allowing them to easily contrast the detection of syllable repetition with that of word-final syllables and make conclusions about the conditions under which either feature is recognized as important.
Some language acquisition researchers, such as Elissa Newport, Richard Aslin, and Jenny Saffran, emphasize the possible roles of general learning mechanisms, especially statistical learning, in language acquisition. The development of connectionist models that are able to successfully learn words and syntactical conventions supports the predictions of statistical learning theories of language acquisition, as do empirical studies of children's detection of word boundaries. In a series of connectionist model simulations Franklin Chang has demonstrated that such domain general statistical learning mechanism could explain a wide range of language structure acquisition phenomena.
The prefrontal cortex is located in the most anterior portion of the frontal lobe in the brain. It forms a larger portion of the cortex in humans. The dendrites in the prefrontal cortex contain up to 16 times as many dendritic spines as neurons in other cortical areas. Due to this, the prefrontal cortex integrates a large amount of information. The orbitofrontal cortex cells are important factors for self-control. If an individual has the choice between an immediate reward or a more valuable reward which they can receive later, an individual would most likely try to control the impulse to take that immediate reward. If an individual has a damaged orbitofrontal cortex, this impulse control will most likely not be as strong, and they may be more likely to take the immediate reinforcement. Additionally, we see lack of impulse control in children because the prefrontal cortex develops slowly.
The primary auditory cortex is surrounded by secondary auditory cortex, and interconnects with it. These secondary areas interconnect with further processing areas in the superior temporal gyrus, in the dorsal bank of the superior temporal sulcus, and in the frontal lobe. In humans, connections of these regions with the middle temporal gyrus are probably important for speech perception. The frontotemporal system underlying auditory perception allows us to distinguish sounds as speech, music, or noise.
New medical imaging techniques such as PET and fMRI have allowed researchers to generate pictures showing which areas of a living brain are active at a given time. In the past, research was primarily based on observations of loss of ability resulting from damage to the cerebral cortex. Indeed, medical imaging has represented a radical step forward for research on speech processing. Since then, a whole series of relatively large areas of the brain have been found to be involved in speech processing. In more recent research, subcortical regions (those lying below the cerebral cortex such as the putamen and the caudate nucleus) as well as the pre-motor areas (BA 6) have received increased attention. It is now generally assumed that the following structures of the cerebral cortex near the primary and secondary auditory cortices play a fundamental role in speech processing:The left hemisphere is usually dominant in right-handed people, although bilateral activations are not uncommon in the area of syntactic processing. It is now accepted that the right hemisphere plays an important role in the processing of suprasegmental acoustic features like prosody.
Studies using computational modeling and functional magnetic resonance imaging (fMRI) have shown that the temporo-parietal regions function as a conscious self-monitoring system to support an automatic speech production system and that projections from auditory error cells in the posterior superior temporal cortex that go to motor correction cells in right frontal cortex mediate auditory feedback control of speech.