CONTRIBUTION OF AREA-17 TO CELL RESPONSES IN THE STRIATE-RECIPIENT ZONE OF THE CATS LATERAL POSTERIOR-PULVINAR COMPLEX

The cat's lateral posterior-pulvinar complex (LP-pulvinar) contains th ree main representations of the visual field. The lateral part of the LP nucleus (LPI or striate-recipient zone) is the only region of these extrageniculate nuclei which receives afferents from the primary visu al cortex. We investigated the contribution of area 17 to the response properties (orientation and spatial frequency tuning functions) of LP I neurons by cooling or lesioning the visual cortex. Responses of 40 L PI cells were studied before, during and after the reversible cooling of the striate cortex. When tested for orientation, a total of 10 unit s out of 28 was affected (36%). For most of these cells (eight of 10), cooling the visual cortex yielded a reduction of the cells' visual re sponses without altering their orientation-selectivity (there was no s ignificant change in the orientation tuning width). For only two cells , inactivation red to an increase in the response amplitude. Also, blo cking the visual cortex never modified the direction-selectivity of LP I cells. When tested for spatial frequency, 12 neurons out of 33 were affected (36%) by the experimental protocol. In most cases, we observe d a reduction in the responses at each spatial frequency tested, with no change in tuning bandwidth. For only three LPI cells, the effects o f inactivation of the visual cortex were restricted to specific spatia l frequencies, altering the profile of the spatial frequency tuning fu nction. In five cats, removing area 17 reduced the proportion of visua l neurons in LPI and the spared visually evoked responses were noticea bly depressed. Despite the reduction in responsiveness, a few LPI rece ptive fields within the cortical scotoma were still sensitive to the o rientation and/or direction of a moving stimulus. This last observatio n suggests that some properties in LPI could be generated either by ci rcuits intrinsic to the LPI or by afferents from extrastriate cortical areas. Overall, these results indicate that projections from the visu al cortex to the striate-recipient zone of the LP-pulvinar complex are mainly excitatory. Despite the strong impact of the area 17 projectio ns, our data suggest that the extrastriate cortex could also play a ro le in the establishment of response properties in the cat's LPI.