High-frequency repetitive transcranial magnetic stimulation to the cerebellum and implicit processing of happy facial expressions

Background: Previous research has demonstrated that the cerebellum is involved in emotive and cognitive processes. Furthermore, recent findings suggest high-frequency repetitive transcranial magnetic stimulation (rTMS) to the cerebellum has mood-improving properties. We sought to further explore the effects of cerebellar high-frequency rTMS on implicit processing of emotional stimuli and mood. Methods: In a double-blind, crossover study, 15 healthy volunteers received 15 minutes of 20 Hz (5 s on, 5 s off) rTMS over the medial cerebellum, occipital cortex or sham in a randomized counterbalanced order on 3 consecutive days. A masked emotional faces response task measured implicit emotional processing of happy, fearful and neutral facial expressions. We used positive and negative affect scales to evaluate rTMS-related changes in mood. Results: High-frequency rTMS over the cerebellum was associated with significant increases in masked emotional responses to happy facial expressions only. We observed no changes in consciously experienced mood. Limitations: Although the sham rTMS served as our baseline measurement, additional pre-rTMS data showing that reaction time increases immediately after cerebellar rTMS would have made our results more compelling. Conclusion: The results replicate and extend previous findings by establishing a direct relation between the cerebellum and emotive information-processing. The parallel between the present effects of high-frequency cerebellar rTMS and short-term antidepressant therapy regarding the change in implicit processing of positive stimuli in the absence of mood changes is notable and warrants further research.