Abstract
In the primary visual cortex (V1), a neuronal response to the stimulation of the classical receptive field (CRF) is suppressively modulated by the stimulus concurrently or successively presented at the receptive field surround (SRF). In the present study, we addressed whether SRF effects are spatially additive and also whether they vary according to spatial configuration of stimuli placed in SRF in V1 neurons of anesthetized cats. Stationary flashes of sinusoidal gratings were used as stimuli. The CRF stimulus was a circular grating patch with optimal size, orientation, spatial frequency and phase. For SRF stimulus, we divided SRF into eight flanks (45deg step) and presented all eight flanks (all flanks) or oppositely-faced two flanks (2-flanks) or any one flank (1-flank). Even though the predominant effect of SRF stimulation on CRF response was suppression, a fast and transient facilitation of CRF response was also occasionally observed. In ten neurons so far analyzed, when the CRF and SRF stimuli were simultaneously presented, 2-flanks SRF stimulus induced suppression with a strength comparable to that of all flanks SRF stimulus suggesting that there is a localization of suppressive field in SRF as previously reported by Walker and colleagues (1999). In some neurons, co-linear configuration of CRF and SRF gratings induced stronger suppression than other configurations, and in other neurons, parallel configuration induced stronger effect. We will also show results of changing stimulus-onset-asynchrony of stimulus presentation. [Jpn J Physiol 55 Suppl:S184 (2005)]
