Neuromodulation of the Cerebellum for Motor Applications: A Systematic Review.

Background: Despite the connections and clear importance of the cerebellum in motor function, research utilizing cerebellar neuromodulation for treatment of movement disorders is still underdeveloped. Here we conduct a systematic review to investigate non-invasive neurostimulation of the cerebellum and its potential impact on motor systems and its function. Our aim is to give a general review of each neurostimulation study focusing on the cerebellum as a treatment target in the past five years at time of search, in order to update the field on current findings and inspire similar cerebellar neurostimulation research without unnecessary repetition.

Methods: Using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, our search included articles over the past five years that evaluated neurostimulation of the cerebellum (e.g., transcranial magnetic stimulation, transcranial direct current stimulation, and transcranial alternating current stimulation, etc.). Inclusion criteria included: (1) neurostimulation (repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS)) of the cerebellum; (2) only original articles, and (3) outcomes focused on motor functions. Exclusion criteria included: (1) neurostimulation with the goal of targeting any brain structure other than the cerebellum and (2) reviews and conference abstracts.

Results: The search revealed 82 distinct articles relevant to the research question. Included are 17 articles concerning rTMS, 56 articles concerning tDCS, and 9 articles concerning tACS. The majority of the studies are controlled trials of varying types, with 79, with two case studies and one pilot study.

Conclusions: Many studies showed significant effects on motor function and circuitry via non-invasive neurostimulation of the cerebellum. Common targets of cerebellar neurostimulation include visuomotor control, stroke rehabilitation for improvements in balance and coordination, and motor skill acquisition. The field is still exploring ideal parameters of neurostimulation for each disorder or function of interest. Future research areas should include the inclusion of individual anatomy, including functional connectivity, and improving stimulation selectivity.