Functional Connectivity Is Stronger Between Unisensory and Multisensory Regions for Nonsimultaneous Judgments of Visual-Tactile Stimuli.

Multisensory integration is an automatic process that occurs across unisensory and multisensory areas of the brain. Although multisensory integration is often quantified using the simultaneity judgment task, which measures the temporal binding window for multisensory integration, little is known about the neural processes associated with the task. In 26 participants, we used electroencephalography to measure functional connectivity between parietal-occipital, parietal-central, and central-occipital regions during the simultaneity judgment task. Our aim was to compare connectivity patterns associated with simultaneous and nonsimultaneous perception, which is important for calculating the temporal binding window. Our results show that functional connectivity in the beta frequency was stronger between parietal-occipital, parietal-central, and central-occipital regions when individuals perceived visual-tactile stimuli as nonsimultaneous than simultaneous. However, connectivity was only stronger in the theta and alpha frequencies for parietal-central and central-occipital regions. Stronger connectivity in the theta and alpha frequencies is likely associated with detecting and encoding changes in temporal dynamics between cross-modal stimuli, and in the beta frequency, stronger connectivity is likely related to a violation of expectancy for simultaneous stimuli. Overall, our findings demonstrate that functional connectivity between unisensory and multisensory neural regions occurring during and immediately following stimulus presentation is important for the perception of simultaneity.