Cerebellar anodal transcranial direct current stimulation (tDCS) improves implicit mentalizing sequence learning: A double-blind sham-controlled study.

An increasing number of studies have revealed that the posterior cerebellum plays a vital role in mentalizing by identifying and learning social action sequences that render social interaction more fluent, coordinated, and predictable. An implicit social sequencing task, the Belief serial response time (SRT) task, was administered during and 30 min after targeting the cerebellum with anodal transcranial direct current stimulation (tDCS; 2 mA for 20 min, electrode 2 cm below the inion). In a previous study, this setup did not show significant improvement in response times. We reasoned that the familiar and overlearned nature of attributing social beliefs resulted in a ceiling effect and thus left very little margin for improvement on the task. The current study developed a more difficult version of the Belief SRT task. Using a double-blind sham-controlled protocol, 60 participants received either anodal tDCS or sham tDCS using the same stimulation protocol. Results showed that participants receiving anodal tDCS responded faster when the sequence of actions was repeated as opposed to totally randomized compared with participants who received sham tDCS. These findings suggest a positive effect of anodal cerebellar tDCS on implicit mentalizing sequence learning, supporting a causal role of the cerebellum in this learning process. This holds promise for treating clinical populations with limited social and sequencing capacities (e.g., autism) with anodal tDCS.