Suppression of premotor cortex disrupts motor coding of peripersonal space

Peripersonal space (PPS) representation depends on the activity of a fronto-parietal network including the premotor cortex (PMc) and the posterior parietal cortex (PPc). PPS representation has a direct effect on the motor system: a stimulus activating the PPS around the hand modulates the excitability of hand representation in the primary motor cortex. However, to date, direct information about the involvement of the PMc-PPc network in the motor mapping of sensory events occurring within PPS is lacking. To address this issue, we used a 'perturb-and-measure' paradigm based on the combination of transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS) techniques. Cathodal tDCS was applied to transiently suppress neural activity in PMc, PPc and primary visual cortex (V1; serving as an active control site); single-pulse TMS was used to induce motor-evoked potentials (MEPs) from hand muscles and so to measure the excitability of the hand motor representation. MEPs were compared when a sound was presented either near the hand or at a distance. In experimental sessions performed after sham-tDCS and after tDCS over the control area V1, we found a spatially dependent modulation of the hand motor representation: sounds presented near the hand induced an inhibitory motor response as compared to sounds presented far apart. Critically, this effect was selectively abolished after tDCS suppression of neural activity in PMc, but not when perturbing the activity of PPc. These findings suggest that PMc has a critical role in mapping sensory representations of space onto the motor system.