Electrophysiological evidence for the effect of tool use on visuo-tactile integration in near and far space

The representation of the body and the multisensory space near it is modulated by the active use of long tools as suggested by behavioural evidence in humans. This might suggest that the tools become part of the body representation, extending near space into far space. However, little is known about the underlying neural mechanisms and recent studies have suggested that tool-mediated effects on visuo-tactile integration in far space are simply due to the salient tip of the tool which attracts visual attention in far space. Here, we investigate whether the electrophysiological correlates of visuo-tactile integration in near and far space are modulated by active tool use in healthy humans. ERPs elicited by visuo-tactile stimuli in near and far space were measured after short and long tool use. ERPs recorded close to the somatosensory cortex in the P100 time-range were enhanced after long as compared to short tool use. No such modulation was observed over occipital areas where effects of visual attention would be expected, ruling out a role of visual attention in these effect. This pattern of results provides the first electrophysiological evidence that the active use of long tools increased neural activity within somatosensory areas of the brain, in line with the idea of plastic changes to the representation of the body induced by the use of tools.