STIMULUS DEPENDENCE OF ORIENTATION AND DIRECTION SENSITIVITY OF CAT LGND RELAY CELLS WITHOUT CORTICAL INPUTS - A COMPARISON WITH AREA-17 CELLS

The cortical contribution to the orientation and direction sensitivity of LGNd relay cells was investigated by recording the responses of re lay cells to drifting sinusoidal gratings of varying spatial frequenci es, moving bars, and moving spots in cats in which the visual cortex ( areas 17, 18, 19, and LS) was ablated. For comparison, the spatial-fre quency dependence of orientation and direction tuning of striate corti cal cells was investigated employing the same quantitative techniques used to test LGNd cells. There are no significant differences in the o rientation and direction tuning to relay cells in the LGNd of normal a nd decorticate cats. The orientation and direction sensitivities of co rtical cells are dependent on stimulus parameters in a fashion qualita tively similar to that of LGNd cells. The differences in the spatial-f requency bandwidths of LGNd cells and cortical cells may explain many of their differences in orientation and direction tuning. Although fac tors beyond narrowness of spatial-frequency tuning must exist to accou nt for the much stronger orientation and direction preferences of cell s in area 17 when compared to LGNd cells, the evidence suggests that t he orientation and direction biases present in the afferents to the vi sual cortex may contribute to the orientation and direction selectivit ies found in cortical cells.