ORIENTATIONAL INFLUENCES OF LAYER-V OF VISUAL AREA-18 UPON CELLS IN LAYER-V OF AREA-17 IN THE CAT CORTEX

We examined the orientation tuning curves of 86 cells located in layer V of area 17, before, during, and after focal blockade of a small (30 0-mum diameter) region of near-retinotopic register in layer V of area 18 of quantitatively established orientation preference. Such focal b lockade revealed three distinct populations of area 17 layer V cells-c ells with decreased responses to stimuli of some orientations (21%), c ells with increased responses to stimuli of some orientations (43%), a nd cells unaffected by the focal blockade (36%). These effects were cl ear-cut, reproducible, and generally directly related to the known rec eptive field properties of the cell recorded in area 18 at the center of the zone of blockade. These effects were also analyzed in terms of alterations in orientation bandwidth in the cells in area 17 as a resu lt of the blockade-bandwidth increases (22%) and decreases (24%) were found; however, these changes were essentially unrelated to the measur ed receptive field properties. Inhibitory and excitatory effects were most pronounced when the regions in areas 17 and 18 were of like ocula r dominance and were of similar orientation preference. Inhibitory eff ects (suggesting a normally excitatory input) were most dependent upon the similarity of receptive fields, excitatory effects (suggesting a normally inhibitory input) were less heavily dependent.