Introduction

CORTEX
Motor sequence learning, a type of procedural memory, is fundamental to daily living. It enables automation of frequently repeated activities, such as typing, cycling, or playing a musical instrument. Motor skills acquired through extensive repetition can subsequently be performed effortlessly [Anodal transcranial direct current stimulation (TDCS) is a non-invasive approach to modulating neural plasticity by lowering the neuronal firing threshold. It has been investigated as a means of modulating motor learning when delivered to CB or primary motor cortex (M1) [Here we focus specifically on implicit motor sequence learning, which is frequently assessed using the serial reaction time task (SRTT) [As the type of motor learning, the time point of evaluation relative to stimulation, as well as the stimulation type, parameters, and location contribute to variable findings [Studies so far reporting both CB-TDCS and M1-TDCS have employed different motor learning tasks, including motor sequence learning [To enable a direct comparison of the roles of the CB and M1 in implicit motor sequence learning, we used the same SRTT paradigm while stimulating each structure and during Sham. Crucially, the same number of repeated and random sequences were presented, enabling a direct comparison of performance, 12-item sequences were used to ensure that learning was implicit, and ipsilateral stimulation was applied to limit modulation of additional structures. Additionally, we took account of the potential susceptibility effect, which refers to the slower RTs initially observed during the learned sequence directly after responding to random sequences and is well-recognised in motor learning paradigms [