Abstract
In the primary visual cortex (V1), a neuronal response to stimulation of the classical receptive field (CRF) is suppressively modulated by the stimulus presented at the receptive field surround (SRF), depending on the relationship among the parameters of stimuli at CRF and SRF. In this study, we tested the effect of stimulus size (Exp.1) and orientation-contrast between CRF and SRF stimuli (Exp.2) in V1 neurons of anesthetized cats, and analyzed temporal properties of the surround suppression. Stationary flash of sinusoidal grating was used as stimulus. In Exp.1, neurons were stimulated by a varying diameter of circular grating patch with optimal orientation and spatial frequency for CRF. A mean CRF size of analyzed 54 neurons was 5º, and 46 neurons were suppressed by more than 25% by stimuli larger than CRF. As an increment of the outer diameter of stimulus up to 20º, the suppression became stronger and also the latency for the maximal suppression was progressively reduced. These results suggest that neurons with large receptive field and fast conduction velocity contribute to the surround suppression. In Exp.2, CRF and SRF were stimulated with the optimal grating patch and the annulus with either iso- or cross-oriented to the CRF stimulus, respectively, and stimulus onset asynchrony (SOA) was changed from -120 to +120 ms. On average, the suppression was strongest at 0 ms of SOA regardless of the orientation-contrast. However, specificity to orientation-contrast, temporal tuning to SOA and magnitude of suppression varied widely from neuron to neuron. [Jpn J Physiol 55 Suppl:S186 (2005)]
