Slow-varying normalization explains diverse temporal frequency masking interactions in the macaque primary visual cortex

Neurons in the primary visual cortex (V1) respond non-linearly with increasing stimulus contrast or with presentation of multiple stimuli, which has been explained by a normalization model where the excitatory drive is divided by the summed activity of a larger neuronal population. However, while recent studies have suggested that normalization could be time and frequency-dependent, neural mechanisms underlying this dependence remain unknown. We presented two overlapping counterphasing grating stimuli (plaids), either parallelly or orthogonally, at multiple contrasts and temporal frequencies and recorded spikes, local field potential and electrocorticogram activity from V1 of bonnet macaques while they passively fixated. The resulting steady-state visually evoked potentials (SSVEPs) exhibited complicated dynamics – with “low-pass” and “band-pass” suppression profiles for orthogonal and parallel plaids, respectively. Surprisingly, adding a simple low-pass filter in the normalization signal sufficiently explained these diverse effects. Our results present a simple mechanism to explain the spectro-temporal dynamics of normalization.