Individual differences in TMS sensitivity influence the efficacy of tDCS in facilitating sensorimotor adaptation

• Published in: Brain stimulation Vol. 12; no. 4; pp. 992 - 1000
• Main Authors: Labruna, L., Stark-Inbar, A., Breska, A., Dabit, M., Vanderschelden, B., Nitsche, M.A., Ivry, R.B.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2019
• Subjects: Adaptation, Physiological - physiology; Adult; Cognition - physiology; Female; Humans; Individual differences; Individuality; Learning - physiology; Male; Motor Cortex - physiology; Psychomotor Performance - physiology; Rest - physiology; rMT; Sensorimotor Cortex - physiology; Sensorimotor learning; tDCS; TMS; Transcranial Direct Current Stimulation - methods; Transcranial Magnetic Stimulation - methods; Sensorimotor learning; rMT; TMS; tDCS; Individual differences
• ISSN: 1935-861X; 1876-4754; 1876-4754
• DOI: 10.1016/j.brs.2019.03.008

Transcranial direct current stimulation (tDCS) can enhance cognitive function in healthy individuals, with promising applications as a therapeutic intervention. Despite this potential, variability in the efficacy of tDCS has been a considerable concern. /Hypothesis: Given that tDCS is always applied at a set intensity, we examined whether individual differences in sensitivity to brain stimulation might be one variable that modulates the efficacy of tDCS in a motor learning task. In the first part of the experiment, single-pulse transcranial magnetic stimulation (TMS) over primary motor cortex (M1) was used to determine each participant's resting motor threshold (rMT). This measure was used as a proxy of individual sensitivity to brain stimulation. In an experimental group of 28 participants, 2 mA tDCS was then applied during a motor learning task with the anodal electrode positioned over left M1. Another 14 participants received sham stimulation. M1-Anodal tDCS facilitated learning relative to participants who received sham stimulation. Of primary interest was a within-group analysis of the experimental group, showing that the rate of learning was positively correlated with rMT: Participants who were more sensitive to brain stimulation as operationalized by our TMS proxy (low rMT), showed faster adaptation. Methodologically, the results indicate that TMS sensitivity can predict tDCS efficacy in a behavioral task, providing insight into one source of variability that may contribute to replication problems with tDCS. Theoretically, the results provide further evidence of a role of sensorimotor cortex in adaptation, with the boost from tDCS observed during acquisition. •Study examines individual differences in tDCS efficacy, using motor learning task.•TMS threshold used as a proxy of variation in sensitivity to brain stimulation.•tDCS, with anode over M1, was applied during sensorimotor adaptation task.•rMT was positively correlated with efficacy of tDCS in accelerating learning.•Study identifies one source of between-subject variability in efficacy of tDCS.