It has been claimed that oscillatory firing activity plays a functional role in neural systems. Evidence suggests that rhythmic activity in the alpha range (~10Hz) has a causal effect in visual perception and attention deployment (Romei et al., 2008). The present study addresses the causal role of brain rhythms in tactile processing. We used rhythmic TMS to entrain specific frequencies (10 and 20Hz) focusing on the parietal lobe (IPS) and primary somatosensory areas (S1). The results revealed that entrainment of alpha frequency in the IPS decreases contralateral somatosensory detection and enhances ipsilateral performance [experiment 1]. Interestingly, we found that this TMS-induced ipsilateral enhancement effect abides with an external frame of reference, not to the anatomical side [experiment 2]. Furthermore, the effect of pre-stimulus entrainment of 10 and 20Hz activity in S1 is not univocal when arrhythmic TMS is engaged [experiment 3]. Altogether, the present findings suggest that the functional role in tactile processing of alpha frequency in IPS is specific to the interaction with the external world, indicating similarities between senses (vision and touch) in the communication between top-down (parietal) and primary sensory areas (V1 or S1). Pre-stimulus S1 rTMS might affect performance regardless of the frequency engaged, that is, when the stimulus is absent (pre-stimulus) TMS decreases cortical excitability in S1.

Tactile processing; rhythmic TMS; Intra-Parietal sulcus; Primary Somatosensory Cortex