Spatially congruent visual motion modulates activity of the primary auditory cortex.

We investigated the brain responses to the transitions from the static to moving audiovisual stimuli using magnetoencephalography. The spatially congruent auditory and visual stimuli moved in the same direction whereas the incongruent stimuli moved in the opposite directions. Using dipole modeling we found that the static-to-moving transitions evoked a neural response in the primary auditory cortex bilaterally. The response started about 100 ms after the motion onset from a negative component (mvN1) and lasted during the entire interval of the stimulus motion. The mvN1 component was similar to the classical auditory N1 response to the static sound, but had smaller amplitude and later latency. The coordinates of the mvN1 and N1 dipoles in the primary auditory cortex were also similar. The amplitude of the auditory response to the moving stimuli appears to be sensitive to spatial congruency of the audiovisual motion; it was larger in the incongruent than congruent condition. This is evidence that the moving visual stimuli modulate the early sensory activity in the primary auditory cortex. Such early audiovisual integration may be specific for motion processing.