Original Article: C. A. Angeli, V. R. Edgerton, Y. P. Gerasimenko and S. J. Harkema (2014). Altering spinal cord excitability enables voluntary movements after chronic complete paralysis in humans. Brain, 137(5), 1394-1409. Find the original article here.
Complete paralysis is the absence of motor control and sensation below the level of injury (lesion) on the spinal cord. Historically it was thought that regaining voluntary motor control below the lesion,while the spinal cord is electrically stimulated, two years after injury was very unlikely. Complete paralysis can limit recovery strategies and negatively affect an individual’s attitude towards their outcome. The direction of the current research has presumed that the solution to paralysis is the regeneration of axons (a component of nerve fiber) across the lesion; however, an effective rehabilitative treatment that elicits voluntary muscle control has yet to be discovered.
Researchers at the University of Louisville recently published a paper describing a study they conducted to investigate the effectiveness of standing training with epidural stimulation (ES) to stimulate the spinal cord, which results in contraction of muscles below the lesion. Initially the ES was conducted in an individual with a partial loss of sensation and a complete loss of motor control. This participant was able to voluntarily control movement in his legs while his spinal cord was being stimulated more than two years after his injury. This finding led the investigators to propose that the persisting sensory nerve connections played an integral role in performing voluntary muscle activity while being stimulated. This surprising finding led researchers to continue an on-going investigation into the effects of standing and step training with ES in individuals with chronic spinal cord injury.
In this study, researchers at the University of Louisville worked with four men who averaged 27 years of age. Each participant had complete loss of motor function below their level of lesion and sustained their injury more than two years before the start of the experiment. The investigators employed standing (using a standing frame) and step training (using body-weight support and manual movement of the lower limbs) and ES, which involves an implanted device in the lower spinal cord that sends an electric current along the nerves to target muscles with the aim of eliciting a response in different muscles. From the combination of laboratory standing and step training with ES, and home-based training with ES, all four participants were able to voluntarily activate muscles in their legs. The researchers did a series of experiments to determine whether the movements in the legs had resulted only from the electrical current or whether the participants could control the timing and strength of the movement. In most cases, the participants appeared to have the ability to voluntarily control the movements being performed.
Most Important Finding:
Following training and implantation with the epidural stimulation unit, all four participants performed voluntary leg movements on command while receiving electrical stimulation to the spinal cord. They were all able to activate specific muscle groups and regulate the amount of activation while receiving stimulation. Furthermore, over the course of the experiment, participants improved their control over voluntary leg movements with ES.
Additionally, after implantation but before repetitive training, all three tested participants were able to voluntarily execute movements in their legs with ES. This observation suggests that previously inactive neural connections may have persisted after the injury to the spinal cord. The authors suggest that the stimulation allows the spinal cord to ‘wake up.’
In a review of their findings, the authors proposed that the loss of voluntary control in individuals with complete paralysis might be caused by both the injury and by a change in the sensitivity of the spinal circuitry to receive and send the activation signal to the target muscles.
Things to Consider:
The authors acknowledge that the lack of user-friendly software limits the translation of laboratory improvements to everyday activities. However, the participants in this study are currently enjoying greater strength and stability, and less fatigue while using ES during exercise. One participant stated in an interview that he experienced benefits relating to secondary side effects of spinal cord injury, including improvements in bowel, bladder, and sexual function; however, future research is needed to explore these areas. Overall, these findings underscore the importance of resolving the uncertainty surrounding the diagnosis of complete paralysis with no possible recovery. Nevertheless, it is important to keep in mind that clinicians still have to provide a prognosis based on the majority of the knowledge to date.
What does this mean for people living with SCI?
The investigators state that although the exact mechanisms behind their results are uncertain, their findings do warrant the reconsideration of the definition and the way we think about complete spinal cord injuries. They also suggest that their methods could be used to develop effective intervention strategies to potentially improve recovery outcomes for people with chronic complete paralysis of the legs.
Want to learn more?
Find the BBC News report of the study here.