# Differential Effects of Cerebellar tDCS on Sequential Mentalizing

## TL;DR

This study shows that cerebellar tDCS can influence how quickly people learn to process complex social sequences, with anodal stimulation improving performance.

## Contribution

The study introduces a novel focal montage of cerebellar tDCS and demonstrates its differential effects on social sequence learning.

## Key findings

- Anodal tDCS significantly improved reaction times in the second session, suggesting enhanced sequence learning.
- Cathodal tDCS did not affect performance, while sham tDCS showed improvement in the third session.
- The interaction between stimulation type and session highlights the cerebellum's role in social learning processes.

## Abstract

The cerebellum has been increasingly recognized for its role in social cognition, particularly in mentalizing processes. A way to measure mentalizing is the picture sequencing task, a well-established measure of social action sequencing during mentalizing of other’s beliefs. Recent studies have shown that cerebellar transcranial direct current stimulation can affect social sequence processing in adults, however, the effects of different types of stimulation remain unclear. Therefore, in this study, we examined the effects of a novel and more focal montage of cerebellar tDCS on the picture sequencing task in healthy adults. Using a within-participant design, 35 participants completed three sessions in which they underwent anodal, cathodal, and sham stimulation (in a counterbalanced order). Results revealed that participants were consistently slower on sequences that required complex mentalizing compared to well-known social situations and non-social events. Anodal tDCS significantly speeded up reaction times from the second session (indicating an improvement in performance), sham tDCS showed the same improvement in the third session (indicating general improved familiarity with the task), while cathodal tDCS did not change performance. This interaction between stimulation type and session suggests that anodal tDCS may accelerate sequence learning, while cathodal tDCS may inhibit it. Accuracy results reflected a similar pattern, with improvements over time driven by the stimulation-learning interaction. In conclusion, cerebellar tDCS modulates performance with anodal stimulation enhancing processing speed and learning. More importantly, the interaction between the different types of stimulation and learning reinforces the importance of the cerebellum in social learning processes.