Figure 3.
Dose-dependent effect of D2-like activation on nonfocal plasticity induced by anodal and cathodal tDCS (experiment 1). The time course plots show the effect of different doses of RP on tDCS-induced nonfocal neuroplasticity. Shown are baseline-standardized MEP amplitudes after plasticity induction by cathodal and anodal tDCS under 0.125, 0.25, 0.5, and 1.0 mg of RP or PLC up to the evening of the poststimulation day. As shown by TMS-elicited MEP amplitudes, RP produced a biphasic response, where low (0.125 and 0.25 mg) and high (1.0 mg) dosages impaired both cathodal and anodal tDCS-induced neuroplasticity, compared with the placebo (PLC) condition. Under medium dosage (0.5 mg), RP does not influence the anodal tDCS-elicited aftereffects. In contrast, a prolonged inhibition was observed in the cathodal tDCS condition. Shown are the mean ± SEM amplitudes vs baseline across time following anodal or cathodal tDCS for 0.125 (A), 0.25 mg (B), 0.5 (C), and 1.0 mg (D) of RP and PLC conditions. Filled symbols indicate significant deviations of the post-tDCS MEP amplitudes from baseline values, and “#” symbols mark significant deviations of drug versus PLC conditions with regard to identical time points and tDCS polarities (Student's t test, two-tailed, paired samples, p < 0.05). ne, Next evening; nm, next morning; na, next afternoon; se, same evening.