Voluntary movements after chronic spinal cord injury
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Recently, a new study was published in Brain addressing electrical stimulation of the spinal cord after injury. The study was funded in part by the Christopher & Dana Reeve Foundation.
Claudia Angeli and co-workers published this study as a sequel of a single case study published by the same group around S. Harkema in 2011 in Lancet. Back then, electrodes were implanted in the spinal canal (epidural) of a chronically spinal cord injured patient (L1-S1). These electrodes are activated via a subcutaneous, abdominal neurostimulator (pulse generator). Additionally, the patient was subjected to very intense rehabilitation training. After many training sessions, he was able to perform voluntary movements of the paralyzed muscles.
This study was now expanded by further three patients, thus now recruiting motor and sensory completely paralyzed patients (AIS A), as well as motor complete, sensory incomplete patients (AIS B). All of them regained a certain degree of voluntary movement control of the lower limbs (and improved trunk stability) that hasn’t been achieved with previous rehabilitation techniques, so far. To verify the voluntary nature of the muscle reactions, the movements had to be conducted upon an acoustic or visual stimulus. In part, the stimulation frequency could be reduced with concomitant training sessions. One patient was then actually able to perform some movements without stimulation.
Long-term effects may also emerge in the future. However, this published study does not report any effects of the treatment on vegetative functions, e.g. control over bladder or bowel. No adverse effects are reported up to date.
The underlying mechanism is not completely understood. Researchers consider “silent” (i.e. inactive) nerve fibers along the spinal cord. The neurophysiological testing of nerve- and muscle activity before electrode implantation didn’t reveal any activity and these silent fibers could not be activated by common rehabilitation techniques. The stimulation with electrodes, however, might have re-activated and amplified them.
A further hypothesis suggests that - similar to some animals (e.g. cats) - there is also a local spinal center for movements in the lumbar vertebra of humans (central pattern generator, CPG). Upon sensory stimulation from the periphery, this existing network of spinal (inter-) neuronal connections can generate locomotive activity (partially) independently of the brain. Thus, epidural stimulation together with intensive training could have facilitated and amplified the activity of such a CPG.
This study is a milestone and showed that clinical completely paralyzed patients were able to perform voluntary movements to a certain degree when treated with a combination of epidural stimulation and intensive training units. To what extent this means improvements for the daily lives of patients needs to be clarified in future studies. These will also unravel if and when the results of this study can be translated to a therapy for chronic spinal injured patients.
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