Plasticity in the Central Nervous System: Operant Conditioning of the Spinal Stretch Reflex

Studies in monkey models have demonstrated that spinal stretch reflexes (SSRs) can be conditioned to be smaller or larger. Results of H-reflex conditioning studies further support the concept that operant conditioning alters the anatomical and biophysical properties of targeted alpha motoneurons. Results from able-bodied human subjects are strikingly similar to results from monkey models. Conditioning paradigms appear successful in downtraining the SSR of spinal-cord-injured patients who present with some residual control of a hyperactive biceps brachii. The conditioning may also affect movement control of spinal-cord-injured patients. Initial attempts at conditioning hyperactive SSRs of stroke patients have been equivocal. The site of lesion probably influences whether a stroke patient can successfully condition the SSR.