@article {3164, title = {Sag during unfused tetanic contractions in rat triceps surae motor units.}, journal = {Journal of neurophysiology}, volume = {81}, year = {1999}, month = {06/1999}, pages = {2647{\textendash}2661}, abstract = {Contractile properties and conduction velocity were studied in 202 single motor units of intact rat triceps surae muscles activated by intra-axonal (or intra-myelin) current injection in L5 or L6 ventral root to assess the factors that determine the expression of sag (i.e., decline in force after initial increase during unfused tetanic stimulation). Sag was consistently detected in motor units with unpotentiated twitch contraction times <20 ms. However, the range of frequencies at which sag was expressed varied among motor units such that there was no single interstimulus interval (ISI), with or without adjusting for twitch contraction time, at which sag could be detected reliably. Further analysis indicated that using the absence of sag as a criterion for identifying slow-twitch motor units requires testing with tetani at several different ISIs. In motor units with sag, the shape of the force profile varied with tetanic frequency and contractile properties. Simple sag force profiles (single maximum reached late in the tetanus followed by monotonic decay) tended to occur at shorter ISIs and were observed more frequently in fatigue-resistant motor units with long half-relaxation times and small twitch amplitudes. Complex sag profiles reached an initial maximum early in the tetanus, tended to occur at longer ISIs, and were more common in fatigue-sensitive motor units with long half-relaxation times and large twitch amplitudes. The differences in frequency dependence and force maximum location suggested that these phenomena represented discrete entities. Successive stimuli elicited near-linear increments in force during tetani in motor units that never exhibited sag. In motor units with at least one tetanus displaying sag, tetanic stimulation elicited large initial force increments followed by rapidly decreasing force increments. That the latter force envelope pattern occurred in these units even in tetani without sag suggested that the factors responsible for sag were expressed in the absence of overt sag. The time-to-peak force (TTP) of the individual contractions during a tetanus decreased in tetani with sag. Differences in the pattern of TTP change during a tetanus were consistent with the differences in force maximum location between tetani exhibiting simple and complex sag. Tetani from motor units that never exhibited sag did not display a net decrease in TTP during successive contractions. These data were consistent with the initial force decrement of sag resulting from a transient reduction in the duration of the contractile state.}, keywords = {Regression Analysis}, issn = {0022-3077}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10368385}, author = {Jonathan S. Carp and Herchenroder, P. A. and Xiang Yang Chen and Jonathan Wolpaw} } @article {3172, title = {Operant conditioning of the primate H-reflex: factors affecting the magnitude of change.}, journal = {Experimental brain research. Experimentelle Hirnforschung. Exp{\'e}rimentation c{\'e}r{\'e}brale}, volume = {97}, year = {1993}, month = {12/1993}, pages = {31{\textendash}39}, abstract = {Primates can gradually increase or decrease H-reflex amplitude in one leg when reward depends on that amplitude. The magnitude of change varies greatly from animal to animal. This study sought to define the factors that control this magnitude. It evaluated the influence of animal age, muscle size (absolute and relative), background electromyographic activity (EMG) level, M response amplitude, initial H-reflex amplitude, performance intensity, and behavior of the contralateral leg. Fifty-four animals (Macaca nemestrina) underwent operant conditioning of the triceps surae H-reflex in one leg (the trained leg). Twenty-eight were rewarded for larger H-reflexes (HRup animals), and 26 were rewarded for smaller H-reflexes (HRdown animals). In the HRup animals, H-reflex amplitude in the trained leg rose to an average final value of 177\% of its initial amplitude. Magnitude of increase varied widely across animals. Nine animals rose to 120-140\%, 11 to 160-240\%, three to 300\% or more, and five remained within 20\% of initial amplitude. In the HRdown animals, H-reflex amplitude in the trained leg decreased to an average of 69\% of initial amplitude. Magnitude of decrease varied widely. Five animals decreased to 20-40\%, seven to 40-60\%, six to 60-80\%, and eight remained within 20\% of initial amplitude. Animal age, as assessed by weight, markedly affected HRdown conditioning, but not HRup conditioning. Heavy HRdown animals (> or = 6 kg) were more successful than light HRdown animals (< 6 kg). Thirteen of 14 heavy animals and only five of 12 light animals decreased to less than 80\% of initial amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)}, keywords = {H-Reflex, monkey, operant conditioning, plasticity, Spinal Cord}, issn = {0014-4819}, doi = {10.1007/BF00228815}, url = {http://www.ncbi.nlm.nih.gov/pubmed/8131830}, author = {Jonathan Wolpaw and Herchenroder, P. A. and Jonathan S. Carp} } @article {3269, title = {Operant conditioning of H-reflex in freely moving monkeys.}, journal = {Journal of neuroscience methods}, volume = {31}, year = {1990}, month = {02/1990}, pages = {145{\textendash}152}, abstract = {The H-reflex, the electrical analog of the stretch reflex or tendon jerk, is the simplest behavior of the primate CNS. It is subserved by a wholly spinal two-neuron reflex arc. Recent studies show that this reflex can be increased or decreased by operant conditioning, and that such conditioning causes plastic changes in the spinal cord itself. Thus, H-reflex conditioning provides a powerful new model for investigating primate memory traces. The key feature of this model, the conditioning task, originally required animal restraint. This report describes a new tether-based design that allows H-reflex measurement and conditioning without restraint. This design integrates the conditioning task into the life of the freely moving animal.}, keywords = {conditioning, H-Reflex, Memory, plasticity, primate, spinal reflex, stretch reflex}, issn = {0165-0270}, doi = {10.1016/0165-0270(90)90159-D}, url = {http://www.ncbi.nlm.nih.gov/pubmed/2319815}, author = {Jonathan Wolpaw and Herchenroder, P. A.} }