Intraspinal Plasticity Associated With Locomotor Learning

Objectives We aim to determine whether the development of a motor memory in the human spinal cord circuitry (expressed as a down regulation of the monosynaptic soleus H reflex) after a brief period of learning of a locomotor skill, is intrinsically encoded at the spinal cord level or if it is determined by descending suprasegmental influences. The results of this study would be useful for designing new rehabilitation strategies based upon manipulation of peripheral inputs aimed at activating spinal cord circuitry for motor recovery independent of the higher centers. Study population Seventy (70) healthy volunteers (median age 21-65) will participate in the study. Design Subjects will complete one training session (using a recumbent cycle ergometer) and will be tested physiologically and behaviorally once before training and four times after training through 14 to 16 days. Outcome measures We will assess homosynaptic depression of the soleus H reflex (an expression of the excitability of the alpha-motorneuron pool), a phenomenon that is not susceptible to descending suprasegmental influences but depends on the history of information arriving to the alpha-motorneuron from the periphery. Amount of homosynaptic depression will be correlated with the behavioral learning assessed by improvement in control of stepping speed.