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The long-standing controversy about cerebral functions, whether they are diffusely represented in the cerebrum with all parts roughly equivalent, or localized to certain lobes or regions, has been resolved to the satisfaction of most neurologists. Clinicians and physiologists have demonstrated beyond doubt that particular functions are assignable to certain cortical regions. For example, the pre- and postrolandic zones control motor and sensory activities, respectively, the striate occipital zones control visual perception, the superior temporal gyri are auditory, and so on. Beyond these broad correlations, however, there is a notable lack of precision in the cortical localization of many of the behavioral and mental operations described in Chaps. 20 and 21. In particular, of the higher-order functions, such as attention, vigilance, apperception, and analytic and synthetic thinking, none has a precise and predictable anatomy; or, more accurately, the neural systems on which they depend are widely distributed among several regions.

One may inquire into what precisely is meant by cerebral localization. Does it refer to the physiologic function of a circumscribed aggregate of neurons in the cerebral cortex, indicated clinically by a loss of that function (negative symptom) when the neurons in question are paralyzed or destroyed? From what we know of the rich connectivity of all parts of the specialized cortical centers, one must assume that this is only partly the case, in that a lesion in a particular cerebral region, or in the fiber systems with which it is connected, is most closely associated with certain impairments of function. While the clinician operates on the principle of correlation between neurologic signs or syndromes and damage (lesions) in particular regions of the brain, it is readily apparent that certain positive symptoms resulting from the lesion, e.g., the grasping and sucking responses, cannot arise from destroyed neurons but are attributable to the now altered or disinhibited functions of related intact parts of the cerebrum. And how is one to interpret inconsistencies from one case report to another, in which several different functions have been assigned to the same region of the brain and any one region appears to be the anatomic substratum of multiple functions, or in which a particular sign arises from damage in one of several areas? Most who ponder this subject believe that the organization of cerebral function is based on discrete networks of closely interconnected afferent and efferent neurons in several regions of the brain. These networks must be linked by both regional and more widespread systems of fibers. This is especially apparent in the discussion of the anatomy of complex cognitive properties such as intelligence, as described in Chap. 21. Thus, many basic functions are anchored in one cortical region and a lesion there causes loss of a particular ability. This is quite different than the mechanisms required to engage that same function for actual use.

These aspects of cerebral localization—brought out so clearly in the writings of Wernicke, Déjerine, and Liepmann, have been ...

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