Acquisition, maintenance, and therapeutic use of a simple motor skill

Abstract

Operant conditioning of the spinal stretch reflex (SSR) or its electrical analog, the H-reflex, is a valuable experimental paradigm for studying the acquisition and maintenance of a simple motor skill. The CNS substrate of this skill consists of brain and spinal cord plasticity that operates as a hierarchy—the learning experience induces plasticity in the brain that guides and maintains plasticity in the spinal cord. This is apparent in the two components of the skill acquisition: task-dependent adaptation, reflecting brain plasticity; and long-term change, reflecting gradual development of spinal plasticity. The inferior olive, cerebellum, sensorimotor cortex, and corticospinal tract (CST) are essential components of this hierarchy. The neuronal and synaptic mechanisms of the spinal plasticity are under study. Because acquisition of this skill changes the spinal cord, it can affect other skills, such as locomotion. Thus, it enables investigation of how the highly plastic spinal cord supports the acquisition and maintenance of a broad repertoire of motor skills throughout life. These studies have resulted in the negotiated equilibrium model of spinal cord function, which reconciles the spinal cord’s long-recognized reliability as the final common pathway for behaviors with its recently recognized ongoing plasticity. In accord with this model, appropriate H-reflex conditioning in a person with spasticity due to an incomplete spinal cord injury can trigger wider beneficial plasticity that markedly improves walking. H-reflex operant conditioning appears to provide a valuable new method for enhancing functional recovery in people with spinal cord injury and possibly other disorders as well.

Retraining Reflexes: Clinical Translation of Spinal Reflex Operant Conditioning

“…Furthermore, in rats with incomplete spinal cord injury, inappropriate conditioning (i.e., down-conditioning the soleus Hreflex to further weaken stance) did not further impair locomotion [39]. The absence of deleterious effects is likely to reflect appropriate compensatory plasticity; and it is in accord with the negotiated equilibrium model of spinal cord function [177,178,182]. Third, in a person with impaired motor function, appropriate reflex conditioning can trigger wider beneficial plasticity [41].…”

“…The reflex changes gradually over days and weeks due to plasticity in both the brain and the spinal cord. This plasticity appears to comprise a hierarchy in which the plasticity in the brain induces and maintains the plasticity in the spinal cord [43,175,176] (reviewed in [42,177,178]). Figure 2 illustrates the operant conditioning protocol for the human soleus H-reflex [33].…”

“…Ongoing investigations are exploring the combination of spinal reflex conditioning with other rehabilitation therapies, such as locomotor training [189]. Finally, scientific inquiries continue into the mechanisms of the plasticity in the brain and spinal cord that underlies spinal reflex conditioning (see [42,177,178] for review).…”

Motor Recovery After Stroke: From a Vespa Scooter Ride Over the Roman Sampietrini to Focal Muscle Vibration (fMV) Treatment. A 99mTc-HMPAO SPECT and Neurophysiological Case Study

“…In this regard, there is no agreement in the literature about the number of fMV sessions required for motor improvement to be very effective. Since the amount of the induced change grows gradually as conditioning trials continue over subsequent days and weeks ( 35 , 36 ) we decided to carry out a total of 12 fMV sessions (3 sessions per week for 4 consecutive weeks), thereby extending the classic one-week treatment (overall 3 sessions) ( 13 , 19 , 37 ).…”

Activity-dependent synaptic dynamics in motor circuits of the spinal cord

“…When considering ADSP in the ventral spinal cord networks that generate locomotor and postural commands, the term "activity" may lead to some confusion as it could refer to "movement" or "training" instead of the "rate of action potential firing" in presynaptic neurons. Several recent reviews have reported the numerous plastic changes (morphological changes, axonal sprouting, …etc) induced by motor activities as well as by motor task learning in the spinal motor networks under both physiological and pathophysiological conditions (see for examples [3][4][5]). However, although interacting functionally through overlapping elements, a distinction should be made between the overall impact of the neuronal activity generated during training or learning and the continuous and dynamic integration of firing rate that occurs in synaptic connections.…”