Journal of Neuroscience, Vol 13, 1624-1635, Copyright © 1993 by Society for Neuroscience
Recoverable and nonrecoverable deficits in conditioned responses after cerebellar cortical lesions
JA Harvey, JP Welsh, CH Yeo and AG Romano
Department of Pharmacology, Medical College of Pennsylvania/EPPI, Philadelphia 19129.
This study reexamined the effects of unilateral damage to cerebellar
hemispheral lobule VI on the rabbit's conditioned nictitating membrane (NM)
response. Extensive unilateral removal of hemispheral lobule VI in 11
rabbits impaired ipsilateral conditioned responses as reflected by
reductions of 52% in mean frequency and 53% in mean amplitude during test
trials on the first postoperative session. The decreases in the amplitude
and frequency of conditioned responses were highly correlated (r = 0.82).
The frequency of conditioned responses recovered to control levels but
their amplitudes remained reduced such that the correlation between these
two measures of responding was no longer significant by the 12th
postoperative conditioning session. The decrease in the amplitude of
conditioned responses was not accompanied by changes in onset latency or
rise time. There was no significant impairment of conditioned responses in
surgical controls and animals with only partial damage to hemispheral
lobule VI. It was concluded that hemispheral lobule VI plays an important
role in the regulation of motor centers in the brainstem so as to
facilitate the initiation and optimum execution of the conditioned NM
reflex. This cortical regulation of the conditioned NM response may contain
learned elements; however, these cannot be resolved with lesion methods,
nor has their existence been proven in this or other lesion studies.
Nevertheless, the results of this study do demonstrate that the cerebellar
cortex cannot be considered as the single locus necessary for NM
conditioning.
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