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Voluntary Locomotion: New Findings in Spinal Cord Injury Therapy
Previously, we discussed the possible impact of anxiety levels on the development and progression of cancer. This week, we look into a study that hints at another side of this phenomenon: the potential power of will and determination, a concept utilized as part of a large study examining the plasticity of neuronal systems after partial spinal cord injury. Anecdotal evidence exists for the positive effect of determination and proper therapy in the partial recovery from central nervous system injury. Well-known gains in function were made by Christopher Reeve, college football player Chris Norton, and even Kevin Pearce, who recovered from a traumatic brain injury suffered in 2009.
In the recent study by van den Brand et al., food reinforcement was used alongside various therapy techniques to treat rats with paralyzed lower limbs, helping them regain voluntary control of hindlimb movement. While the rats used in the study had incomplete spinal cord injuries (cords were not completely transected), their injuries were severe and resulted in hindlimb paralysis.
The authors designed a multi-system neuroprosthetic training program consisting of 3 essential features including: electrical stimulation of the spinal cord over lumbar and sacral segments, training on a treadmill with a harness, and the spinal administration of serotonin and dopamine receptor agonists. This litany of treatment was designed to assist in the reorganization of spared neuronal systems through mechanisms dependent on usage. At first, this combination of therapies promoted coordinated involuntary stepping on a moving treadmill.
After treadmill stepping was achieved, the authors sought to achieve recovery of movements that require input from the brain: voluntary active use of the paralyzed hindlimbs. For this step, the rats continued to receive electrical and chemical spinal cord stimulation. A food reinforcer, such as chocolate or cheese, was set up as the target and focus to help stimulate active rat participation. Rats were gradually encouraged to move over the ground, and eventually over obstacles, aiming to enhance supraspinal contribution. All rats that received these treatments achieved restored voluntary locomotion in their hindlimbs. Each rat also showed remodeling of supraspinal and intraspinal neuronal projections, including in the motor cortex, and new pathways formed connecting the spinal cord to the brain. The over ground training was the key to this research: rats that were trained only to move on the treadmill did not regain connections between the brain and spinal cord and did not achieve voluntary locomotion.
While many factors were involved, the presentation of food reinforcement was an important part of the recovery of voluntary movement in these rats. The added motivation from the food reinforcer assisted in the development of new neuronal connections and the ability to voluntarily move hindlimbs across the ground. Among the many exciting findings from this study, this raises some interesting questions. How important is the presence of a clear goal in the production of movement? How are conscious motivation and voluntary movement connected and how can this connection be further utilized to assist recovery from injury?
van den Brand R, Heutschi J, Barraud Q, DiGiovanna J, Bartholdi K, Huerlimann M, Friedli L, Vollenweider I, Moraud EM, Duis S, Dominici N, Micera S, Musienko P, Courtine G. (2012). Restoring voluntary control of locomotion after paralyzing spinal cord injury. Science. Jun 1;336(6085):1182-5.