Non-invasive brain stimulation can also be used to study the connection between the cerebellum and the motor cortex via using paired-pulse TMS. Specifically, cerebellar stimulation 5 ms before motor cortex stimulation leads to a reduction in the amplitude of motor-evoked potentials (MEPs), a phenomenon referred to as cerebellar-brain inhibition (CBI) (Pinto et al. 2001). This measure of CBI is abnormal in PD patients—it is reduced at rest, but increases with muscle contraction (Ni et al. 2010).