DIFFERENTIAL PROPERTIES OF CELLS IN THE FELINE PRIMARY VISUAL-CORTEX PROVIDING THE CORTICOFUGAL FEEDBACK TO THE LATERAL GENICULATE-NUCLEUS AND VISUAL CLAUSTRUM

We have examined the responses of 141 layer VI cells in the feline vis ual cortex, Within this group we compared the responses of a subpopula tion of cells checked for connectivity by electrical stimulation in th e dLGN and the visual claustrum, The antidromically identified cortico geniculate projecting cells had relatively short receptive fields, as judged from length response curves, measured quantitatively, and were located at the ''short'' end of the receptive field length spectrum se en in the general population, Of the 17 corticogeniculate projecting c ells, 71% were S type cells, which were typically monocular and direct ionally selective, with relatively long latencies following electrical stimulation, The remaining 29% were C type cells, also directionally selective, but with a wider spread of ocular dominance preferences and shorter latencies following electrical stimulation, S and C type subp opulations did not differ in their receptive field lengths. The mean r eceptive field length for this subpopulation was 2.2 degrees +/- 0.27, the shortest field being 1 degrees and the longest 5 degrees, The fiv e layer VI cells activated by electrical stimulation from electrodes w ithin the dorsocaudal (visual) claustrum all had much longer receptive field lengths than the corticogeniculate population, often 10 degrees or longer and were monocular and directionally selective S type cells , These data indicate that the information carried in the corticogenic ulate stream (and that from layer VI directly to layer IV carried by a xon collaterals) is relatively tightly focused in spatial terms whilst the less spatially focused, long receptive field output from layer VI projects to the claustrum.