Physiology of the motor cortex in polio survivors.
We hypothesized that the corticospinal system undergoes functional changes in long-term polio survivors. Central motor conduction times (CMCTs) to the four limbs were measured in 24 polio survivors using transcranial magnetic stimulation (TMS). Resting motor thresholds and CMCTs were normal. In 17 subjects whose legs were affected by polio and 13 healthy controls, single- and paired-pulse TMS was used to assess motor cortex excitability while recording from tibialis anterior (TA) muscles at rest and following maximal contraction until fatigue. In polio survivors the slope of the recruitment curve was normal, but maximal motor evoked potentials (MEPs) were larger than in controls. MEPs were depressed after fatiguing exercise. Three patients with central fatigue by twitch interpolation had a trend toward slower recovery. There was no association with symptoms of post-polio syndrome. These changes occurring after polio may allow the motor cortex to activate a greater proportion of the motor neurons innervating affected muscles.
Lupu
Vitalie D
VD
EMG Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Building 10, CRC, 7-5680, 10 Center Drive, MSC-1404 Bethesda, Maryland 20892, USA.
Danielian
Laura
L
Johnsen
Jacqueline A
JA
Vasconcelos
Olavo M
OM
Prokhorenko
Olga A
OA
Jabbari
Bahman
B
Campbell
William W
WW
Floeter
Mary Kay
MK
D000368:Aged; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005221:Fatigue; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology* / Q000821:virology; D018482:Muscle, Skeletal / Q000294:innervation; D009431:Neural Conduction / Q000502:physiology / Q000528:radiation effects; D009433:Neural Inhibition / Q000502:physiology / Q000528:radiation effects; D010807:Physical Endurance; D016262:Postpoliomyelitis Syndrome / Q000473:pathology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods