Contralateral tactile masking between forearms

Abstract

Masking effects have been demonstrated in which tactile sensitivity is affected when one touch is close to another on the body surface. Such effects are likely a result of local lateral inhibitory circuits that sharpen the spatial tuning of a given tactile receptor. Mutually inhibitory pathways have also been demonstrated between cortical tactile maps of the two halves of the body. Occasional reports have indicated that touches on one hand or forearm can affect tactile sensitivity at contralateral locations. Here, we measure the spatial tuning and effect of posture on this contralateral masking effect. Tactile sensitivity was measured on one forearm, while vibrotactile masking stimulation was applied to the opposite arm. Results were compared to sensitivity while vibrotactile stimulation was applied to a control site on the right shoulder. Sensitivity on the forearm was reduced by over 3 dB when the arms were touching and by 0.52 dB when they were held parallel. The masking effect depended on the position of the masking stimulus. Its effectiveness fell off by 1 STD when the stimulus was 29 % of arm length from the corresponding contralateral point. This long-range inhibitory effect in the tactile system suggests a surprisingly intimate relationship between the two sides of the body.

How our body influences our perception of the world

“…This is known as long-range tactile masking (Sherrick, 1964; Braun et al, 2005; Tamè et al, 2011) and seems to indicate a precise connection between the representations of certain patches of skin. For example, the sensitivity to touch on one arm can be influenced by long-range masking only by touch on the corresponding point on the other arm (Figure 6A; D’Amour and Harris, 2014a). Likewise touches on the stomach can be affected by simultaneous touch on the corresponding part of the back (Figure 6B; D’Amour and Harris, 2014b).…”

“…By varying the position of the limbs relative to each other, we have demonstrated that long-range tactile masking also depends on the position of the limbs in space (D’Amour and Harris, 2014a). Such modulation by posture suggests that long-range tactile masking is a phenomenon at or beyond the point at which the postural body schema is derived rather than at or before the level of the primary somatosensory cortex.…”

Testing Tactile Masking between the Forearms

“…This technique provides behavioural 5,7,8,[13][14][15] evidence to support neurophysiological [16][17][18] and neuroimaging data [19][20][21][22][23] that suggest that the integration of somatosensory inputs from the two sides of the body occurs in a somatotopic representation. In these experiments, the effect of arm location was briefly examined by comparing masking when the hands were touching or parallel.…”

“…Analyses of the data was reported in 13 . Tactile sensitivity (expressed relative to the thresholds measured in the control condition) on the forearm was significantly reduced (thresholds were significantly increased) when vibrotactile masking stimulation was applied to the opposite arm (Figure 2A), demonstrating a contralateral masking effect between forearms.…”

Long-range tactile masking occurs in the postural body schema

“…Long-range tactile masking has been reported between mirror symmetric points on the hand and arm (that is, touch at a particular point on one limb has effects specifically at that same point on the other limb, Sherrick 1964;Braun et al 2005;Tamè et al 2011;D'Amour and Harris 2014a) and between the front and back of the body (D'Amour and Harris 2014b). These studies reveal unexpected connections between distantly separated parts of the body suggesting a nonlinear arrangement of the body representation.…”