Pre-stimulus beta-band oscillations influence the perception of the sound induced flash illusion

Abstract

The question whether multisensory information integration requires specific prestimulus brain states has been rarely assessed. The sound induced flash illusion is an example for the influence of auditory information on visual perception. It consists of the perception of two visual stimuli upon the presentation of only a single visual stimulus accompanied by two auditory stimuli.We used magnetoencephalography (MEG) to assess the influence of ongoing pre-stimulus oscillatory activity on varying perception of invariant stimuli. We compared cortical activity for trials in which subjects perceived two visual stimuli (i.e. an illusion) with trials in which subjects perceived only one visual stimulus (i.e. no illusion), thus keeping the stimulation fixed.Subjects perceived the illusion in ~50% of trials. In trials containing an illusion, we found stronger pre-stimulus (-.5 to -. 1 s) beta band (13-21 Hz) activity in a left temporal sensor cluster and localized it to left middle temporal gyrus (MTG). In addition to differences in local beta activity, illusory perceptions were preceded by increased alpha band (6-11 Hz) phase synchrony between lMTG and temporal, occipital and frontal cortical areas.Our results support recent reports on the influence of brain states prior to stimulation on subsequent perception, in particular a previous study by our group that audiovisual illusory perception is preceded by beta band activity in left temporal brain regions. We suggest that ongoing prestimulus fluctuations of oscillatory activity in multimodal brain regions as well as it’s varying integration into a distributed network form predispositions whether different sensory streams will be integrated or not.