Transcranial Direct-Current Stimulation Does Not Affect Implicit Sensorimotor Adaptation: A Randomized Sham-Controlled Trial

Abstract

Humans constantly calibrate their sensorimotor system to accommodate environmental changes, and this perception-action integration is extensively studied using sensorimotor adaptation paradigms. The cerebellum is one of the key brain regions for sensorimotor adaptation, but previous attempts to modulate sensorimotor adaptation with cerebellar transcranial direct current stimulation (ctDCS) produced inconsistent findings. Since both conscious/explicit learning and procedural/implicit learning are involved in adaptation, researchers have proposed that ctDCS only affects sensorimotor adaptation when implicit learning dominates the overall adaptation. However, previous research had both types of learning co-exist in their experiments without controlling their potential interaction under the influence of ctDCS. Here, we used error clamp perturbation and gradual perturbation, two effective techniques to elicit implicit learning only, to test the ctDCS effect on sensorimotor adaptation. We administrated ctDCS to independent groups of participants while they implicitly adapted to visual errors. In Experiment 1, we found that cerebellar anodal tDCS had no effect on implicit adaptation induced by error clamp. In Experiment 2, we applied both anodal and cathodal stimulation and used a smaller error clamp to prevent a potential ceiling effect, and replicated the null effect. In Experiment 3, we used gradually imposed visual errors to elicit implicit adaptation but still found no effect of anodal tDCS. With a total of 174 participants, we conclude that the previous inconsistent tDCS effect on sensorimotor adaptation cannot be explained by the relative contribution of implicit learning. Given that the cerebellum is simultaneously involved in explicit and implicit learning, our results suggest that the complex interplay between the two learning processes and large individual differences associated with this interplay might contribute to the inconsistent findings from previous studies on ctDCS and sensorimotor adaptation.

Neurophysiology of cerebellar ataxias and gait disorders

“…However, other studies attempting to replicate the beneficial effect of cerebellar TDCS on visuomotor adaptation were unsuccessful ( Panouillères et al, 2015 , Wang et al, 2022 ). For instance, one study examined 192 subjects in seven different visuomotor adaptation experiments with varying task parameters and stimulation timing and found no significant differences to sham (Placebo) stimulation ( Jalali et al, 2017 , Hulst et al, 2017 ).…”

Sensorimotor adaptation in spatial orientation task: a fNIRS study

“…During continuous sensorimotor conflict, the sensorimotor system aims to compensate for the perturbations, reduce error, and return to its former performance level. This process is referred to as sensorimotor adaptation, and involves two mechanisms 2 . One is explicit adaptation, which employs a cognition-based motor strategy to reduce error rapidly at the beginning of adaptation 3 .…”