Forces consistent with plateau‐like behaviour of spinal neurons evoked in patients with spinal cord injuries

Percutaneous electrical stimulation over tibialis anterior and triceps surae was performed in 14 patients with traumatic spinal cord injury (SCI) to look for evidence that ‘extra contractions’ can develop, beyond those due to activation of the motor axons beneath the stimulating electrodes. Criteria...

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Bibliographic Details
Published in:Brain (London, England : 1878) England : 1878), 2004-03, Vol.127 (3), p.660-670
Main Authors: Nickolls, P., Collins, D. F., Gorman, R. B., Burke, David, Gandevia, S. C.
Format: Article
Language:English
Subjects:
Adolescent
Adult
Axons - physiology
Biological and medical sciences
Child
Electric Stimulation
Electromyography
EMG = electromyographic activity
Female
Humans
Leg
Male
Medical sciences
Middle Aged
Motor Neurons - physiology
Muscle Contraction
Muscle, Skeletal - physiopathology
Neurology
plateau potentials
SCI = spinal cord injury
Spinal Cord Injuries - physiopathology
spinal cord injury
TA = tibialis anterior
tibialis anterior
triceps surae
TS = triceps surae
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Summary:Percutaneous electrical stimulation over tibialis anterior and triceps surae was performed in 14 patients with traumatic spinal cord injury (SCI) to look for evidence that ‘extra contractions’ can develop, beyond those due to activation of the motor axons beneath the stimulating electrodes. Criteria for the extra contractions included marked asymmetry of force with respect to stimulation, progressively rising force during stimulation of constant amplitude and frequency, and force remaining high after stimulation frequency had returned to the control level following a high‐frequency burst. Twelve of the 14 patients showed evidence of such behaviour, more frequently in triceps surae than tibialis anterior. Force or electromyographic activity commonly outlasted the stimulation in these patients. There was no apparent correlation between the completeness or level of injury and the ability to induce the behaviour. Evidence of force potentiation and ‘habituation’ was also seen. Eleven of the 14 patients exhibited hyper‐reflexia and reported spontaneous spasms, but there was no obvious association with the extra contractions. It is concluded that non‐classical behaviour of neurons within the spinal cord can contribute to the extra contractions evoked by electrical stimulation over muscles in spinal cord‐injured subjects. This central contribution is less easy to obtain than in intact healthy subjects, all of whom showed the phenomenon. These contractions are consistent with the activation of plateau potentials in spinal neurons and, if so, plateau potentials may contribute to a patient’s clinical manifestations.
ISSN:0006-8950
1460-2156
1460-2156
DOI:10.1093/brain/awh073