Short and long duration transcranial direct current stimulation (tDCS) over the human hand motor area

Abstract

The aim of the present paper is to study effects of short and long duration transcranial direct current stimulation (tDCS) on the human motor cortex. In eight normal volunteers, motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) were recorded from the right first dorsal interosseous muscle, and tDCS was given with electrodes over the left primary motor cortex (M1) and the contralateral orbit. We performed two experiments: one for short duration tDCS (100 ms, 1, 3 or 5 mA) and the other for long duration tDCS (10 min, 1 mA). The stimulus onset asynchrony (SOA) between the onset of tDCS and TMS were 1-7 and 10-120 ms for the former experiment. In the latter experiment, TMS was given 0-20 min after the end of 10 min tDCS. We evaluated the effect of tDCS on the motor cortex by comparing MEPs conditioned by tDCS with control MEPs. Cathodal short duration tDCS significantly reduced the size of responses to motor cortical stimulation at SOAs of 1-7 ms when the intensity was equal to or greater than 3 mA. Anodal short duration tDCS significantly increased MEPs when the intensity was 3 mA, but the enhancement did not occur when using 5 mA conditioning stimulus. Moreover, both anodal and cathodal short duration tDCS decreased responses to TMS significantly at SOAs of 20-50 ms and enhanced them at an SOA of 90 ms. Long duration cathodal tDCS decreased MEPs at 0 and 5 min after the offset of tDCS and anodal long duration tDCS increased them at 1 and 15 min. We conclude that the effect at SOAs less than 10 ms is mainly caused by acute changes in resting membrane potential induced by tDCS. The effect at SOAs of 20-100 ms is considered to be a nonspecific effect of a startle-like response produced by activation of skin sensation at the scalp. The effect provoked by long duration tDCS may be short-term potentiation or depression like effects.

Impact of tDCS on performance and learning of target detection: Interaction with stimulus characteristics and experimental design

“…Because tDCS causes sensation at the site of the electrodes (Furubayashi et al, 2008;Gandiga, Hummel, & Cohen, 2006;Poreisz et al, 2007), we also examined the relationship between expectancy and behavioral effects through the examination of the relationship between skin sensation produced by tDCS and behavioral performance. This analysis tested the hypothesis that participants that experienced stronger somatic stimulation from tDCS would also expect to have larger behavioral effects, thus possibly influencing the test results.…”

Parietal Contributions to Visual Working Memory Depend on Task Difficulty

“…During cathodal and anodal stimulation 1.5 mA current was applied for 10 min. Previous studies have found an effect of tDCS with 10 min of stimulation (Furubayashi et al, 2008;Berryhill et al, 2010;Andrews et al, 2011;Mulquiney et al, 2011;Antal et al, 2012;Berryhill and Jones, 2012;Kasashima et al, 2012). During sham stimulation participants received stimulation in which current lasted for 20 s at the start and end of the 10 min but no stimulation occurred in between.…”

Bilateral Transcranial Direct Current Stimulation Modulates Activation-Induced Regional Blood Flow Changes during Voluntary Movement

“…In the current protocol, we used a current density of 0.08 mA/cm 2 which is larger than what has been used in most tDCS studies (B0.02 mA/cm 2 ). Only two other studies have safely used stronger current intensities (0.141 mA/cm 2 ) but with shorter stimulation duration (Furubayashi et al, 2008;Kwon et al, 2008). Using these higher intensities, Kwon et al were unable to show a convincing effect of tDCS.…”