Polarity-dependent modulation of sensory circuits by cerebellar tDCS: local and distant effects

Cerebellar transcranial direct current stimulation (Cb-tDCS) is a promising tool for non-invasive modulation of cerebellar function and is under investigation for treating cerebellum-related disorders. However, its local and remote effects on sensory processing remain poorly understood. We investigated the immediate and long-term effects of Cb-tDCS on sensory-evoked responses in the cerebellum and primary somatosensory cortex (S1) of awake mice. Sensory-evoked potentials (SEPs) were recorded in Crus I/II and S1 during and after short (15 s) or long (20 min) sessions of anodal or cathodal Cb-tDCS. In addition, the excitation/inhibition balance was assessed by quantifying vGLUT1 and GAD 65-67 immunoreactivity, and spectral changes in local field potentials were analyzed using FFT-based analysis. 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 poststimulation. 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 show that Cb-tDCS differentially modulates sensory input processing in cerebellar and cortical circuits. While cerebellar effects are transient, stimulation elicits lasting changes in remote cortical areas. This underscores the need to consider both local and distant network effects when applying Cb-tDCS in translational and clinical settings.