Spinal Cord Plasticity
Condition: Healthy
Study type: Observational

Summary: 
      This study will examine the role of the spinal cord in improving leg movements after physical
      training in healthy people. The results of this study may be helpful in developing new
      rehabilitation therapies for people with impaired leg function.

      Healthy volunteers between 21 and 65 years of age may be eligible for this study. Candidates
      will be screened with a brief medical history and physical examination.

      Participants will undergo EMG-H reflex measurement while pedaling on a stationary bicycle.
      For this test, the subject is given an electrical stimulation at the nerve at the back of the
      knee while pedaling on a stationary bicycle. The shock produces a jerky movement called the
      "H reflex." The muscular activity causing these reflexes is measured using electrodes (small
      metal disks) filled with a conductive gel and taped to the skin over the calf muscle. The
      nerve is stimulated at four different frequencies during the experiment. While cycling, pedal
      resistance changes, making it harder or easier to pedal.

      On study day 1, participants have EMG-H reflex measurement to determine baseline performance,
      then a training session to prepare for the actual test, and then a post-training test to
      measure performance again. The test is repeated on days 2, then between days 5 and 8, and
      again between days 11 and 14. The screening and first visit last 2 hours; the remaining test
      visits are 1 hour each. The bicycling time is only 15 minutes during training and 5 minutes
      at each test session.
    

Detailed description: 
      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.
    

Keywords: Spinal Reflexes; Locomotion; Motor Practice; Healthy Volunteer; HV