The effect of transcranial direct current stimulation on motor sequence learning and upper limb function after stroke.

Objective: To assess the impact of electrode arrangement on the efficacy of tDCS in stroke survivors and determine whether changes in transcallosal inhibition (TCI) underlie improvements.

Methods: 24 stroke survivors (3-124months post-stroke) with upper limb impairment participated. They received blinded tDCS during a motor sequence learning task, requiring the paretic arm to direct a cursor to illuminating targets on a monitor. Four tDCS conditions were studied (crossover); anodal to ipsilesional M1, cathodal to contralesional M1, bihemispheric, sham. The Jebsen Taylor hand function test (JTT) was assessed pre- and post-stimulation and TCI assessed as the ipsilateral silent period (iSP) duration using transcranial magnetic stimulation.

Results: The time to react to target illumination reduced with learning of the movement sequence, irrespective of tDCS condition (p>0.1). JTT performance improved after unilateral tDCS (anodal or cathodal) compared with sham (p<0.05), but not after bihemispheric (p>0.1). There was no effect of tDCS on change in iSP duration (p>0.1).

Conclusions: Unilateral tDCS is effective for improving JTT performance, but not motor sequence learning.

Significance: This has implications for the design of future clinical trials.