Understanding cerebellar cognitive and social functions: methodological challenges and new directions for future transcranial magnetic stimulation studies

New Perspectives on Non-Invasive Cerebellar Stimulation for Social and Affective Functions in Children and Adolescents

Cerebellar dysfunction affects socio-affective abilities beyond motor control. Recent studies suggest that non-invasive cerebellar neurostimulation can modulate social cognition networks, offering potential therapeutic benefits for children with autism, ADHD, and mood disorders. However, its application in pediatrics remains largely unexplored. This review summarizes emerging pediatric research on cerebellar transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS). We discuss their mechanisms, potential benefits, and safety considerations, highlighting preliminary findings that suggest feasibility and effectiveness. Ethical concerns and technical challenges related to pediatric neuroanatomy and stimulation parameters are also addressed. While early results are promising, further clinical trials and neurophysiological studies are essential to optimize protocols and confirm long-term efficacy. Advancing our understanding of cerebellar involvement in socio-affective functions could lead to innovative rehabilitation strategies for neurodevelopmental disorders.

The cerebellum contributes to prediction error coding in reinforcement learning in humans

Recent rodent data suggest that the cerebellum - a region typically associated with processing sensory prediction errors (PEs) - also processes PEs in reinforcement learning (RL-PEs; i.e., learning from action outcomes). We tested whether cerebellar output is necessary for RL-PE processing in regions more traditionally associated with action-outcome processing, such as striatum and anterior cingulate cortex. The feedback-related negativity (FRN) was measured as a proxy of cerebral RL-PE processing in a probabilistic feedback learning task using electroencephalography. Two complementary experiments were performed in humans. First, patients with chronic cerebellar stroke (20 male, 6 female) and matched healthy controls (19 male, 7 female) were tested. Second, single-pulse cerebellar transcranial magnetic stimulation (TMS) was applied in healthy participants (7 male, 17 female), thus implementing a virtual lesion approach. Consistent with previous studies, learning of action-outcome associations was intact with only minor changes in behavioural flexibility. Importantly, no significant RL-PE processing was observed in the FRN in patients with cerebellar stroke, and in participants receiving cerebellar TMS. Findings in both experiments show that RL-PE processing in the forebrain depends on cerebellar output in humans, complementing and extending previous findings in rodents.Significance statement While processing of prediction errors in reinforcement learning (RL-PEs) is usually attributed to midbrain and forebrain, recent rodent studies have recorded RL-PE signals in the cerebellum. It is not yet clear whether these cerebellar RL-PE signals contribute to RL-PE processing in the forebrain/midbrain. In the current study, we could show that forebrain RL-PE coding is blunted when the cerebellum is affected across two complementary lesion models (patients with cerebellar stroke, cerebellar TMS). Our results support direct involvement of the cerebellum in RL-PE processing. We can further show that the cerebellum is necessary for RL-PE coding in the forebrain.

The Past, Current and Future Research in Cerebellar TMS Evoked Responses-A Narrative Review

Transcranial magnetic stimulation coupled with electroencephalography (TMS-EEG) is a novel technique to investigate cortical physiology in health and disease. The cerebellum has recently gained attention as a possible new hotspot in the field of TMS-EEG, with several reports published recently. However, EEG responses obtained by cerebellar stimulation vary considerably across the literature, possibly due to different experimental methods. Compared to conventional TMS-EEG, which involves stimulation of the cortex, cerebellar TMS-EEG presents some technical difficulties, including strong muscle twitches in the neck area and a loud TMS click when double-cone coils are used, resulting in contamination of responses by electromyographic activity and sensory potentials. Understanding technical difficulties and limitations is essential for the development of cerebellar TMS-EEG research. In this review, we summarize findings of cerebellar TMS-EEG studies, highlighting limitations in experimental design and potential issues that can result in discrepancies between experimental outcomes. Lastly, we propose a possible direction for academic and clinical research with cerebellar TMS-EEG.