Brain function: changing ideas on the role of sensory, motor, and association cortex in behavior.

The classical three-way subdivision of cerebral neocortex into sensory, motor, and association areas is the product of a convergence of experimental and clinical evidence over almost a century (cf. 203). However, in the last 20 years, evidence difficult to reconcile with this idea has begun to accumulate. For example, we now know that neural activity in sensory cortex does not just mirror receptor activity, nor is motor cortex the "keyboard of the mind." Furthermore, we know that association takes place both in animals with little or no association cortex and in animals in which the normal complement of association cortex has been surgically removed (e.g. 235, 236, 333, 334). Because of these obvious difficulties with the classical view, it seemed worthwhile to review the main lines of inquiry that have tended to demand a more sophisticated view of the contribution of the various areas of cerebral neocortex. However, to provide a format that is easy to follow, we have retained the classical distinctions as the basis for subdividing the review itself. Therefore, there are six main sections dealing respectively with visual, auditory, and somatosensory cortex, motor cortex, and finally posterior and frontal association cortex. Each of these sections has been further divided along methodological lines (i.e. anatomy, physiology, and behavior).