Bi-directional modulation of somatosensory mismatch negativity with transcranial direct current stimulation: an event related potential study.

Appropriate orientation towards potentially salient novel environmental stimuli requires a system capable of detecting change in the sensorium. Mismatch negativity (MMN), an evoked potential calculated by subtracting the response to a standard repeated stimulus and a rare 'oddball' stimulus, is proposed as such a change detection mechanism. It is most widely studied in the auditory domain, but here we chose to explore the mechanism of somatosensory MMN, and specifically its dependence on the cerebellum. We recorded event-related potentials (ERPs) evoked in response to auditory and sensory stimuli from 10 healthy subjects before and after anodal, cathodal and sham transcranial direct current stimulation (tDCS) of the right cerebellar hemisphere. There was a significant increase in peak amplitude of somatosensory MMN after anodal tDCS (F(1,9) = 8.98, P < 0.02, mean difference anodal pre-post: -1.02 μV) and a significant reduction in peak amplitude of somatosensory MMN after cathodal tDCS (F(1,9) = 7.15, P < 0.03, mean difference cathodal pre-post: 0.65 μV). The amplitude of auditory MMN was unchanged by tDCS. These results reveal the capability of tDCS to cause bidirectional modulation of somatosensory MMN and the dependence of somatosensory MMN on the cerebellum.