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.
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
Jonathan R
JR
Wolpaw
Xiang Yang
XY
Chen
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