Changing a Reflex to Improve Locomotion For Incomplete Spinal Cord Injury

With recent advances in acute care after spinal cord injury (SCI), which has resulted in more cases of incomplete SCI, and development of regeneration therapies, rehabilitation for functional recovery is becoming increasingly important for re-establishing an active, productive, fulfilling life in these individuals. In order to maximize functional recovery after SCI, it is extremely important to continue developing new therapeutic approaches beyond conventional rehabilitation techniques. The goal of this project is to investigate the therapeutic effects of changing a spinal reflex on impaired locomotion after chronic incomplete SCI. Successful completion of this project will open up a new therapeutic approach for treating individuals after SCI.

Thompson  Aiko, Project Coordinator Helen Hayes Hospitalcity: Menands: USA Grant 5R01NS069551-02 from National Institute Of Neurological Disorders And Stroke

Abstract: People with incomplete spinal cord injury (SCI) often have substantial disabilities, even after completing conventional therapy. Common motor abnormalities after SCI include spasticity and weak voluntary muscle control. Altered spinal reflex pathways contribute to these problems. In this population, exaggerated stretch reflex and abnormal reflex modification of the ankle extensors are frequently observed. Normally, spinal reflexes are modulated from standing to walking, and during walking reflexes are further modulated between different phases of the gait cycle. However, in individuals after SCI, modulation of the soleus H-reflex during walking is often absent or greatly diminished (i.e., the reflex amplitude remains high even in the early stance or swing phase, where the H-reflex is normally very small or absent). Spinal reflexes can be changed through operant conditioning. Previous work in rats and monkeys shows that successful operant conditioning of a spinal reflex changes not only the reflex pathway that is conditioned but also the activity of other spinal and supraspinal pathways. Therefore, it may be possible to guide central nervous system plasticity associated with learning to change the activity of a spinal reflex pathway such that movement disabilities can be ameliorated. The goal of this project is to investigate the impact of changing a spinal reflex on impaired locomotion after chronic incomplete SCI in people. In humans, reflex conditioning with a far smaller number of trials per day than those used in rats can produce a comparable amount of reflex change. Recent work in rats shows that soleus H-reflex operant conditioning changes soleus behavior during locomotion, and indicates that appropriate conditioning can improve locomotion after incomplete SCI. Based on these findings, this project will test two hypotheses. The first hypothesis is that, in subjects with spastic hyperreflexia due to chronic incomplete SCI, decreasing the soleus H-reflex by operant down-conditioning can improve locomotion. The second hypothesis is that, locomotion can be further improved by applying down-conditioning procedures during appropriate phases of locomotion, when the H-reflex should normally be absent. These hypotheses will be tested by applying down-conditioning of the soleus H-reflex in spastic subjects with incomplete SCI. The impact of conditioning on the locomotor EMG activity, reflex modulation during gait, gait kinematics, and walking speed will be assessed, before and after conditioning. We will also assess the persistence of these effects. We expect to find that successful H-reflex down-conditioning can improve locomotion recovery after incomplete SCI and that this improvement will persist. Successful completion of this project will facilitate development of spinal reflex operant conditioning as a new, therapeutic approach to improving motor function recovery for individuals after SCI. This new method should complement existing methods and augment restoration of useful function.  With recent advances in acute care after spinal cord injury (SCI), which has resulted in more cases of incomplete SCI, and development of regeneration therapies, rehabilitation for functional recovery is becoming increasingly important for re-establishing an active, productive, fulfilling life in these individuals. In order to maximize functional recovery after SCI, it is extremely important to continue developing new therapeutic approaches beyond conventional rehabilitation techniques. The goal of this project is to investigate the therapeutic effects of changing a spinal reflex on impaired locomotion after chronic incomplete SCI. Successful completion of this project will open up a new theraputic approach for treating individuals after SCI.

Reflex Control Could Improve Walking After Incomplete Spinal Injuries:

Operant conditioning protocols can modify the activity of specific spinal cord pathways and can thereby affect behaviors that use these pathways. To explore the therapeutic application of these protocols, we studied the impact of down-conditioning the soleus H-reflex in people with impaired locomotion caused by chronic incomplete spinal cord injury. After a baseline period in which soleus H-reflex size was measured and locomotion was assessed, subjects completed either 30 H-reflex down-conditioning sessions (DC subjects) or 30 sessions in which the H-reflex was simply measured [unconditioned (UC) subjects], and locomotion was reassessed. Over the 30 sessions, the soleus H-reflex decreased in two-thirds of the DC subjects (a success rate similar to that in normal subjects) and remained smaller several months later. In these subjects, locomotion became faster and more symmetrical, and the modulation of EMG activity across the step cycle increased bilaterally. Furthermore, beginning about halfway through the conditioning sessions, all of these subjects commented spontaneously that they were walking faster and farther in their daily lives, and several noted less clonus, easier stepping, and/or other improvements. The H-reflex did not decrease in the other DC subjects or in any of the UC subjects; and their locomotion did not improve. These results suggest that reflex-conditioning protocols can enhance recovery of function after incomplete spinal cord injuries and possibly in other disorders as well. Because they are able to target specific spinal pathways, these protocols could be designed to address each individual’s particular deficits, and might thereby complement other rehabilitation methods.

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