Gamma Oscillation Evoked By Surround Suppression In Mouse Primary Visual Cortex

In mammalian primary visual cortex,stimulus in non-classical receptive field(nCRF)of visual neuron can modulate spiking activity caused by stimulus in the classical receptive field(CRF).If stimulus in nCRF reduces the spiking activity caused by stimulus in CRF,it is called surround suppression.Amount of researches has provided that surround suppression is the basis for identifying the bending,bulging,integrating or separating visual information.The mechanism of surround suppression is very complex,which is related to the horizontal connection at primary visual cortex and also related to the feedback modulation from advanced visual cortex.In recent years,researchers have made great progress by electrophysiology studies on spiking activity influenced by surround suppression on mammals such as cats,monkeys,and mice.However,less is known about the local field potential(LFP)properties and the relationship between the LFP and the spiking activity of surround suppression process.In this study,anesthetized mice were used to record the spiking activity and LFP of the visual neurons to primary visual cortex using single-unit electrophysiological recording when stimulated by to various stimulus parameters which cause different degrees of surround suppression.We studied the LFP characteristics,especially in gamma frequency band,under different degrees of surround suppression and its relationship with the spiking activity characteristics and the stimulus parameters,we want to explore the mechanism of action of nCRF and gamma oscillation on the surround suppression.We found that:(1)the neurons at the primary visual cortex of mice can be classified into inhibitory cells,facilitatory cells,and disinhibitory cells according to the spatial summation characteristics.(2)The gamma power peak in LFP is consistent with the trend of the spatial summation curve of the spiking activity.(3)When we cover the receptive filed area with a grey mean luminance circle,the gamma power peak shows a decreasing trend with the increasing circle size.(4)Under either small area stimulus,which covers CRF,or large area stimulus,which covers CRF and nCRF,the gamma power peak in LFP increases when stimulus contrast increases,where the gamma power peak induced by large-area stimulus is higher.(5)For different stimulus orientation,the large area stimulus evokes higher gamma power peak than the small area stimulus.And in high gamma band,the large area stimulus shows better orientation selectivity.Former studies deemed that the formulation of gamma oscillation is related to inhibitory inter neurons,i.e.the neural circuit with interneurons causes the gamma oscillation at the primary visual cortex.Our study further proved that the gamma oscillation in CRF and nCRF plays an important role in the modulation of the surround suppression process.