Vision of the Body Modulates Somatosensory Intracortical Inhibition

Abstract

The magnitude of somatosensory evoked potentials (SEPs) elicited by simultaneous electrical stimulation of adjacent digits is generally less than the sum of potentials evoked by stimulation of each digit individually. This under-additivity suggests suppression between representations of adjacent skin regions and may reflect a process of lateral inhibition by interneurons in somatosensory cortex. Given that simply viewing the body enhances tactile acuity and that tactile acuity depends on cortical lateral inhibition, we investigated how viewing the body modulates suppressive interactions between simultaneous afferent volleys from adjacent fingers. We recorded SEPs evoked by electrical stimulation of the right index and middle fingers, either individually or simultaneously, while participants viewed either their own hand or an object. In between trains of electrical stimuli, participants discriminated the orientation of tactile gratings applied to either finger. Consistent with previous findings, viewing the hand enhanced tactile acuity. Furthermore, viewing the hand increased the suppression of the P50 potential due to simultaneous electrical stimulation of both fingers. Moreover, the visual enhancement of tactile performance correlated across participants with the visual modulation of suppression. These results demonstrate that vision enhances somatosensation by modulating activity of inhibitory interneuronal circuits in the somatosensory cortex.

Congruency of body-related information induces somatosensory reorganization

“…Considering both previous evidence (Cardini et al, 2013(Cardini et al, , 2011Longo et al, 2009) and the present findings, we speculate that promoting stable representation of the body -by delivering coherent body-related inputs -might consequently induce sharpening in somatosensory maps, potentially improving tactile sensitivity and reducing pain. Conversely, distorted bodily representation, evoked by co-occurrence of discrepant signals, could be responsible for somatosensory blurring, eventually affecting tactile discrimination ability and causing or exacerbating pain.…”

“…Further, we recently showed that vision of the stimulated hand, compared to vision of a non-body object, increases somatosensory suppression, as well as enhancing tactile sensitivity on the observed location (Cardini et al, 2011).…”

“…Previous studies suggested that integration of congruent body-related visual, tactile, and proprioceptive inputs promotes this coherence, eventually enhancing somatosensation (Cardini et al, 2011;. Modulation of the strength of lateral inhibition in somatosensory cortex is thought to be the key mechanism responsible for these changes.…”

“…ERP components of interest were selected on the basis of visual inspection and on the basis of previous studies on tactile processing (Cardini et al, 2012(Cardini et al, , 2011Gandevia et al, 1983;Gillmeister and Forster, 2012) …”

“…Flexibility of lateral inhibition has been recently hypothesised to underlie the widespread effects of vision of the body on somatosensory processing, for example on touch (Cardini et al, 2011;Haggard et al, 2007) and pain (Haggard et al, 2007;Longo et al, 2009). The results of Cardini and colleagues (2011) provided evidence supporting this interpretation (see Haggard et al, 2013 for review).…”