P182 Effects of transcranial direct current stimulation (tDCS) on cognitive activity

Abstract

Transcranial direct current stimulation (tDCS) is known to modulate neuronal network activity thus affecting cognitive performance. tDCS has demonstrated prolonged effects, reflecting plastic processes in the brain (Nitsche and Paulus, 2001). We investigated an influence of tDCS on EEG waves, cognitive performance and activation of regulation mechanisms in autonomic nervous system. Eight healthy male volunteers underwent anodal/cathodal and sham stimulation on separate days in a single blind crossover trial. tDCS was applied for 10 min at 1.5 mA current with an active electrode over T3 area and a passive electrode over A2 lead. EEG and heart rate variability were recorded during a two-minute interval of eyes-closed/eyes-opened background state before and after stimulation, during a cognitive load (a letter cancelation and an arithmetic test) and during a background state at the end of the experiment. Before the experiment volunteers have passed tapping test to assess Pavlovian nervous system properties. We found that an anodal stimulation provoked an increase in cognitive performance in 87% cases, while the cathodal one showed a slight decrease in 38% cases; other probes demonstrated an opposite effect. We found subject-depended changes in frequency band power after tDCS. Generally, anodal stimulation increased power of all bands, while cathodal one had an opposite effect (Fig. 1). The maximum effects were observed at T3/T4, F3 and O2 leads. We found correlations between the balance of the strength of excitation and inhibition in the nervous system and the changes of theta and beta power after cathodal stimulation. We observed an increase in beta activity across well-balanced individuals while solving cognitive tasks after the cathodal stimulation. Consequently, tDCS affects cognitive and regulatory activity of the brain. Effects depend on the polarity of the active electrode. Anodal stimulation mostly increases cortical electrical activity in temporal and left prefrontal areas. The effect entails an increase in cognitive performance and a reorganization in control of autonomic nervous system which is responsible for activation of behavioral physiological resources. Effects of cathodal stimulation depend on individual balance of the strength of excitation and inhibition in the brain. Download : Download high-res image (122KB) Download : Download full-size image