Vision and gaze direction modulate tactile processing in somatosensory cortex: evidence from event-related brain potentials.

Several behavioural studies have shown that directing one's gaze at a body part reduces detection speed and enhances discrimination of tactile stimuli at that location. We investigated how vision of a body part stimulated and manipulations of gaze direction affect tactile processing. Participants' gaze was directed to one of their hands, with vision of this hand either available or prevented in different experiments. They had to detect infrequent tactile targets among non-targets. Somatosensory event-related brain potentials were recorded in response to stimulation of the hand towards which gaze was directed (G+ trials) and in response to stimulation of the other hand (G- trials). When vision (V+) of the hand gaze was directed at was available (G+V+), an early positivity overlapping with the P45 and N 80 component was observed for G+V+ trials relative to G-V- trials. In contrast, when the hands were occluded from view (V-), an enhanced N 140 component followed by a late negativity was observed for G+V- as compared to G-V- trials. It is suggested that vision of the body part stimulated can modulate processing in primary somatosensory cortex (S1), while effects of gaze direction in the absence of vision of the body part touched are located in higher order somatosensory areas. Such effects of vision and gaze on tactile processing may be mediated by pathways from multimodal brain regions to somatosensory cortex.