GABA neurons and GABA receptors are conspicuous elements of cerebral cortical organization. They serve to shape the stimulus-response properties of neurons in the sensory areas and undoubtedly play a comparable role in the nonsensory areas as well. Although nonGABAergic local circuit neurons exist in the cerebral cortex, the variety of forms adopted by the GABAergic neurons and their important functional role have served to focus attention on the latter in investigations of local cortical circuitry. In primate noocortex, GABAergic neurons constitute approximately 25–30% of the neuronal population. In addition to their known or postulated functions in shaping neuronal receptive fields and response profiles, some of which are still controversial (Sillito, 1984; Ferstar, 1986), their transmitter, GABA, and the major class of receptor upon which it acts are regulated in an activity-dependent manner even in the adult (Jones, 1990). In this, there is a potential mechanism for the plasticity of representational maps that is demonstrable in somatic sensory, motor, auditory, and visual cortex (Merzenich et al., 1983; Sanes et al., 1988; Robertson and Irvine, 1989; Kaas at al., 1990).

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