Oscillatory beta activity predicts response speed during a multisensory audiovisual reaction time task: a high-density electrical mapping study

Bisensory redundant targets are processed faster than the respec-tive unisensory target stimuli alone as evidenced by substantially faster reaction times (RTs). This multisensory RT facilitation has been interpreted as an expression of integrative processing be-tween the different sensorymodalities. However, the neuronal mech-anisms underlying the RT facilitation effect are not well understood. Oscillatory responses in the beta frequency range (13--30 Hz) have been related to sensory-motor processing. Here, we investigated whether modulation of beta responses might also underlie the faster RTs seen for multisensory stimuli. Using high-density elec-trical mapping, we explored the association between early (50--170 ms) multisensory processing in the evoked beta response and RTs recorded during a simple RT task. Subjects were instructed to indicate the appearance of any stimulus in a stream of auditory-alone (A), visual-alone (V), and multisensory (AV) stimuli by a button press. Beta responses were analyzed using Morlet wavelet trans-formations. Multisensory interactions were found over frontal, occipital, central, and sensory-motor regions. Critically, beta ac-tivity correlated with mean RTs over all stimulus types. Significant negative correlations were found for frontal, occipital, and sensory-motor scalp regions. We conclude that the association between oscillatory beta activity and integrative multisensory processing is directly linked to multisensory RT facilitation effects