Higher Cortical Functions

What is a higher cortical function? As one examines the abilities of a human, one is struck by our ability to use tools and create wonderful buildings or works of art. However, our ability to communicate by speaking and writing and reading, we believe, is the best example of a higher cortical function. These centers that are responsible for language are primarily in the dominant hemisphere. The motor type of aphasia (Broca’s area) originates from damage to the inferior frontal gyrus whereas the sensory type of aphasia originates from damage to the superior temporal gyrus (Wernicke’s area).

It is well to warn the student beginning the study of language function that prior to the development of modern neuroimaging this had been an area of much confusion, with much disagreement and multiple hypotheses. This discussion will be limited to the more practical problems of anatomical localization.

Dysarthria refers to a difficulty in articulation of speech from weakness or paralysis or from mechanical difficulties and it is not related to a problem in the cerebral cortex but to disease in the lower motor neurons or the muscles that control the production of speech or to a lesion in the corticobulbar pathway. In this chapter we will discuss language dysfunction due to lesions in the cerebral cortex and introduce the following terms: aphasia, apraxia, and dyslexia.