Cerebellar tDCS Modulates Corticocortical Functional Networks in a Regionally Specific Manner

With extensive interconnections with the cerebral cortex, the cerebellum is well positioned to coordinate communication between cortical regions. Because different cerebellar subregions interconnect with distinct cortical networks, the impact of regional cerebellar activity should be network-specific. However, it is unclear whether or how cerebellar modulation impacts the functional connectivity (FC) of cerebral cortical networks. To test this, we randomly assigned adults (<i>n</i> = 33; 21.2 ± 3.1 years; 22 M/11 F) to undergo 20 min of 1.5 mA transcranial direct current stimulation (tDCS) targeting either the posterior midline (<i>n</i> = 17) or right posterolateral cerebellum (<i>n</i> = 16). Each participant received anodal (excitatory), cathodal (inhibitory) or sham tDCS during separate MRI sessions. We analyzed post-tDCS resting-state fMRI data to determine whether modulating different cerebellar subregions impacted resting-state FC of distinct cortical networks. Multivariate pattern analyses revealed that posterior midline tDCS primarily modulated FC in the default mode network (DMN), while posterolateral cerebellar tDCS altered FC in the frontoparietal network (FPN). Seed-based connectivity analyses confirmed that posterior midline modulation increased within-network DMN FC while decreasing FC between DMN, visual, and somatomotor networks. In contrast, posterolateral cerebellar tDCS strengthened frontoparietal and attentional network FC while decoupling FPN-DMN and FPN-visual networks. These results support the hypothesis that the cerebellum modulates corticocortical connectivity and further suggest that the posterior midline modulates the DMN, while the posterolateral cerebellum shifts the brain toward a task-ready cognitive state. These findings provide insight into how the cerebellum influences the cerebral cortex and have clinical implications for targeted interventions in neurological and psychiatric conditions.