TESTING FOR DEFECTS OF HIGHER CORTICAL FUNCTION
It is useful to test functions that can be localized to individual brain regions because abnormalities on these tests can help localize a neuroanatomic defect and thereby suggest a specific etiology. Screening for disorders of higher cortical function can be completed within the context of an office visit, whereas extensive examinations can take up to several hours.
Test Language Function. Judge the fluency of the patient’s language. Note whether language is effortful or not, and if there are mistakenly spoken phonemes or mistakes in grammar. Evaluate comprehension by testing the patient’s ability to follow simple or complex commands. Determine whether the patient can repeat, read, write, and name. Some people may express them- selves well and understand what is said, yet still have a language problem. More sensitive approaches that could prove useful in this setting include counting how many animals the patient can name in 1 minute (a test of semantic fluency). In most language is a relatively left brain–mediated cognitive domain, so inability to perform any of these tasks indicates dysfunction of the perisylvian region of the dominant, usually left, cerebral hemisphere.
Test Memory. Memory is often thought of as long versus short term, but these are potentially misleading terms. What is referred to as short-term memory is really memory stored in “buffer” storage, particularly the posterolateral prefrontal cortices. Long-term memory is information stored in the brain “hard drive,” which requires function of the medial temporal structures such as the hippocampus. These different problems can be distinguished by giving the patient information to encode, ensuring that information has entered the buffer memory, and then distracting the patient. Later on, determine if the information is still available to the patient. Good preservation and easy accessing of the information suggests intact memory “retention,” whereas good preservation that requires cueing implies a deficit of “retrieval.”
Test Visual-Spatial Functions. Have the patient draw a clock, house, daisy, or bicycle, and check for organization, angulation, and asymmetry. Also ask the patient to copy a simple design. If the drawings indicate abnormal visual-spatial orientation, the patient may have a lesion in the right cerebral hemisphere.
Test Ability to Concentrate. Ask the patient to recite in reverse a series of numbers or to subtract 7s serially from 100. Also observe the patient’s degree of alertness and orientation, manner of dress, and grooming, and note whether the patient is happy, sad, or indifferent and how he relates to others. Such objective observations are an important part of a complete neurologic examination.
Test Executive Function. Determine whether the patient can shift from one set to another, perform actions in a sequence, think abstractly, and calculate. For example, asking the patient how much money is “two quarters, two dimes, and two nickels” screens several of these skills. Executive dysfunction suggests a lesion of the posterolateral prefrontal cortex, or a dis- connection between this area and other brain regions.