Brain State-Dependent Transcranial Magnetic Closed-Loop Stimulation Controlled by Sensorimotor Desynchronization Induces Robust Increase of Corticospinal Excitability.

Abstract

Desynchronization of sensorimotor rhythmic activity increases instantaneous corticospinal excitability, as indexed by amplitudes of motor-evoked potentials (MEP) elicited by transcranial magnetic stimulation (TMS). The accumulative effect of cortical stimulation in conjunction with sensorimotor desynchronization is, however, unclear. The aim of this study was to investigate the effects of repetitive pairing event-related desynchronization (ERD) with TMS of the precentral gyrus on corticospinal excitability. Closed-loop single-pulse TMS was controlled by beta-band (16-22 Hz) ERD during motor-imagery of finger extension and applied within a brain-computer interface environment in eleven healthy subjects. The same number and pattern of stimuli were applied in a control group of eleven subjects during rest, i.e. independent of ERD. To probe for plasticity resistant to depotentiation, stimulation protocols were followed by a depotentiation task. Brain state-dependent application of approximately 300 TMS pulses during beta-ERD resulted in a significant increase of corticospinal excitability. By contrast, the identical stimulation pattern applied independent of beta-ERD in the control experiment resulted in a decrease of corticospinal excitability. These effects persisted beyond the period of stimulation and the depotentiation task. These results could be instrumental in developing new therapeutic approaches such as the application of closed-loop stimulation in the context of neurorehabilitation.