Neural correlates of auditory-visual stimulus onset asynchrony detection

Intersensory temporal synchrony is an ubiquitous sensory attribute that has proven to be critical for binding multisensory inputs, sometimes erroneous ly leading to dramatic perceptual illusions. However, little is known about how the brain detects temporal synchrony between multimodal sensory inputs . We used positron emission tomography to demonstrate that detecting audito ry-visual stimulus onset asynchrony activates a large-scale neural network of insular, posterior parietal, prefrontal, and cerebellar areas with the h ighest and task-specific activity localized to the right insula. Interregio nal covariance analysis further showed significant task-related functional inter-actions between the insula, the posterior thalamus, and superior coll iculus. Based on these results and the available electrophysiological and a natomical connectivity data in animals, we propose that the insula, via its known short-latency connections with the tectal system, mediates temporall y defined auditory-visual interaction at an early stage of cortical process ing permitting phenomena such as the ventriloquist and the McGurk illusions .