The brain's language areas, pragmatics, hemineglect, anosognosia, and prosody—the importance of both left and right hemisphere function:
In most humans, especially right-handed humans, specialized cortical language areas are located in the brain's left hemisphere. In many left-handed people, however, specialized cortical language areas exist in both hemispheres. A minority of both left- and right-handed people appear to have specialized cortical areas for language in only the right hemisphere. Wikipedia aptly describes the brain's plasticity: "Studies of children have shown that if a child has damage to the left hemisphere, the child may develop language in the right hemisphere instead. The younger the child, the better the recovery. So, although the 'natural' tendency is for language to develop on the left, human brains are capable of adapting to difficult circumstances, if the damage occurs early enough."
The Canadian Institute of Neurosciences, Mental Health and Addiction, and the Canadian Institutes of Health Research, provides the image to the left, which links to an educational module, The Brain from Top to Bottom. The particular module to which this image links provides a good overview of Paul Broca and Carl Wernicke, two nineteenth-century neuroanatomists who, during autopsies, studied the brains of people who had suffered from language disorders during their lives. Broca and Wernicke were thus able to correlate damage to specific areas with language deficits. Two specific areas now bear the scientists' names.
Subsequent brain imaging experiments have revealed a third region of the brain—the inferior parietal lobule—that large bundles of nerve fibers connect to both Broca's area and Wernicke's area. (It should be noted here that the term lobule generally means a smaller subdivision of the larger lobe.) The inferior parietal lobule, also known as Geschwind's Territory, is named for American neurologist Norman Geschwind (1926-1984) who called attention to its importance. The image to the right links to an intermediate-level module in The Brain from Top to Bottom that sums up the important role of this area: "The inferior parietal lobule of the left hemisphere lies at a key location in the brain, at the junction of the auditory, visual, and somatosensory cortexes, with which it is massively connected. In addition, the neurons in this lobule have the particularity of being multimodal, which means that they can process different kinds of stimuli (auditory, visual, sensorimotor, etc.) simultaneously. This combination of traits makes the inferior parietal lobule an ideal candidate for apprehending the multiple properties of spoken and written words: their sound, their appearance, their function, etc. This lobule may thus help the brain to classify and label things, which is a prerequisite for forming concepts and thinking abstractly."
The image to the left is also taken from the intermediate-level module of The Brain from Top to Bottom (image links to source). This module explains that the left hemisphere controls the "phonological, syntactic, and lexical aspects" of conversation. This explains why the left hemisphere was long considered the dominant hemisphere for language. The left hemisphere is not, however, solely responsible for communication and the module goes on to explain the role of the right hemisphere. "The contributions of the right hemisphere to language behaviour are more subtle and nuanced and were not recognized until much later on. The right hemisphere provides the ability to go beyond the literal meanings of words and employs multiple processes to do so. The new science of communication from the perspective of the 'minor hemisphere' for language is called pragmatics."
The pragmatic function, for example, allows one to "understand things that are implicitly signified in discourse—for example, the meanings of metaphors, or of questions like 'Do you have a light?' When right-handed people suffer damage to the right hemisphere of the brain, this pragmatic function is affected, and they tend to interpret such metaphors and questions literally. In fact, these people react exactly as if they were dealing with idioms in a foreign language: their grammar and phonology may be correct, but they do not understand the verbal humour or metaphors that native speakers of that language use every day. Thus, by contributing to the emotional and tonal components of language, the right hemisphere infuses verbal communication with additional meanings."
Damage to the right hemisphere illustrates its vital role in communication as well as the complex connectedness of the brain. The image to the right—taken while the subject was generating words—links to an advanced-level module of The Brain from Top to Bottom. This module explains that right-hemisphere damage can result in hemineglect, in which one pays no attention to stimuli coming in from the left side of the body.
In anosognosia, which Damasio discusses in Descartes' Error, an individual cannot recognize certain parts of their body as being their own. "Anosognosia, as the condition is known, is one of the most eccentric neuropsychological presentations one is likely to encounter. The wordÑwhich derives from the greek nosos, 'disease,' and gnosis, 'knowledge'–denotes the inability to acknowledge disease in oneself." Damasio writes: "No less dramatic than the oblivion that anosognosic patients have regarding their sick limbs is the lack of concern they show for their overall situation, the lack of emotion they exhibit, the lack of feeling they report when questioned about it. … Patients with the type of anosognosia described above have damage in the right hemisphere. Although drawing up a full characterization of the neuroanatomical correlates of anosognosia is an ongoing project, this much is apparent: There is damage to a select group of right cerebral cortices which are known as somatosensory (from the Greek root soma, for body; the somatosensory system is responsible for both the external senses of joint position, visceral state, and pain) and which include the cortices in the insula; the cytoarchitectonic areas 3, 1, 2 (in the parietal region); and area S2 (also parietal, in the depth of the sylvian fissure)."
Right-hemisphere damage also can affect an individual's use of prosody, which is the ability to use intonation and stress to convey the emotions one feels. Afflicted individuals therefore communicate in a way that seems flat and emotionless.
In Brainscapes, Restak illuminates what happens when the language-processing left hemisphere is taken out of the loop. "When J.W., a split-brain patient of neuropsychologist Michael Gazzaniga, is shown for less than a second a picture of a horse flashed only to his right hemisphere, he denies that he has seen anything. But when asked to draw 'what goes on it,' he picks up a pencil with his left hand and draws an English saddle, a rather primitive drawing difficult to interpret outside of the context of the experiment. The patient doesn't recognize what he has drawn. He is then asked to draw, rather than say, what picture has been flashed. With his left hand he then draws a horse and, after completing the picture, he grins and says of the first drawing: 'That must be a saddle.'"
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