Facilitation of Corticospinal Connections in Able-bodied People and People With Central Nervous System Disorders Using Eight Interventions

Background: Voluntary contractions (VOL), functional electrical stimulation (FES), and transcranial magnetic stimulation (TMS) can facilitate corticospinal connections. Objective: To find the best methods for increasing corticospinal excitability by testing eight combinations: (1) VOL, (2) FES, (3) FES + VOL, (4) TMS, (5) TMS + VOL, (6) paired associative stimulation (PAS) consisting of FES + TMS, (7) PAS + VOL, and (8) double-pulse TMS + VOL. Methods: Interventions were applied for 3 x 10 minutes in 15 able-bodied subjects, 14 subjects with stable central nervous system lesions (e.g., chronic stroke, and incomplete spinal cord injury) and 16 subjects with progressive central nervous system conditions (e.g., secondary progressive multiple sclerosis). Motor-evoked potentials (MEP), M-waves, and H-reflexes were monitored over a 1-hour period. Results: Three interventions (PAS, PAS + VOL, and double-pulse TMS + VOL) caused 15% to 20% increases (P < 0.05) in the MEP at a stimulus level that initially produced a half-maximal response (MEPhalf) during a contraction. Interventions were less effective in both clinical groups than in the able-bodied group. Interventions with VOL were more effective in increasing the MEPhalf than those without (P = 0.022). When more modalities were combined, the MEP increases were larger (P = 0.022). Conclusions: (1) Short-term application of FES, TMS, and VOL can facilitate corticospinal pathways, particularly when methods are combined. (2) The effects may depend on the total activation of neural pathways, which is reduced in central nervous system disorders.