FUNCTION OF GABA(A) INHIBITION IN SPECIFYING SPATIAL-FREQUENCY AND ORIENTATION SELECTIVITIES IN CAT STRIATE CORTEX

Responses of simple and complex cells in cat striate cortex were studi ed with moving sine-wave gratings before and during application of the GABA(A) receptor antagonist bicuculline methiodide. Both simple and c omplex cells exhibited a broadening of their spatial frequency tuning functions under bicuculline. This was especially evident at spatial fr equencies lower than the ones the cell was responding to before the dr ug administration. The effects cannot be explained by response saturat ion and could be reversed by cessation of the iontophoresis. The resul ts indicate that the band-pass response characteristics of the spatial frequency response functions of striate cells derive largely from int racortical inhibition. The findings have implications also for the ori entation selectivity of cortical cells. Since many geniculate cells ar e tuned for stimulus orientation at higher spatial frequencies, suppre ssion of the low-spatial-frequency component would remove some of the orientation non-specific response in striate cortical cells and contri bute to their orientation selectivity.