Decreased cortical excitability during motor imagery after disuse of an upper limb in humans.
OBJECTIVE
The present study investigated the effect of joint immobilization on corticomotoneuronal excitability to only intracortical input from a hierarchical level above the primary motor cortex.


METHODS
Motor evoked potentials (MEPs) and H-reflexes in the flexor carpi radialis muscle were elicited from 8 orthopedic patients with splints and 8 healthy volunteers. Each patient was examined on the day of splint removal (disuse stage) and 2 months after that day (recovery stage). Both potentials were recorded under 3 conditions: at rest, while imagining motor movement (during motor imagery), and during 10% of maximum voluntary contraction (10% MVC).


RESULTS
In the patient group, the amplitude of surface electromyography during voluntary maximum wrist flexion was lower at the disuse stage than at the recovery stage, although the supra-maximum M-wave amplitude did not change between stages. Compared to both the patient group at the recovery stage and the control group, patients at the disuse stage recorded significantly lower MEPs, but only during motor imagery. In contrast, the H-reflex amplitudes were not significantly changed under any of the 3 conditions for both patients and control.


CONCLUSIONS
The present results indicated a strict parallelism between motor execution (the reduction of electromyography during mvc after immobilization) and motor imagery (the reduction of MEP-amps after immobilization). This parallelism suggests that a functional reorganization or decreased excitability in the cerebral cortex area involved in executing movement likely decreases the motor capability to produce voluntary muscular output after immobilization.
Kaneko
Fuminari
F
Neuromuscular Assistive Technology Group, Institute for Human Science and Biomedical Engineering, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan. f-kaneko@aist.go.jp
Murakami
Tsuneji
T
Onari
Kiyoshi
K
Kurumadani
Hiroshi
H
Kawaguchi
Kotaro
K
D000328:Adult; D001132:Arm; D002370:Casts, Surgical; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor; D006181:H-Reflex; D006801:Humans; D007092:Imagination / Q000502:physiology*; D007103:Immobilization / Q000009:adverse effects*; D008280:Magnetics; D009044:Motor Cortex / Q000503:physiopathology*; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction; D014836:Volition / Q000502:physiology