02325nas a2200229   4500008004100000022001400041245009300055210006900148260001200217300001200229490000700241520165100248653001301899653001101912653002501923653001501948653001601963100002101979700002502000700002302025856004702048       1993                        eng d  a0014-481900aOperant conditioning of the primate H-reflex: factors affecting the magnitude of change.0 aOperant conditioning of the primate Hreflex factors affecting th  c12/1993  a31–390 v973 aPrimates 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)10aH-Reflex10amonkey10aoperant conditioning10aplasticity10aSpinal Cord1 aWolpaw, Jonathan1 aHerchenroder, P., A.1 aCarp, Jonathan, S.  uhttp://www.ncbi.nlm.nih.gov/pubmed/8131830