EP 128. Motor learning: TDCS effects vary with baseline performance

Abstract

Transcranial direct current stimulation (tDCS) allows the non-invasive modulation of cortical excitability. Anodal tDCS is associated with an increase of cortical excitability, while cathodal tDCS yields its decrease. Beyond altered excitability, tDCS to the primary motor cortex (M1) has been proven to modulate motor performance, but effects considerably vary across participants. To further elucidate the indicative role of baseline performance on the impact of tDCS, we subdivided 72 participants after baseline reaction time recordings into fast and slow performers by median split. Subsequently, participants implicitly learned a motor sequence with the right hand using the serial reaction time task. M1 is assumed to contribute to motor sequence acquisition and early motor memory consolidation, while the premotor cortex (PMC) may be relevant for later phases of consolidation. In half of the participants, tDCS was applied to the left M1 and in the other half to the left PMC. Since tDCS effects also vary with respect to timing of stimulation, tDCS was applied either prior to or during motor sequence learning. Anodal vs. cathodal vs. sham tDCS was applied in three separate sessions. When tDCS was applied prior to learning, anodal M1 tDCS facilitated subsequent sequence acquisition. Most interestingly, this effect became evident in participants with slow baseline reaction times only. When tDCS was applied during learning, anodal M1 tDCS yielded an unspecific facilitation of reaction times – again in participants with slow baseline performance only. Cathodal and sham tDCS as well as PMC tDCS had no such effect. Fast performers did not benefit from tDCS possibly due to a ceiling effect. Beyond underpinning the relevance of M1 for initial motor sequence acquisition, the present results complement evidence that behavioural tDCS effects may strongly depend on the behavioural status quo at time of stimulation.