ORIENTATION SELECTIVITY OF THALAMIC INPUT TO SIMPLE CELLS OF CAT VISUAL-CORTEX

MORE than 30 years after Hubel and Wiesel(1) first described orientati on selectivity in the mammalian visual cortex, the mechanism that give s rise to this property is still controversial. Hubel and Wiesel(1) pr oposed a simple model for the origin of orientation tuning, in which t he circularly symmetrical receptive fields of neurons in the lateral g eniculate nucleus that excite a cortical simple cell are arranged in r ows. Since this model was proposed, several experiments(2-6) and neuro nal simulations(7,8) have suggested that the connectivity between the lateral geniculate nucleus and the cortex is not well organized in an orientation-specific fashion, and that orientation tuning arises inste ad from extensive interactions within the cortex. To test these models we have recorded visually evoked synaptic potentials in simple cells while cooling the cortex(9), which largely inactivates the cortical ne twork, but leaves geniculate synaptic input functional. We report that the orientation tuning of these potentials is almost unaffected by co oling the cortex, in agreement with Hubel and Wiesel's original propos al(1).