Abstract
It is commonly believed that orientation selectivity first emerges in the primary visual cortex (V1). In the present study, first, we examined the orientation selectivity of LGN neurons using optimal and non-optimal (in terms of stimulus size and spatial frequency (SF)) grating stimuli in anesthetized cats. We found that although only about 10% LGN neurons showed significantly orientation-biased response to the grating with optimal size and SF, about 90% of LGN neurons exhibited significant orientation selectivity to grating with diameters larger than its classical receptive field (CRF) and SFs higher than the optimal for CRF response. Then, stimulus-size tuning curves were made for responses to stimulation with preferred orientation tested with large stimulus and with orthogonal orientation. These two stimulus-size tuning curves exhibited profile similar to each other under the optimal SF condition. However, high SF grating caused stronger surround suppression for response to the orthogonally oriented stimulus than that to the optimally orientated stimulus. These results suggest that there is orientation tuned surround suppression that is effective around the CRF boundary and its optimal SF is tuned to higher than that of the CRF responses. We should further address how the orientation selectivity of LGN contributes to that in V1. [J Physiol Sci. 2006;56 Suppl:S176]
