Abstract
Brain states prior to the presentations of physical stimuli shape the processing of the sensory input. It has been demonstrated that the amplitude and the phase of prestimulus alpha-band oscillation (7 -13 Hz), which are thought to have an inhibitory function, influence subsequent perceptual performance. Recently, prestimulus alpha power has been found to be negatively correlated with the amplitude of the C1 component of visual event-related potentials (ERP), which is thought to arise from afferent input onto the primary visual cortex. However, it remains unknown how the phase of prestimulus alpha is related to the C1 component. In current study, we reanalyzed the EEG dataset collected by Iemi et al. (2019) to investigate this question. In their experiment, participants (N = 25) were presented with a pair of task-irrelevant, high-contrast checkerboard wedges either in the upper (UVF) or lower (LVF) visual field with equal probability. These stimuli produced large amplitude C1 components which showed the typical polarity reversal with visual field location, suggestive of a calcarine source. We computed global field power (GFP) during the C1 time window, which is independent of the reference electrode. The trials were sorted based on the single-trial estimates of phase of prestimulus alpha and then the GFP amplitudes between phase levels were compared. Our results showed that, in both UVF and LVF, the GFP amplitude decreases with the phases deviating from the preferred phase angle at which GFP amplitudes were largest. Single-trial circular-linear associations between prestimulus phase and poststimulus GFP revealed significant effects restricted to the alpha frequency. These findings demonstrate that the phase of prestimulus alpha oscillations could modulate early stages of visual processing by gating the feedforward flow of sensory input between the thalamus and V1.