Theta-tACS Modulates Cerebellar-Related Motor Functions and Cerebellar-Cortical Connectivity

Objective: To evaluate the effects of cerebellar transcranial alternating current stimulation (tACS) delivered at cerebellar -resonant frequencies, i.e., theta (0) and gamma (7), on upper limb motor performance and cerebellum -primary motor cortex (M1) connectivity, as assessed by cerebellar -brain inhibition (CBI), in healthy subjects. Methods: Participants underwent cerebellar-tACS while performing three cerebellar -dependent motor tasks: (i) rhythmic finger -tapping, (ii) arm reaching -to -grasp ('grasping') and (iii) arm reaching -topoint ('pointing') an object. Also, we evaluated possible changes in CBI during cerebellar-tACS. Results: 0-tACS decreased movement regularity during the tapping task and increased the duration of the pointing task compared to sham- and 7-tACS. Additionally, 0-tACS increased the CBI effectiveness (greater inhibition). The effect of 0-tACS on movement rhythm correlated with CBI changes and less tapping regularity corresponded to greater CBI. Conclusions: Cerebellar-tACS delivered at the 0 frequency modulates cerebellar -related motor behavior and this effect is, at least in part, mediated by changes in the cerebellar inhibitory output onto M1. The effects of 0-tACS may be due to the modulation of cerebellar neurons that resonate to the 0 rhythm. Significance: These findings contribute to a better understanding of the physiological mechanisms of motor control and provide new evidence on cerebellar non-invasive brain stimulation. (c) 2023 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).