Cerebellar Transcranial Direct Current Stimulation Induces a Predominant Motor Rather than Perceptive Contribution to Emotion Facial Expression Processing

Background: The cerebellum has recently been proposed as a key contributor to facial expression (FE) processing, although the neural pathways underlying its involvement remain poorly understood. This study investigated whether cerebellar modulation of FE processing preferentially relies on motor or perceptual circuits. Methods: Sixteen healthy young participants underwent cerebellar cathodal transcranial direct current stimulation (tDCs) and sham stimulation in a randomized crossover design. Cerebellar–motor cortex interactions were assessed using cerebellar brain inhibition (CBI) measured by a paired-pulse transcranial magnetic stimulation protocol, while early perceptual processing was evaluated through P100 and N170 event-related potentials (ERPs). Behavioral performance was assessed using a task involving recognition of neutral, happy, and fearful faces. Results: Cerebellar tDCs selectively modulated the cerebello–thalamo–primary motor cortex pathway, producing a significant reduction in CBI during the passive viewing of emotional (happy and fearful) expressions while exerting no significant effects on occipitotemporal ERP components associated with early face perception or on behavioral measures of emotion recognition, including recognition accuracy and reaction times. Conclusions: These findings indicate that cerebellar contributions to facial emotion processing are predominantly mediated through motor rather than early perceptual pathways. The cerebellum appears to modulate motor network activity during emotional face observation without directly influencing occipitotemporal perceptual mechanisms, although this physiological modulation was not accompanied by measurable changes in behavioral performance. These findings support the hypothesis that cerebellar involvement in social cognition is primarily related to the optimization of emotion-related motor processing.