Human electrocorticography shows phase resetting of visual cortical oscillatory activity by auditory stimuli

Perception is inherently multisensory, as evidenced by multisensory integration effects such as increased comprehensibility of speech when lip movements of a speaker are clearly visible in a noisy environment, as well as by audio-visual illusions such as the ventriloquism and McGurk effects. At the neural level, it has been increasingly recognized that there are cross-modal inputs even to primary sensory cortical areas that take place already at very short latencies from stimulus onset, however, understanding of the neural mechanisms by which auditory stimuli influence visual processing has been relatively limited. Given recent findings in other sense modalities, phase resetting of oscillatory visual cortex activity by auditory stimuli has emerged as a potential mechanism by which auditory stimuli might facilitate processing of visual stimuli in visual cortical areas.

In their recent study, Mercier et al. (2013) recorded brain electrical activity intracranially in patients undergoing presurgical mapping procedures. Oscillatory and evoked activity was recorded with electrodes placed in a number of occipital-visual cortical areas during presentation of auditory-only, visual-only, and audiovisual stimuli. While the authors observed also some responses in visual cortical areas evoked by auditory stimuli, the most robust effects that auditory stimuli caused in visual cortical areas was modulation / phase resetting of the ongoing oscillatory activity by auditory stimuli. Such phase resetting might be the neurophysiological-level mechanism that supports behaviorally measurable multisensory interaction effects.

Reference: Mercier MR, Foxe JJ, Fiebelkorn IC, Butler JS, Schwartz TH, Molholm S. Auditory-driven phase reset in visual cortex: human electrocorticography reveals mechanisms of early multisensory integration. Neuroimage (2013) 79:19-29. http://dx.doi.org/10.1016/j.neuroimage.2013.04.060