Functional cerebellar connectomes interfacing motor adaptation and reinforcement feedback
Motor adaptation is driven by sensory prediction errors, yet reinforcement feedback can alter the speed and retention of adaptive behaviors. The cerebellum is central in motor adaptation, but posterior lobules, especially Lobule VI (CB6) and Crus I (CBcrus1), also participate in reinforcement-related signaling. Serotoninergic and dopaminergic systems, key modulators of motivational processes, directly influence cerebellar activity. However, how these neuromodulatory systems contribute to cerebellar network organization and to reinforcement-based adaptation in humans remains unclear. We employed a multimodal framework (Receptor-Enriched Analysis of functional Connectivity by Targets; REACT) using PET-derived Serotonin/Dopamine Transporter (SERT/DAT) templates to enrich resting-state functional Magnetic Resonance Imaging (rs-fMRI). We estimated SERT- and DAT-enriched functional connectivity from CB6 and CBcrus1 within motor-adaptation and reinforcement-learning networks, and tested their correlations with performance in a visuomotor adaptation task completed under reward and punishment. Our findings show lobule-specific neuromodulatory organization within the cerebellum. CB6 exhibited predominantly DAT- and SERT-enriched connectivity with motor adaptation networks, while CBcrus1 showed stronger SERT-enriched communication extending to both motor and reinforcement networks. Crucially, distinct cerebello-cortical neuromodulatory networks predicted individual differences in adaptation rate. DAT-enriched CBcrus1 connectivity was linked to punishment-driven adaptation, whereas SERT-enriched cerebello-orbitofrontal connectivity predicted faster adaptation across both reward and punishment contingencies. Furthermore, we observed overlaps between SERT- and DAT-enriched networks in the medial orbitofrontal area for Crus I, which predicted retention following punishment, underscoring the role of convergent neuromodulation in stabilizing adapted movements. We conclude that partially segregated yet convergent cerebello-cortical networks support interactions between motor and motivational behaviors, with combined and opposing effects of serotonergic and dopaminergic neuromodulation accounting for the speed and retention of adaptive behaviors.