Tactile temporal processing in the auditory cortex.

Perception of the outside world results from integration of information simultaneously derived via multiple senses. Increasing evidence suggests that the neural underpinnings of multisensory integration extend into the early stages of sensory processing. In the present study, we investigated whether the superior temporal gyrus (STG), an auditory modality-specific area, is critical for processing tactile events. Transcranial magnetic stimulation (TMS) was applied over the left STG and the left primary somatosensory cortex (SI) at different time intervals (60, 120, and 180 msec) during a tactile temporal discrimination task (Experiment 1) and a tactile spatial discrimination task (Experiment 2). Tactile temporal processing was disrupted when TMS was applied to SI at 60 msec after tactile presentation, confirming the modality specificity of this region. Crucially, TMS over STG also affected tactile temporal processing but at 180 msec delay. In both cases, the impairment was limited to the contralateral touches and was due to reduced perceptual sensitivity. In contrary, tactile spatial processing was impaired only by TMS over SI at 60-120 msec. These findings demonstrate the causal involvement of auditory areas in processing the duration of somatosensory events, suggesting that STG might play a supramodal role in temporal perception. Furthermore, the involvement of auditory cortex in somatosensory processing supports the view that multisensory integration occurs at an early stage of cortical processing.