Figure 6.

The role of positive-feedback reward signals to learning via use-dependent plasticity (UDP). (A) Schematic of an experimental task that assess UDP. Transcranial magnetic stimulation (TMS) is delivered over the left M1 to elicit thumb movements before and after training. The direction of TMS-evoked thumb movements was recorded and the proportion of TMS-evoked thumb movements falling in the training direction zone (TDZ; magenta) are measured. (B) Representative subject data displaying TMS-evoked thumb movements before (gray, left) and after (blue, middle) training. Mawase and others calculated the group average depicting the probability distribution of the thumb directions before and after task performance. Individuals who trained on this paradigm showed a significant increase in the proportion of TMS-evoked thumb movements within the TDZ. (C) The study design and setup of experiment 2 used in Mawase and others (2018) in which the authors showed that explicit rewards modulate UDP. In short, participants were randomly assigned to either a reward-group or random-reward group. Importantly, only the reward-group (blue) received explicit reward coinciding with task success, whereas the random reward group (red) received an explicit reward randomly throughout performance, independent of task success. TMS-evoked thumb movements were assessed before and after training for both groups. (D) A 2-dimensional histogram showing the total number of TMS-evoked movements for all participants, separated by group. Here, only the reward-group significantly benefited from receiving meaningful reward as they showed a dramatic change in TMS-evoked thumb movement direction, whereas the random-reward group did not show a significant change from baseline. Figures adapted from Mawase and others 2017; https://dx.doi.org/10.1523/jneurosci.3303-16.2017.