@article {3109,
	title = {Acquisition of a simple motor skill: task-dependent adaptation plus long-term change in the human soleus H-reflex.},
	journal = {The Journal of neuroscience : the official journal of the Society for Neuroscience},
	volume = {29},
	year = {2009},
	month = {05/2009},
	pages = {5784{\textendash}5792},
	abstract = {Activity-dependent plasticity occurs throughout the CNS. However, investigations of skill acquisition usually focus on cortex. To expand the focus, we analyzed in humans the development of operantly conditioned H-reflex change, a simple motor skill that develops gradually and involves plasticity in both the brain and the spinal cord. Each person completed 6 baseline and 24 conditioning sessions over 10 weeks. In each conditioning session, the soleus H-reflex was measured while the subject was or was not asked to increase (HRup subjects) or decrease (HRdown subjects) it. When the subject was asked to change H-reflex size, immediate visual feedback indicated whether a size criterion had been satisfied. Over the 24 conditioning sessions, H-reflex size gradually increased in six of eight HRup subjects and decreased in eight of nine HRdown subjects, resulting in final sizes of 140 +/- 12 and 69 +/- 6\% of baseline size, respectively. The final H-reflex change was the sum of within-session (i.e., task-dependent) adaptation and across-session (i.e., long-term) change. Task-dependent adaptation appeared within four to six sessions and persisted thereafter, averaging +13\% in HRup subjects and -15\% in HRdown subjects. In contrast, long-term change began after 10 sessions and increased gradually thereafter, reaching +27\% in HRup subjects and -16\% in HRdown subjects. Thus, the acquisition of H-reflex conditioning consists of two phenomena, task-dependent adaptation and long-term change, that together constitute the new motor skill. In combination with previous data, this new finding further elucidates the interaction of plasticity in brain and spinal cord that underlies the acquisition and maintenance of motor skills.},
	keywords = {H-Reflex, motor learning, motor skill, operant conditioning, plasticity, Spinal Cord},
	issn = {1529-2401},
	doi = {10.1523/JNEUROSCI.4326-08.2009},
	url = {http://www.ncbi.nlm.nih.gov/pubmed/19420246},
	author = {Thompson, Aiko K. and Xiang Yang Chen and Jonathan Wolpaw}
}
@article {3161,
	title = {Motor unit properties after operant conditioning of rat H-reflex.},
	journal = {Experimental brain research. Experimentelle Hirnforschung. Exp{\'e}rimentation c{\'e}r{\'e}brale},
	volume = {140},
	year = {2001},
	month = {10/2001},
	pages = {382{\textendash}386},
	abstract = {Operant conditioning of the H-reflex produces plasticity at several sites in the spinal cord, including the motoneuron. This study assessed whether this spinal cord plasticity is accompanied by changes in motor unit contractile properties. Thirty-one adult male Sprague-Dawley rats implanted for chronic recording of triceps surae electromyographic activity and H-reflex elicitation were exposed for at least 40 days to HRup or HRdown training, in which reward occurred when the H-reflex was greater than (12 HRup rats) or less than (12 HRdown rats) a criterion value, or continued under the control mode in which the H-reflex was simply measured (7 HRcon rats). At the end of H-reflex data collection, rats were anesthetized and the contractile properties of 797 single triceps surae motor units activated by intraaxonal (or intramyelin) current injection were determined. Motor units were classified as S, FR, Fint, or FF on the basis of sag and fatigue properties. Maximum tetanic force and twitch contraction time were also measured. HRdown rats exhibited a significant increase in the fatigue index of fast-twitch motor units. This resulted in a significant decrease in the percentage of Fint motor units and a significant increase in that of FR motor units. HRup conditioning had no effect on fatigue index. Neither HRup nor HRdown conditioning affected maximum tetanic force or twitch contraction time. These data are consistent with the hypothesis that conditioning mode-specific change in motoneuron firing patterns causes activity-dependent change in muscle properties.},
	keywords = {H-Reflex, motor unit type, operant conditioning, plasticity, triceps surae},
	issn = {0014-4819},
	doi = {10.1007/s002210100830},
	url = {http://www.ncbi.nlm.nih.gov/pubmed/11681314},
	author = {Jonathan S. Carp and Xiang Yang Chen and Sheikh, H. and Jonathan Wolpaw}
}
@article {3240,
	title = {Operant conditioning of H-reflex increase in spinal cord{\textendash}injured rats.},
	journal = {Journal of neurotrauma},
	volume = {16},
	year = {1999},
	month = {02/1999},
	pages = {175{\textendash}186},
	abstract = {Operant conditioning of the spinal stretch reflex or its electrical analog, the H-reflex, is a new model for exploring the mechanisms of long-term supraspinal control over spinal cord function. Primates and rats can gradually increase (HRup conditioning mode) or decrease (HRdown conditioning mode) the H-reflex when reward is based on H-reflex amplitude. An earlier study indicated that HRdown conditioning of the soleus H-reflex in rats is impaired following contusion injury to thoracic spinal cord. The extent of impairment was correlated with the percent of white matter lost at the injury site. The present study investigated the effects of spinal cord injury on HRup conditioning. Soleus H-reflexes were elicited and recorded with chronically implanted electrodes from 14 rats that had been subjected to calibrated contusion injuries to the spinal cord at T8. At the lesion epicenter, 12-39\% of the white matter remained. After control-mode data were collected, each rat was exposed to the HRup conditioning mode for 50 days. Final H-reflex amplitudes after HRup conditioning averaged 112\% (+/-22\% SD) of control. This value was significantly smaller than that for 13 normal rats exposed to HRup conditioning, in which final amplitude averaged 153\% (+/-51\%) SD of control. As previously reported for HRdown conditioning after spinal cord injury, success was inversely correlated with the severity of the injury as assessed by white matter preservation and by time to return of bladder function. HRup and HRdown conditioning are similarly sensitive to injury. These results further demonstrate that H-reflex conditioning is a sensitive measure of the long-term effects of injury on supraspinal control over spinal cord functions and could prove a valuable measure of therapeutic efficacy.},
