Causal role of the individual alpha phase in multisensory perception

The phase of alpha oscillations is proposed to reflect perceptual cycles. Yet, human EEG/MEG studies have yielded inconsistent results, perhaps because they used correlative approaches that did not consider causal phase-perception relationships. In a multi-day computational EEG study, we developed the neurobehavioral link function (NBLF) as a new approach to model individual sinusoidal relationships between the alpha phase and multisensory perception and to test for causality. Rhythmic 10 Hz visual stimulation entrained the alpha phase at 0{degrees} or 180{degrees} relative to audiovisual target onset. Entrainment effects on multisensory integration only emerged when individual NBLFs, which were related to alpha phase coupling between early audio-visual cortices, were included in the analysis. A follow-up psychophysical experiment confirmed individual phase-dependent effects at 5 and 10 Hz, but not 15 Hz. Our results suggest that the individual alpha phase causally modulates perceptual cycles in multisensory integration and advocate for personalized, phase-targeting strategies in neurotechnologies.