Brain stimulation studies of non-motor cerebellar function: A systematic review

• We review all cerebellar non-motor non-invasive stimulation studies.
• Effects seen in learning, memory, cognition, emotions, perception and timing.
• Diversity seen in stimulation parameters and targets despite similar tasks.
• Neuronavigation approaches shown to be beneficial.
• Improved understanding of physiology of stimulation essential.

Evidence for a cerebellar role in non-motor functions has been demonstrated by clinical and neuroimaging research. These approaches do not allow causal relationships to be inferred though the experimental manipulation of the cerebellum. Transcranial magnetic and current stimulation may allow better understanding of the cerebellum via the temporary alteration of its operation in healthy volunteers. This review examined all studies of the cerebellar role in non-motor functions using non-invasive brain stimulation. Of 7585 papers captured by an initial search, 26 met specific selection criteria. Analysis revealed behavioural effects across learning, memory, cognition, emotional processing, perception and timing, though the results were not sufficiently similar as to offer a definitive statement of the cerebellum's role. The non-invasive application of stimulation to the cerebellum presents challenges due to surrounding anatomy and the relatively small target areas involved. This review analysed the methods used to address these challenges with a view to suggesting methodological improvements for the establishment of standards for the location of cerebellar stimulation targets and appropriate levels of stimulation.