Auditory input modulates striate visual cortex activity: cortical multisensory integration begins

Abstract

Investigations have traditionally focused on activity in the sensory cortices as a function of their respective sensory inputs. However, converging evidence from multisensory research has shown that neural activity in a given sensory region can be modulated by stimulation of other sensory systems. Both electrophysiology and functional imaging support the occurrence of multisensory processing in human sensory cortex (previously described as "unisensory" cortex), based on the latency of multisensory effects and their precise anatomical localization. Still, due to inherent methodological limitations, direct evidence of the precise mechanisms by which multisensory integration occurs within human sensory cortices is lacking. Using intracranial recordings in epileptic patients (n=5) undergoing presurgical evaluation, we investigated the neurophysiological basis of multisensory integration in visual cortex. Subdural electrical brain activity was recorded while patients performed a simple detection task of randomly ordered Auditory alone (A), Visual alone (V) and Audio-Visual stimuli (AV). We then performed time-frequency analysis: first we investigated each condition separately to evaluate responses compared to baseline, then we indexed multisensory integration using both the maximum criterion model (AV vs. V) and the additive model (AV vs. A+V). Our results show that auditory input significantly modulates neuronal activity in visual cortex by resetting the phase of ongoing oscillatory activity. This appears to be a mechanism by which multisensory effects in visual cortex occur when an auditory stimulus is simultaneously presented with a visual stimulus. Here, multisensory effects are characterized by an enhancement of the multisensory response compared to the unisensory visual response. Multisensory responses were also shown to vary with respect to the additive model (that is: multisensory integration effects can be either sub- or super-additive). Our data demonstrate that auditory information commonly reaches a large portion of the striate cortex within the same time range as visual information.

Meeting abstract presented at VSS 2012