Increased cortical excitability induced by transcranial DC and peripheral nerve stimulation.

This study investigated the effect of short periods of simultaneous weak anodal direct current (DC) stimulation and peripheral ulnar nerve (ES) stimulation on corticospinal excitability. The experiments involved repeated testing of ten normal subjects with four different protocols: (1) No Stimulation; (2) DC only; (3) ES only; (4) DC plus ES. Motor evoked potentials (MEP) were recorded from the First Dorsal Interosseous (FDI); Abductor Digiti Minimi (ADM) and Flexor Carpi Ulnaris (FCU). The baseline MEP amplitude was compared with that obtained immediately after the first set of stimulation, after the second set of stimulation, 15 min post stimulation and 30 min after stimulation. No significant change was seen with the No Stimulation and ES Only protocols. FDI showed a significant change in the DC protocol after the second set of stimulation but the changes were not present 15 or 30 min after. The DC plus ES protocol showed FDI changes that were significant after the second set of stimulation with the elevations persisting when tested 15 and 30 min post intervention. These observations show that a period of anodal DC stimulation preceding a period of ulnar nerve stimulation resulted in significant and persistent elevations in cortical excitability.