Temporal properties of spatial frequency tuning of surround suppression in the primary visual cortex and the lateral geniculate nucleus of the cat.

In primary visual cortex (V1) neurons, a stimulus placed in the extraclassical receptive field suppresses the response to a stimulus within the classical receptive field (CRF), a phenomenon referred to as surround suppression. The aim of the present study was to elucidate the mechanisms of surround suppression in V1. Using stationary-flashed sinusoidal grating as stimuli, we observed temporal changes of surround suppression in V1 and the lateral geniculate nucleus (LGN) and of the response to CRF stimulation in V1. The spatial frequency (SF) tuning of surround suppression in V1 neurons changed over time after the stimulus onset. In the early phase (< 50 ms), the SF tuning was low-pass, but later became band-pass that tuned to the optimal SF in response to CRF stimulation. On the other hand, the SF tuning of CRF responses in V1 was band-pass throughout the response time whereas the SF peak shifted slightly toward high SF. Thus, SF tuning properties of the CRF response dissociated from that of surround suppression in V1 only in the early phase. We also confirmed that the temporal changes of the SF tuning of surround suppression in the LGN occurred in the same direction as surround suppression in V1, but the shift from low-pass to band-pass SF tuning started later than that in V1. From these results, we suggest that subcortical mechanisms contribute to early surround suppression in V1, whereas cortical mechanisms contribute to late surround suppression.