Understanding and modulating motor learning with cerebellar stimulation.

Non-invasive brain stimulation techniques are a powerful approach to investigate the physiology and function of the central nervous system. Recent years have seen numerous investigations delivering transcranial magnetic stimulation (TMS) and or transcranial direct current stimulation (tDCS) to the cerebellum to determine its role in motor, cognitive and emotional behaviours. Early studies have shown that it is possible to assess cerebellar-motor cortex (CB-M1) connectivity using a paired-pulse TMS paradigm called cerebellar inhibition (CBI), and indirectly infer the state of cerebellar excitability. Thus, it has been shown that CBI changes proportionally to the magnitude of locomotor learning and in association with reaching adaption tasks. In addition, CBI has been used to demonstrate at a physiological level the effects of applying TMS or tDCS to modulate, up or down, the excitability of cerebellar-M1 connectivity. These studies became the fundamental substrate to newer investigations showing that we can affect motor, cognitive and emotional behaviour when targeting the cerebellum with TMS or tDCS in the context of performance. Furthermore, newer investigations are starting to report the effects of cerebellar non-invasive stimulation to treat symptoms associated with neurological conditions such as stroke and dystonia. Altogether, given the scarcity of current effective therapeutic options, non-invasive cerebellar stimulation can potentially become a game changer for the management of conditions that affect the cerebellum. This brief manuscript presents some of the current evidence demonstrating the effects of cerebellar stimulation to modulate motor behaviour and its use to assess physiological processes underlying motor learning.