The cerebellum in maintenance of a motor skill: a hierarchy of brain and spinal cord plasticity underlies H-reflex conditioning.
Operant conditioning of the H-reflex, the electrical analog of the spinal stretch reflex, is a simple model of skill acquisition and involves plasticity in the spinal cord. Previous work showed that the cerebellum is essential for down-conditioning the H-reflex. This study asks whether the cerebellum is also essential for maintaining down-conditioning. After rats decreased the soleus H-reflex over 50 d in response to the down-conditioning protocol, the cerebellar output nuclei dentate and interpositus (DIN) were ablated, and down-conditioning continued for 50-100 more days. In naive (i.e., unconditioned) rats, DIN ablation itself has no significant long-term effect on H-reflex size. During down-conditioning prior to DIN ablation, eight Sprague-Dawley rats decreased the H-reflex to 57% (+/-4 SEM) of control. It rose after ablation, stabilizing within 2 d at about 75% and remaining there until approximately 40 d after ablation. It then rose to approximately 130%, where it remained through the end of study 100 d after ablation. Thus, DIN ablation in down-conditioned rats caused an immediate increase and a delayed increase in the H-reflex. The final result was an H-reflex significantly larger than that prior to down-conditioning. Combined with previous work, these remarkable results suggest that the spinal cord plasticity directly responsible for down-conditioning, which survives only 5-10 d on its own, is maintained by supraspinal plasticity that survives approximately 40 d after loss of cerebellar output. Thus, H-reflex conditioning seems to depend on a hierarchy of brain and spinal cord plasticity to which the cerebellum makes an essential contribution.
Wolpaw
Jonathan R
JR
Laboratory of Nervous System Disorders Wadsworth Center, New York State Department of Health and State University of New York at Albany, Albany, New York 12201-0509, USA. wolpaw@wadsworth.org
Chen
Xiang Yang
XY
D000818:Animals; D001245:Association Learning / Q000502:physiology; D001921:Brain / Q000166:cytology / Q000502:physiology; D002529:Cerebellar Nuclei / Q000166:cytology / Q000502:physiology; D002531:Cerebellum / Q000166:cytology / Q000502:physiology*; D003214:Conditioning, Classical / Q000502:physiology*; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D008297:Male; D009048:Motor Skills / Q000502:physiology*; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology