Apps Richard, Lee Stephen
Department of Physiology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
J Physiol. 2002 May 15;541(Pt 1):301-17. doi: 10.1113/jphysiol.2002.016717.
A forelimb-withdrawal classical conditioning paradigm was used in awake cats (n = 4) to investigate changes in transmission in climbing fibre (CF) pathways during motor learning. The conditioned stimulus was an auditory tone, while the unconditioned stimulus was a low-intensity, single or double (0.1 ms) electrical pulse applied to the ipsilateral superficial radial nerve. Microwires chronically implanted into the paravermal cerebellar cortex (lobule V) were used to record the CF field potentials evoked by nerve stimulation, and fields at 22 recording sites (9 C1, 7 C2 and 6 C3 zone sites) were monitored during the complete sequence of at least one training run (i.e. over a period of about 2-3 weeks of conditioning). At 19 sites (86 %) conditioning led to a significant reduction in mean size of field. Similar reductions occurred at four sites studied over two successive training runs. At 10 sites (45 %) there was a statistically significant increase prior to the reduction. The three sites that failed to exhibit a significant reduction were all located in the C1 zone. Controls showed that the changes in CF transmission were dependent on the animal being conditioned. The mean size of CF field for trials in which a conditioned EMG response was present (in either the cleidobrachialis or biceps muscle) was not significantly different from the mean size for trials in which a conditioned response was absent. Similarly, on a trial-by-trial basis, CF pathway excitability was not correlated with the conditioned EMG activity in the flexor muscles under study. Overall, the results demonstrate that (1) the capacity of spino-olivocerebellar pathways (SOCPs) to forward information to the cerebellar cortex can be altered by recent experience, (2) establishment of a conditioned forelimb flexor reflex to a tone reduces SOCP excitability at most but not all sites within a forelimb-related region of the cerebellar cortex, (3) the extent of reductions differ at different sites and some are preceded by transient increases, and (4) the changes in transmission may not be related to the conditioned movement. The implications of these findings for some key theories of cerebellar cortical function are discussed.
在清醒猫（n = 4）中采用前肢撤回经典条件反射范式，以研究运动学习过程中攀爬纤维（CF）通路传递的变化。条件刺激是一个听觉音调，而无条件刺激是施加于同侧桡浅神经的低强度单脉冲或双脉冲（0.1毫秒）电刺激。长期植入小脑蚓旁皮质（小叶V）的微丝用于记录神经刺激诱发的CF场电位，并且在至少一次训练过程的完整序列中（即大约2 - 3周的条件反射期间）监测22个记录位点（9个C1、7个C2和6个C3区位点）的场电位。在19个位点（86%），条件反射导致场电位平均大小显著降低。在连续两次训练过程中研究的4个位点也出现了类似的降低。在10个位点（45%），在降低之前有统计学上显著的增加。未表现出显著降低的3个位点均位于C1区。对照表明CF传递的变化依赖于动物接受条件反射。存在条件性肌电图反应（在锁骨肱肌或二头肌中）的试验中CF场电位的平均大小与不存在条件性反应的试验中的平均大小无显著差异。同样，在逐个试验的基础上，CF通路兴奋性与所研究的屈肌中的条件性肌电图活动不相关。总体而言，结果表明：（1）脊髓 - 橄榄 - 小脑通路（SOCPs）向小脑皮质传递信息的能力可因近期经历而改变；（2）建立对音调的条件性前肢屈肌反射最多可降低但并非小脑皮质前肢相关区域内的所有位点的SOCP兴奋性；（3）不同位点降低的程度不同，有些位点在降低之前有短暂增加；（4）传递的变化可能与条件性运动无关。讨论了这些发现对小脑皮质功能一些关键理论的意义。
