Chemoarchitecture of the brain

Abstract

High-amplitude, short-latency, gross evoked potentials may be recorded outside of striate cortex in the cat. Amplitude and latency of early evoked activity to fullfield illumination were studied under chloralose or barbiturate anesthesia. Data from monopolar and bipolar recordings suggest that the high-amplitude area is coextensive with anatomic area 18 (visual II). The short-latency activity in this region survives ablation of contralateral areas 17 and 18, section of the corpus callosum, and lesion of medial and posterior ipsilateral area 17. Lesions in the lateral trilaminar portion of the dorsal lateral geniculate nucleus (LGN) severely diminish this high-amplitude activity. In one cat, mapped 28 days following geniculate lesion, regions of reduced potentials correlated well with areas of dense preterminal degeneration (Nauta). Lesions in the medial portion of LGN have lesser effects. The dense, direct geniculate input to visual II, supported by both anatomical and physiological evidence, should be considered in formulation of models of visual function in the cat.