After vs. priming effects of anodal transcranial direct current stimulation on upper extremity motor recovery in patients with subacute stroke

Purpose: Transcranial direct current stimulation (tDCS) of the motor cortex seems to be effective in improving motor performance in patients with chronic stroke, while some recent findings have reported conflicting results for the subacute phase. We aimed to verify whether upper extremity motor rehabilitation could be enhanced by treatment with tDCS administered before a rehabilitative session. Methods: Hand dexterity and force in 16 individuals with subacute stroke were assessed before (T0) and after anodal stimulation (T1) and after a successive session of motor rehabilitation (T2) in a double-blind, randomized, sham-controlled, crossover trial. To confirm the value of the device as a specific effector, behavioral tests were also administered. Results: Anodal and sham stimulation plus rehabilitation significantly improved manual dexterity (repeated-measure Anova: A-tDCS: p = 0.005; S-tDCS: p = 0.042). Post hoc analysis revealed a significant stimulation effect only for A-tDCS (p = 0.013 between T0 and T1) and not for S-tDCS, whereas the rehabilitation effect (between T1 and T2) was not significant in either group. Hand force and behavioral features were unchanged. Conclusions: Anodal brain stimulation improves hand dexterity but does not increase the effectiveness of the rehabilitation directly. These results suggest the presence of aftereffects, not priming effects, of A-tDCS superimposed onto motor learning phenomena.