Multisensory Parietal Cortex contributes to Visual Enhancement of Touch in Humans: A Single-Pulse TMS Study

We used transcranial magnetic stimulation (TMS) to investigate how the visual context provided by viewing ones own body influences somatosensory processing. In the visual enhancement of touch (VET) effect, viewing the body enhances tactile acuity relative to viewing a nonbody object. Single-pulse TMS was delivered over anterior intraparietal sulcus (aIPS), which is crucial for integrating visual and somatosensory information related to the body, during the interval between a brief glimpse of the arm, or an object, and tactile stimulation. TMS to aIPS just after visual stimulation abolished VET, while TMS at the time of touch itself did not. Disrupting nearby areas just anterior or posterior to aIPS left the VET effect intact. Viewing the arm may activate multisensory areas in aIPS, which may then rapidly modulate somatosensory circuits. We suggest that this enhancement of touch by vision involves feedback signals from aIPS to unimodal somatosensory cortex. Our study provides causal evidence of a specific multisensory mechanism that modulates tactile processing in the human brain.