Multisensory spatial interactions: a window onto functional integration in the human brain.

Incoming signals from different sensory modalities are initially processed in separate brain regions. But because these different signals can arise from common events or objects in the external world, integration between them can be useful. Such integration is subject to spatial and temporal constraints, presumably because a common source is more likely for information arising from around the same place and time. This review focuses on recent neuroimaging data concerning spatial aspects of multisensory integration in the human brain. These findings indicate not only that multisensory integration involves anatomical convergence from sensory-specific ('unimodal') cortices into multisensory ('heteromodal') brain areas, but also that multisensory spatial interactions can affect even so-called 'unimodal' brain regions. Such findings call for a revision of traditional assumptions about multisensory processing in the brain.