Cathodal Transcranial Direct Current Stimulation (tDCS) Applied to the Left Premotor Cortex Interferes with Explicit Reproduction of a Motor Sequence.

Bettina Pollok,Vanessa Krause,Claire Schmitz-Justen

doi:10.3390/brainsci11020207

Abstract

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that allows the modulation of cortical excitability. TDCS effects can outlast the stimulation period presumably due to changes of GABA concentration which play a critical role in use-dependent plasticity. Consequently, tDCS and learning-related synaptic plasticity are assumed to share common mechanisms. Motor sequence learning has been related to activation changes within a cortico-subcortical network and findings from a meta-analysis point towards a core network comprising the cerebellum as well as the primary motor (M1) and the dorsolateral premotor cortex (dPMC). The latter has been particularly related to explicit motor learning by means of brain imaging techniques. We here test whether tDCS applied to the left dPMC affects the acquisition and reproduction of an explicitly learned motor sequence. To this end, 18 healthy volunteers received anodal, cathodal and sham tDCS to the left dPMC and were then trained on a serial reaction time task (SRTT) with their right hand. Immediately after the training and after overnight sleep, reproduction of the learned sequence was tested by means of reaction times as well as explicit recall. Regression analyses suggest that following cathodal tDCS reaction times at the end of the SRTT training-block explained a significant proportion of the number of correctly reported sequence items after overnight sleep. The present data suggest the left premotor cortex as one possible target for the application of non-invasive brain stimulation techniques in explicit motor sequence learning with the right hand.

Highlights

The ability to learn and retain movement sequences is crucial for numerous everyday actions
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The present findings indicate a significant inverse relation between reaction times in sequential trials at the end of the training (t2) and explicit reproduction of the learned sequence after overnight sleep following cathodal Transcranial direct current stimulation (tDCS)

Summary

Introduction

The ability to learn and retain movement sequences is crucial for numerous everyday actions. The most common paradigm for the investigation of motor sequence learning is the serial reaction time task (SRTT) originally introduced by Nissen and Bullemer [1]. In this task, the participants learn a sequence of keypresses in response to visual cues. Learning is indicated by reduced errors as well as shortening of reaction times during training on the task and can occur explicitly by informing the participants about the embedded sequence or implicitly through repeated practice (reviewed in [2,3,4,5,6,7]). Consolidation allows the transfer of an initially fragile movement pattern into a more robust state [13,14]; reviewed in [4,5,7,9,10,11,15,16]

Methods

Results

Conclusion