The primary motor cortex is associated with learning the absolute, but not relative, timing dimension of a task: A tDCS study

•Consistency and adaptability are characteristics of the skilled behavior.•Primary motor cortex (M1) may be more involved in the learning of the adaptability.•We stimulate M1 to facilitate motor learning.•The stimulation of M1 affected more the acquisition of motor adaptability.

The functional role of the primary motor cortex (M1) in the production of movement parameters, such as length, direction and force, is well known; however, whether M1 is associated with the parametric adjustments in the absolute timing dimension of the task remains unknown. Previous studies have not applied tasks and analyses that could separate the absolute (variant) and relative (invariant) dimensions. We applied transcranial direct current stimulation (tDCS) to M1 before motor practice to facilitate motor learning. A sequential key-pressing task was practiced with two goals: learning the relative timing dimension and learning the absolute timing dimension. All effects of the stimulation of M1 were observed only in the absolute dimension of the task. Mainly, the stimulation was associated with better performance in the transfer test in the absolute dimension. Taken together, our results indicate that M1 is an important area for learning the absolute timing dimension of a motor sequence.