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The Journal of Neuroscience, July 20, 2005, 25(29):6898-6906; doi:10.1523/JNEUROSCI.1684-05.2005

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Development/Plasticity/Repair
The Interaction of a New Motor Skill and an Old One: H-Reflex Conditioning and Locomotion in Rats

Yi Chen,^1,2 Xiang Yang Chen,¹ Lyn B. Jakeman,² Gerwin Schalk,¹ Bradford T. Stokes,² and Jonathan R. Wolpaw¹

¹Laboratory of Nervous System Disorders, Wadsworth Center, New York State Department of Health and State University of New York, Albany, New York 12201, and ²Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio 43210

New and old motor skills can interfere with each other or interact in other ways. Because each skill entails a distributed pattern of activity-dependent plasticity, investigation of their interactions is facilitated by simple models. In a well characterized model of simple learning, rats and monkeys gradually change the size of the H-reflex, the electrical analog of the spinal stretch reflex. This study evaluates in normal rats the interactions of this new skill of H-reflex conditioning with the old well established skill of overground locomotion.

In rats in which the soleus H-reflex elicited in the conditioning protocol (i.e., the conditioning H-reflex) had been decreased by down-conditioning, the H-reflexes elicited during the stance and swing phases of locomotion (i.e., the locomotor H-reflexes) were also smaller. Similarly, in rats in which the conditioning H-reflex had been increased by up-conditioning, the locomotor H-reflexes were also larger.

Soleus H-reflex conditioning did not affect the duration, length, or right/left symmetry of the step cycle. However, the conditioned change in the stance H-reflex was positively correlated with change in the amplitude of the soleus locomotor burst, and the correlation was consistent with current estimates of the contribution of primary afferent input to the burst.

Although H-reflex conditioning and locomotion did not interfere with each other, H-reflex conditioning did affect how locomotion was produced: it changed soleus burst amplitude and may have induced compensatory changes in the activity of other muscles. These results illustrate and clarify the subtlety and complexity of skill interactions. They also suggest that H-reflex conditioning might be used to improve the abnormal locomotion produced by spinal cord injury or other disorders of supraspinal control.

Key words: H-reflex conditioning; spinal cord plasticity; motor control; learning; memory consolidation; locomotion; rehabilitation

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Received Feb 17, 2005; revised June 9, 2005; accepted June 10, 2005.

This article has been cited by other articles:

				X. Y. Chen, S. Pillai, Y. Chen, Y. Wang, L. Chen, J. S. Carp, and J. R. Wolpaw Spinal and Supraspinal Effects of Long-Term Stimulation of Sensorimotor Cortex in Rats J Neurophysiol, August 1, 2007; 98(2): 878 - 887. [Abstract] [Full Text] [PDF]

				A. W. English, Y. Chen, J. S. Carp, J. R. Wolpaw, and X. Y. Chen Recovery of Electromyographic Activity After Transection and Surgical Repair of the Rat Sciatic Nerve J Neurophysiol, February 1, 2007; 97(2): 1127 - 1134. [Abstract] [Full Text] [PDF]

				E. P. Zehr Training-induced adaptive plasticity in human somatosensory reflex pathways J Appl Physiol, December 1, 2006; 101(6): 1783 - 1794. [Abstract] [Full Text] [PDF]

				Y. Chen, X. Y. Chen, L. B. Jakeman, L. Chen, B. T. Stokes, and J. R. Wolpaw Operant Conditioning of H-Reflex Can Correct a Locomotor Abnormality after Spinal Cord Injury in Rats J. Neurosci., November 29, 2006; 26(48): 12537 - 12543. [Abstract] [Full Text] [PDF]

				X. Y. Chen, L. Chen, Y. Chen, and J. R. Wolpaw Operant Conditioning of Reciprocal Inhibition in Rat Soleus Muscle J Neurophysiol, October 1, 2006; 96(4): 2144 - 2150. [Abstract] [Full Text] [PDF]

				X. Y. Chen, J. S. Carp, L. Chen, and J. R. Wolpaw Sensorimotor Cortex Ablation Prevents H-Reflex Up-Conditioning and Causes a Paradoxical Response to Down-Conditioning in Rats J Neurophysiol, July 1, 2006; 96(1): 119 - 127. [Abstract] [Full Text] [PDF]

				J. R. Wolpaw and X. Y. Chen The cerebellum in maintenance of a motor skill: A hierarchy of brain and spinal cord plasticity underlies H-reflex conditioning. Learn. Mem., March 1, 2006; 13(2): 208 - 215. [Abstract] [Full Text] [PDF]

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