Cerebellar tDCS differentially modulates sensory inputs in somatosensory cortex and cerebellum.

Cerebellar transcranial direct-current stimulation (Cb-tDCS) is a promising tool for non-invasive modulation of cerebellar activity and has been proposed for the treatment of cerebellum-related disorders. However, how external currents applied to the cerebellum affect local and distant circuits remains unclear. In this study, we examined the immediate and aftereffects of Cb-tDCS on sensory inputs recorded in the cerebellar Crus I/II and primary somatosensory cortex (S1) in response to whisker stimulation. We also assessed changes in the excitation/inhibition balance using vGLUT1 and GAD 65-67 immunoreactivity. Anodal and cathodal Cb-tDCS respectively induced an immediate increase and decrease in the trigeminal component in Crus I/II but no aftereffects were observed 20 minutes post-stimulation. In S1, Cb-tDCS resulted in polarity-dependent modulation of the N1 component during stimulation, which was opposite to the changes induced in Crus I/II and a sustained increase after anodal Cb-tDCS, accompanied by reduced GAD 65-67 immunoreactivity. While power spectrum analysis revealed no changes in Crus I/II, cathodal Cb-tDCS significantly modulated gamma (30-45 Hz) and high-frequency oscillations (255-300 Hz) in S1. These findings indicate that Cb-tDCS can modulate sensory inputs during stimulation and exert delayed effects in distant cortical areas, emphasizing the need to consider both online and remote network modulation in clinical applications.