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Watch the video titled “The Man With Two Brains” to see the neuroscientist Michael Gazzaniga introduce a patient he has worked with for years who has had his corpus callosum cut, separating his two cerebral hemispheres. A few tests are run to demonstrate how this manifests in tests of cerebral function. Unlike normal people, this patient can perform two independent tasks at the same time because the lines of communication between the right and left sides of his brain have been removed. Whereas a person with an intact corpus callosum cannot overcome the dominance of one hemisphere over the other, this patient can. If the left cerebral hemisphere is dominant in the majority of people, why would right-handedness be most common?

The mental status exam

The cerebrum, particularly the cerebral cortex, is the location of important cognitive functions that are the focus of the mental status exam. The regionalization of the cortex, initially described on the basis of anatomical evidence of cytoarchitecture, reveals the distribution of functionally distinct areas. Cortical regions can be described as primary sensory or motor areas, association areas, or multimodal integration areas. The functions attributed to these regions include attention, memory, language, speech, sensation, judgment, and abstract reasoning.

The mental status exam addresses these cognitive abilities through a series of subtests designed to elicit particular behaviors ascribed to these functions. The loss of neurological function can illustrate the location of damage to the cerebrum. Memory functions are attributed to the temporal lobe, particularly the medial temporal lobe structures known as the hippocampus and amygdala, along with the adjacent cortex. Evidence of the importance of these structures comes from the side effects of a bilateral temporal lobectomy that were studied in detail in patient HM.

Losses of language and speech functions, known as aphasias, are associated with damage to the important integration areas in the left hemisphere known as Broca’s or Wernicke’s areas, as well as the connections in the white matter between them. Different types of aphasia are named for the particular structures that are damaged. Assessment of the functions of the sensorium includes praxis and gnosis. The subtests related to these functions depend on multimodal integration, as well as language-dependent processing.

The prefrontal cortex contains structures important for planning, judgment, reasoning, and working memory. Damage to these areas can result in changes to personality, mood, and behavior. The famous case of Phineas Gage suggests a role for this cortex in personality, as does the outdated practice of prefrontal lobectomy.

Read this article to learn about a young man who texts his fiancée in a panic as he finds that he is having trouble remembering things. At the hospital, a neurologist administers the mental status exam, which is mostly normal except for the three-word recall test. The young man could not recall them even 30 seconds after hearing them and repeating them back to the doctor. An undiscovered mass in the mediastinum region was found to be Hodgkin’s lymphoma, a type of cancer that affects the immune system and likely caused antibodies to attack the nervous system. The patient eventually regained his ability to remember, though the events in the hospital were always elusive. Considering that the effects on memory were temporary, but resulted in the loss of the specific events of the hospital stay, what regions of the brain were likely to have been affected by the antibodies and what type of memory does that represent?

The patient was unable to form episodic memories during the events described in the case, so the medial temporal lobe structures might have been affected by the antibodies.

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Watch the video titled “The Man With Two Brains” to see the neuroscientist Michael Gazzaniga introduce a patient he has worked with for years who has had his corpus callosum cut, separating his two cerebral hemispheres. A few tests are run to demonstrate how this manifests in tests of cerebral function. Unlike normal people, this patient can perform two independent tasks at the same time because the lines of communication between the right and left sides of his brain have been removed. Whereas a person with an intact corpus callosum cannot overcome the dominance of one hemisphere over the other, this patient can. If the left cerebral hemisphere is dominant in the majority of people, why would right-handedness be most common?

The left hemisphere of the cerebrum controls the right side of the body through the corticospinal tract. Because language function is largely associated with the dominant hemisphere, the hand with which a person writes will most likely be the one controlled by the left hemisphere.

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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