Submitted on May 20, 2007
Accepted on June 24, 2007
Enhancement of arm and leg locomotor coupling with augmented cutaneous feedback from the hand
E. Paul Zehr1*, Marc Klimstra2, Katie Dragert2, Yasaman Barzi3, Mark G. Bowden4, Bahar Javan3, and Chetan Phadke5
1 Rehabilitation Neuroscience Laboratory, University of Victoria, Faculty of Education, Victoria, V8W 3P1, Canada; Centre for Biomedical Research, University of Victoria, Victoria, Canada; Human Discovery Science, International Collaboration on Repair Discoveries, Vancouver, Canada
2 Rehabilitation Neuroscience Laboratory, University of Victoria, Victoria, Canada
3 Rehabilitation Neuroscience Laboratory, University of Victoria, Faculty of Education, Victoria, V8W 3P1, Canada
4 Brain Rehabilitation Research Center, University of Florida, Gainesville, Florida, United States
5 Departments of Physical Therapy and Neuroscience, University of Florida, Gainesville, Florida, United States
* To whom correspondence should be addressed. E-mail: pzehr{at}uvic.ca.
Cutaneous feedback from the hand could assist with coordination between the arms and legs during locomotion. Previously we used a reduced walking model of combined arm and leg (ARM&LEG) cycling to examine the separate effects of rhythmic arm (ARM) and leg (LEG) movement. Here we use this same paradigm to test the modulation H-reflexes with and without interlimb cutaneous conditioning evoked by stimulating a nerve innervating the hand (superficial radial, SR). It was hypothesized that both ARM and LEG would contribute significantly to suppression of H-reflex amplitude during ARM&LEG. We also predicted a conservation of interlimb cutaneous conditioning during movement and an interaction between arm and leg rhythmic movement control. Subjects were seated in a recumbent ARM&LEG cycle ergometer and maintained a low-level soleus contraction for all tasks. H-reflex amplitude was facilitated by cutaneous conditioning evoked by stimulation of the SR nerve. H-reflex amplitudes were taken from recruitment curves and included modulation of 50% Hmax and Hmax. The suppressive effect of ARM was less than that for LEG and ARM&LEG, while suppression during LEG and ARM&LEG were generally equivalent. For H-reflexes conditioned by cutaneous input, amplitudes during ARM&LEG instead were in between those for ARM and LEG modulation. Multiple regression analysis revealed a significant contribution for ARM only in trials when SR stimulation was used to condition H-reflex amplitudes. We suggest that there is a measurable interaction between neural activity regulating arm and leg movement during locomotion that is specifically enhanced when cutaneous input from the hand is present.
