Task specific effect of tDCS in the healthy brain
C.M.S.Marquez, X.Zhang, A.Baens, A. Robijns, J.Rosiers, J.Vandeputte, F. Wouters, M.
Zabrzeska, N.Wenderoth
Movement Control and Neuroplasticity, K.U.Leuven, Heverlee, Belgium
Over the last decade, experimental evidence has shown that transcranial direct current stimulation
(tDCS) enhances motor skill acquisition. Anodal tDCS applied to the human primary motor cortex
(M1) has proved to have beneficial behavioral effects in motor skill learning both in healthy controls
([Reis et al. 2009;Boggio et al. 2006]) and in patients ([Boggio et al. 2008;Boggio et al. 2007]). Here
we further tested this proposal by measuring behavioral parameters of two different motor tasks:
explicit sequence learning (Experiment 1) and a visuomotor tracking task (Experiment 2). In both
experiments we applied anodal tDCS to M1 over multiple days to determine whether anodal tDCS
leads to a faster learning process, furthermore, if the effect differs on each motor task, aiming to find
what type of motor task is more sensitive to this non-invasive stimulation to make this new
therapeutic tool as efficient as possible.
Our hypothesis predicted that anodal tDCS would induce a faster learning and this improvement
would be task related. Four groups of subjects (n=32; right handed) received either anodal or sham
tDCS stimulation while trained with either a visuomotor task (pinch force task) or an explicit
sequence learning (sequence taping task) for three continuous days and performed retention test
(RT) after a week of the last training session. Experiment 1: Taping sequence task requires subjects to
tap sequences with their left hand. Their fingers are located over four buttons numbered 1-4 on a
standard PC keyboard. Sequences of number (1-4) are presented on a display while the subject taps
the corresponding finger. Subjects are required to repeat as many sequences as possible within a
given time, while maintaining a high degree of accuracy. Experiment 2: Pinch force task requires
subjects to pinch their left thumb and index finger in order to move a cursor inside a target zone, as
fast and accurately as possible. The targets appear in a fixed sequence with cursor displacement
proportionate to pinch force. All subjects followed the same protocol except for the motor task used;
all subjects began with a pretest to record baseline of the performance. Motor task training
consisted of 20 min training and 20min resting for 3 continuous days. Retention tests were
performed on the final day of training and one week later. tDCS was applied for 20 min over M1
during the motor task training. Subjects received either anodal tDCS or sham tDCS.
In both experiments, participants performed better in their retention tests compare to the pretest.
Motor training with anodal tDCS showed a significant learning improvement compare to the sham
tDCS group in both experiments. Also, Sham groups in both experiments increased to a non
significant level. Interestingly, these findings were less significant during the sequence task indicated
by a difference in learning gain for the anodal groups between experiments.
Our results suggest that anodal tDCS apply over M1 has a positive influence on motor task learning,
nevertheless, the type of the motor task per se also plays a very important role to noninvasive
cortical stimulation, implying a task specific effect of tDCS.
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