Hypothesis
Cerebellar stimulation should increase implicit, error-based visuomotor adaptation and prefrontal stimulation should facilitate explicit, strategy-based learning, dissociating the two mechanisms.
What failed
Cerebellar stimulation had no effect on target error or implicit learning in a horizontal adaptation task and only weak effects in a vertical one, while the prefrontal benefit found in the first experiment did not replicate in the second; inter-individual variability was high, with a few individuals driving the group effects, and task context alone (vertical against horizontal screen) changed performance and the implicit contribution.
Broken assumption
Stimulating a region selectively enhances the learning process attributed to it.
Why
The authors conclude the effects of each region are strongly context-dependent and not cleanly dissociable, and call for work on the sources of individual variability.
From the published paper: Liew et al. Frontiers in Neuroscience, 2018. ↗CC BY