Corticospinal excitability after continuous and intermittent theta burst stimulation applied on the lateral cerebellum: a study on healthy individuals

Abstract

To investigate the effects of continuous (cTBS) and intermittent (iTBS) theta burst stimulation applied over the lateral cerebellum on corticospinal excitability in healthy individuals. Methods: Twenty right-handed healthy male participants underwent three TBS sessions (cTBS, iTBS, sham) in a randomized crossover design. Motor evoked potentials (MEPs), resting and active motor threshold (RMT and AMT, respectively), and cortical silent period (CSP) were assessed before and after each session using single-pulse transcranial magnetic stimulation over the left primary motor cortex. Transcranial magnetic stimulation was delivered to the right cerebellar hemisphere at 80% of active motor threshold. Results: A significant reduction in MEP amplitude was observed following iTBS (p=0.028), while no significant changes occurred after cTBS or sham stimulation. No significant effects were found in RMT or CSP across any of the protocols. All sessions were well tolerated and considered safe. Mild and transient side effects, such as neck discomfort or headache, were reported in five participants. Conclusion: Intermittent cerebellar TBS was associated with reduced MEP amplitude, suggesting decreased corticospinal excitability, whereas cTBS and sham stimulation did not produce significant effects. Cerebellar TBS was safe and well tolerated in all participants. These findings suggest that cerebellar iTBS may exert modulatory effects on motor cortical excitability and may contribute to a better understanding of cerebellar stimulation effects in healthy individuals.