Electrophysiological correlates of tactile remapping.

Orienting our gaze or attention to the location of tactile events in the skin feels natural and effortless. However, this process requires combining somatosensory and proprioceptive information in a non-trivial, time consuming, fashion. Here we address the time course of tactile remapping, from somatotopically-based representations, to a spatiotopic reference frame. We compared electrical responses at the scalp evoked by touch at one finger as participants held their arms straight or else, crossed about the body midline. This postural manipulation creates a conflict between frames of reference, which can be used to reveal the consequences of spatial remapping. Behavioural performance was gauged online for crossed and uncrossed postures using bimanual temporal order judgment (TOJ) trials occurring occasionally during the recording session. The first electrophysiological signs of tactile remapping were observed around 70 ms after the tactile event, overlapping in time with the somatosensory component N80. This electrophysiological effect was strongly lateralized to the left scalp and independent of the hand being stimulated. Moreover, participants who manifested a stronger behavioural conflict between frames of reference in the TOJ task displayed a larger electrophysiological effect. Based on these findings, and the known properties of the somatosensory network, we argue that remapping of tactile space depends on fast feedback projections from association areas of the parietal cortex, and encompasses a left-lateralized fronto-parietal network supporting the selection of guided actions.