Conventional vs. High-definition tDCS: A Comparison of Neurophysiological and Behavioural Effects

Abstract

High-definition transcranial direct current stimulation (HD-tDCS) seems to overcome a drawback of Conventional tDCS: the wide-spread diffusion of the electric field. Nevertheless, most of the differences that characterise the two techniques are based on mathematical simulations and not on real, behavioural and neurophysiological, data. The study aims to compare Conventional and HD-tDCS, investigating differences both at a behavioural level, in terms of dexterity performance, and a neurophysiological level, as modifications of alpha and beta power as measured with EEG. Thirty participants took part in three sessions, one for each montage: Conventional tDCS, HD-tDCS, and sham. In all the conditions, the anode was placed over C4, while the cathode/s placed according to the montage. At baseline, during, and after each stimulation condition, dexterity was assessed with a Finger Tapping Task. In addition, resting-state EEG was recorded at baseline and after the stimulation. Power spectrum density was calculated, selecting two frequency bands: alpha (8–12 Hz) and beta (18–22 Hz). Linear mixed effect models (LMMs) were used to analyse the modulation induced by tDCS. To evaluate differences among the montages and consider state-dependency phenomenon, the post-stimulation measurements were covariate-adjusted for baseline levels. We observed that HD-tDCS induced an alpha power reduction in participants with lower alpha. Conversely, Conventional tDCS induced a beta power reduction in participants with higher beta at baseline. Furthermore, data suggested a positive behavioural effect of HD-tDCS on dexterity in participants with lower beta at baseline. Conventional and HD-tDCS distinctively modulated cortical activity. The study highlights the importance of considering state-dependency to determine the effects of tDCS on individuals.

Multichannel Transcranial Direct Current Stimulation Combined With Treadmill Gait Training in Patients With Parkinson's Disease: A Pilot Study

“…Conventional tDCS produces a wide-spread electric field with low spatial specificity, reaching target areas of the brain with low density. To increase the density and focality of current to the target area, multi-tDCS montages with multiple configurations were used in this study ( 7 ). The most used multi-tDCS montage is the 4 × 1 ring configuration, which consists of one active electrode placed on the area of interest and four reference electrodes surrounding it.…”