Fig. 2: Behavioural results.
From: Non-invasive stimulation of the human striatum disrupts reinforcement learning of motor skills
a, Motor performance across training. The raw Error data (expressed in percentage of maximum voluntary contraction (MVC)) from the 24 participants are presented in the left panel for the different experimental conditions in bins of four trials. The increase in Error during training is related to the visual uncertainty (that is, the intermittent disappearance of the cursor) that was applied to enhance reinforcement effects. The three plots on the right represent the pre-training normalized Error in the tTISSham, tTIS20Hz and tTIS80Hz blocks. Reinforcement-related benefits represent the improvement in the Error measured in the ReinfON and ReinfOFF blocks during training (reflecting benefits in motor performance) or at post-training (reflecting benefits in learning). b, Averaged learning across conditions. The violin plot shows the Error distribution at post-training (expressed in percentage of pre-training) averaged across conditions, as well as individual participant data. A single-sample two-sided t-test showed that the post-training Error was lower than the pre-training level, indicating significant learning in the task (P = 0.013; n = 24 participants). c, Motor learning. The averaged Error at post-training (normalized to pre-training) and the corresponding individual data points in the different experimental conditions are shown in the left and right panels, respectively, for the participants included in the analysis (that is, after outlier detection; remaining n = 23). The reduction of Error at post-training reflects true improvement at tracking the target in test conditions (in the absence of reinforcement, visual uncertainty or tTIS). The LMM run on these data revealed a specific effect of tTIS80Hz on reinforcement-related benefits in learning (analysis of variance (ANOVA) with Satterthwaite approximation followed by two-sided pairwise comparisons via estimated marginal means with Tukey adjustment). Learning was disrupted with ReinfON in the tTIS80Hz condition compared with the tTIS20Hz (P = 0.039) and tTISSham (P < 0.001) conditions. d, Motor performance. The averaged Error during training (normalized to pre-training) and the corresponding individual data points in the different experimental conditions are shown in the left and right panels, respectively, for the participants included in the analysis (that is, after outlier detection; n = 23). The Error change during training reflects the joint contribution of the experimental manipulations (visual uncertainty, potential reinforcement and tTIS) to motor performance. The LMM run on these data showed a frequency-dependent effect of tTIS on motor performance, irrespective of reinforcement (ANOVA with Satterthwaite approximation followed by two-sided pairwise comparisons via estimated marginal means with Tukey adjustment). Motor performance was disrupted irrespective of reinforcement in the tTIS20Hz (versus tTISSham: P < 0.001) and tTIS80Hz (versus tTISSham: P < 0.001; versus tTIS20Hz: P = 0.031) conditions. The data are represented as mean ± s.e.
