Seeing touch in the somatosensory cortex: A TMS study of the visual perception of touch

Abstract

Recent studies suggest the existence of a visuo-tactile mirror system, comprising the primary (SI) and secondary (SII) somatosensory cortices, which matches observed touch with felt touch. Here, repetitive transcranial magnetic stimulation (rTMS) was used to determine whether SI or SII play a functional role in the visual processing of tactile events. Healthy participants performed a visual discrimination task with tactile stimuli (a finger touching a hand) and a control task (a finger moving without touching). During both tasks, rTMS was applied over either SI or SII, and to the occipital cortex. rTMS over SI selectively reduced subject performance for interpreting whether a contralateral visual tactile stimulus contains a tactile event, whereas SII stimulation impaired visual processing regardless of the tactile component. These findings provide evidence for a multimodal sensory-motor system with mirror properties, where somatic and visual properties of action converge. SI, a cortical area traditionally viewed as modality-specific, is selectively implicated in the visual processing of touch. These results are in line with the existence of a sensory mirror system mediating the embodied simulation concept. Hum Brain Mapp 32:2104-2114,

Dissecting neural circuits for multisensory integration and crossmodal processing

“…Notably, the time course of TMS-induced perturbations differs between the two targets: TMS targeting OFA at 60 ms after stimulus onset maximally disrupts performance while the largest effects of S1-TMS occur with pulses delivered 130 ms after visual stimulus onset [63]. Visual processing related to non-face body parts also recruits somatosensory cortex, as online rTMS targeting S1 impairs discrimination performance in a task requiring participants to judge whether a video depicts a hand being touched [65]. Thus, somatosensory cortex may be specialized for processing body-related information across sensory modalities.…”

Synchronization to auditory and visual rhythms in hearing and deaf individuals

“…Kowalska and Szelag (2006) found that congenitally deaf adolescents were less able to estimate temporal duration, and Bolognini et al (2011) found that deaf adults were impaired compared to hearing adults in discriminating the temporal duration of touches. Bolognini et al (2011) also provided TMS evidence that auditory association cortex was involved in temporal processing at an earlier stage for deaf participants, which correlated with their tactile temporal impairment. Finally, several studies have documented temporal sequencing deficits in deaf children (e.g.…”

Effect of tactile stimulation on primary motor cortex excitability during action observation combined with motor imagery

“…Studies suggest that a higher brain system is involved in motor imagery and that sensory information could affect M1 excitability during action observation. In fact, it has been reported that a mirror neuron system that performs the cross-modal processing required to integrate visual and tactile information exists in the somatosensory area [17].…”