Effects of different electrical brain stimulation protocols on subcomponents of motor skill learning

Background: Noninvasive electrical brain stimulation (NEBS) with transcranial direct current (tDCS) or random noise stimulation (tRNS) applied to the primary motor cortex (M1) can augment motor learning.

Objective: We tested whether different types of stimulation alter particular aspects of learning a tracing task over three consecutive days, namely skill acquisition (online/within session effects) or consolidation (offline/between session effects).

Methods: Motor training on a tracing task over three consecutive days was combined with different types and montages of stimulation (tDCS, tRNS).

Results: Unilateral M1 stimulation using tRNS as well as unilateral and bilateral M1 tDCS all enhanced motor skill learning compared to sham stimulation. In all groups, this appeared to be driven by online effects without an additional offline effect. Unilateral tDCS resulted in large skill gains immediately following the onset of stimulation, while tRNS exerted more gradual effects. Control stimulation of the right temporal lobe did not enhance skill learning relative to sham.

Conclusions: The mechanisms of action of tDCS and tRNS are likely different. Hence, the time course of skill improvement within sessions could point to specific and temporally distinct interactions with the physiological process of motor skill learning. Exploring the parameters of NEBS on different tasks and in patients with brain injury will allow us to maximize the benefits of NEBS for neurorehabilitation.