Abstract:
Priming the brain may provide potential treatment strategies for neurological disorders and stroke. Mesh glove stimulation (MGS) provides a non-motor target for rehabilitation. Following 30 minutes of suprasensory threshold MGS there is an increase in corticomotor excitability that is likely mediated by long-term potentiation. Transcranial direct current stimulation (tDCS) of the primary motor cortex can induce global changes in corticomotor excitability. Nine minutes of cathodal tDCS (c-tDCS) produces a lasting decrease in corticomotor excitability mediated by long-term depression. Whether priming MGS with c-tDCS further enhances corticomotor excitability through homeostatic metaplasticity mechanisms is unknown. Sixteen right-handed neurologically healthy individuals (9 female, 19-36 years) participated in a repeated measures cross-over study, nine minutes of sham- or c-tDCS followed by 30 minutes of suprasensory threshold MGS. Single-pulse transcranial magnetic stimulation (rest motor threshold and motor evoked potential amplitude), paired-pulse transcranial magnetic stimulation (intracortical facilitation, short afferent inhibition (SAI), short interval intracortical inhibition (SICI), and SAI with SICI (SAIxSICI)), and motor performance (grooved pegboard test) of the left hand were obtained at baseline, post-tDCS, and immediately, 30 and 60 minutes post-MGS. There was more disinhibition of SAI, and an increase in rest motor threshold and SAIxSICI after MGS was primed with c-tDCS compared with sham-tDCS. There was also a greater improvement in the grooved pegboard task after c-tDCS primed MGS than sham. Our results indicate a non-homeostatic metaplastic modulation of corticomotor excitability with c-tDCS primed MGS. Consequently, c-tDCS did not modulate corticomotor excitability after MGS, but did improve motor performance. Therefore, c-tDCS may be an effective priming modality to induce non-homeostatic metaplasticity.
