P 6. tDCS-induced effects on paired-pulse inhibition in the primary somatosensory cortex

Abstract

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique used to modulate cortical excitability. In the motor domain, there is consensus that anodal tDCS increases cortical excitability, whereas cathodal tDCS decreases it. On the other hand, inconsistent results of tDCS-induced effects in the sensory domain have been reported. The aim of the present study was to investigate (A) changes in cortical excitability within primary somatosensory cortex (S1) by means of single-pulse somatosensory evoked potentials (SEPs) and (B) intracortical inhibition by means of paired-pulse SEPs when tDCS was applied over left SM1. 10 min of anodal, cathodal or sham tDCS was applied over the left SM1 using saline-soaked sponge electrodes (35 cm 2 electrodes, 1 mA, current density 0.028 mA/cm 2 ). Before, immediately after as well as 10 min after termination of tDCS, single-and paired-pulse SEP recordings were performed. We hypothesized that tDCS will induce polarity specific changes in cortical excitability within left S1. Furthermore, we reasoned that anodal tDCS will reduce paired-pulse inhibition within left S1 while cathodal tDCS will result in an augmentation of inhibition relative to sham stimulation. 10 min of anodal and cathodal tDCS over SM1 did not result in any significant excitability changes within left S1. However, anodal tDCS resulted in a reduction of paired-pulse inhibition within left S1 10 min after termination of stimulation. No change in paired-pulse inhibition could be observed after cathodal tDCS. Here we provide novel evidence that anodal tDCS affects inhibitory processing within S1, a finding that might improve our understanding about the underlying neural mechanisms of tDCS on somatosensory processing.