Exploring the effects of cerebellar tDCS on mental rotation.

Transcranial direct current stimulation (tDCS) on the prefrontal and posterior parietal cortex can enhance mental rotation (MR) performance, whereas little is known about cerebellar tDCS (ctDCS). This study aimed to evaluate effects of ctDCS on a MR task. Fifty-five healthy subjects were randomly assigned to active-ctDCS (1.5 mA; 20 min; n = 28) or sham-ctDCS (n = 27). Participants performed a MR task before (T0) and after (T1) stimulation. In each trial, two shapes appeared on a computer screen, one randomly rotated by 0, 45, 90, or 135 degrees. Subjects pressed the A or L key to indicate whether the shapes were identical or mirrored. A linear mixed model was run on the reaction times (RTs) recorded in each trial. Percent change in RTs (%RT) from T0 to T1 was also computed and analyzed using a second mixed-effects model with planned contrasts. A significant main effect of Time revealed RTs decreased from T0 (M = 3079.35, SE = 102.27) to T1 (M = 2565.36, SE = 102.27). No significant main effects or interactions involving Group were observed in either RT or %RT models. Planned contrasts revealed a single significant difference between groups in the 0° same condition, with the ctDCS group showing a greater reduction in %RT compared to the sham group. No other significant effects were found. ctDCS did not produce a global improvement in MR but showed selective effects under minimal spatial transformation demands. Further studies with different stimulation protocols are needed to clarify its role.