	keywords = {H-Reflex, operant conditioning, plasticity, rat, soleus muscle, spinal cord injury},
	issn = {0897-7151},
	url = {http://www.ncbi.nlm.nih.gov/pubmed/10098962},
	author = {Xiang Yang Chen and Jonathan Wolpaw and Jakeman, L. B. and Stokes, B. T.}
}
@article {3250,
	title = {Operant conditioning of H-reflex in spinal cord-injured rats.},
	journal = {Journal of neurotrauma},
	volume = {13},
	year = {1996},
	month = {12/1996},
	pages = {755{\textendash}766},
	abstract = {Operant conditioning of the spinal stretch reflex or its electrical analog, the H-reflex, is a new model for exploring the mechanisms of supraspinal control over spinal cord function. Both rats and primates can gradually increase (HRup conditioning mode) or decrease (HRdown conditioning mode) soleus H-reflex magnitude when exposed to an operant conditioning task. This study used H-reflex operant conditioning to assess and modify spinal cord function after injury. Soleus H-reflexes were elicited and recorded with chronically implanted electrodes from rats that had been subjected to calibrated contusion injuries to the spinal cord at T8. From 18 to 140 days after injury, background EMG, M response amplitude, and initial H-reflex amplitude were not significantly different from those of normal rats. HRdown conditioning was successful in some, but not all, spinal cord-injured rats. The H-reflex decrease achieved by conditioning was inversely correlated with the severity of the injury as assessed histologically or by time to return of bladder function. It was not correlated with the length of time between injury and the beginning of conditioning. The results confirm the importance of descending control from supraspinal structures in mediating operantly conditioned change in H-reflex amplitude. In conjunction with recent human studies, they suggest that H-reflex conditioning could provide a sensitive new means for assessing spinal cord function after injury, and might also provide a method for initiating and guiding functional rehabilitation.},
	keywords = {H-Reflex, operant conditioning, plasticity, rat, soleus muscle, spinal cord injury},
	issn = {0897-7151},
	url = {http://www.ncbi.nlm.nih.gov/pubmed/9002061},
	author = {Xiang Yang Chen and Jonathan Wolpaw and Jakeman, L. B. and Stokes, B. T.}
}
@article {3253,
	title = {Reversal of H-reflex operant conditioning in the rat.},
	journal = {Experimental brain research. Experimentelle Hirnforschung. Exp{\'e}rimentation c{\'e}r{\'e}brale},
	volume = {112},
	year = {1996},
	month = {11/1996},
	pages = {58{\textendash}62},
	abstract = {In response to an operant conditioning task, rats can gradually increase or decrease soleus H-reflex amplitude without change in background electromyographic activity or M response amplitude. Both increase (under the HRup mode) and decrease (under the HRdown mode) develop over weeks. The present study investigated reversal of conditioned H-reflex change. Following collection of control data, rats were exposed to one mode (HRup or HRdown) for 50 days, and then exposed to the opposite mode for up to 72 days. Rats responded to each mode exposure with gradual, mode-appropriate change in H-reflex amplitude. This finding is consistent with other evidence that H-reflex conditioning depends on spinal cord plasticity. The effects of exposure to the HRup (or HRdown) mode were not affected by whether exposure followed previous exposure to the HRdown (or HRup) mode. In accord with recent studies suggesting that HRup and HRdown conditioning have different spinal mechanisms, these results suggest that reversal of H-reflex change is due primarily to the superimposition of additional plasticity rather than to decay of the plasticity responsible for the initial change.},
	keywords = {H-Reflex, operant conditioning, plasticity, rat, soleus muscle, Spinal Cord},
	issn = {0014-4819},
	doi = {10.1007/BF00227178},
	url = {http://www.ncbi.nlm.nih.gov/pubmed/8951407},
	author = {Xiang Yang Chen and Jonathan Wolpaw}
}
@article {3255,
	title = {Operantly conditioned plasticity and circadian rhythm in rat H-reflex are independent phenomena.},
	journal = {Neuroscience letters},
	volume = {195},
	year = {1995},
	month = {08/1995},
	pages = {109{\textendash}112},
	abstract = {Recent studies indicate that rats can increase or decrease H-reflex amplitude in response to an operant conditioning paradigm. In addition, rats also display a circadian rhythm in H-reflex amplitude. As part of the development of H-reflex conditioning in the rat as a new model for defining the plasticity underlying a simple form of learning, this study examined the relationship in the rat between operantly conditioned H-reflex change and the H-reflex circadian rhythm. When H-reflex amplitude increased or decreased in response to the operant conditioning program, its circadian rhythm showed no changes in phase and minimal change in amplitude. Furthermore, animals did not alter daily performance schedule so as to use the rhythm to increase reward probability. Thus, in the rat, H-reflex operant conditioning and the H-reflex circadian rhythm appear to be independent phenomena. The circadian rhythm should not be a significant complicating factor in studies of operantly conditioned H-reflex change.},
	keywords = {circadian rhythm, H-Reflex, Learning, Memory, operant conditioning, Rats},
	issn = {0304-3940},
	doi = {10.1016/0304-3940(95)11793-V},
	url = {http://www.ncbi.nlm.nih.gov/pubmed/7478262},
	author = {Xiang Yang Chen and Jonathan Wolpaw}
}
