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The Journal of Neuroscience, January 26, 2005, 25(4):889-895; doi:10.1523/JNEUROSCI.4534-04.2005
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Behavioral/Systems/Cognitive
Differential Effects of Cerebellar Inactivation on Eyeblink Conditioned Excitation and Inhibition
John H. Freeman, Jr,
Hunter E. Halverson, and
Amy Poremba
Department of Psychology, University of Iowa, Iowa City, Iowa 52242
The neural mechanisms underlying excitatory and inhibitory eyeblink conditioning were compared using muscimol inactivation of the cerebellum. In experiment 1, rats were given saline or muscimol infusions into the anterior interpositus nucleus ipsilateral to the conditioned eye before each of four daily excitatory conditioning sessions. Postinfusion testing continued for four more excitatory conditioning sessions. All rats were given a final test session after muscimol infusions. The muscimol infusions inactivated the cerebellar nuclei, lateral anterior lobe, crus I, rostral crus II, and lobule HVI ipsilateral to the conditioned eye. Acquisition of excitatory conditioning was completely prevented by muscimol inactivation. In experiment 2, there were four experimental phases. Phase 1 consisted of excitatory conditioning. In phase 2, rats were given saline or muscimol infusions before conditioned inhibition training. Phase 3 consisted of continued conditioned inhibition training with no drug infusions. In phase 4, all rats received a retardation test in which the inhibitory stimulus was paired with the unconditioned stimulus. Muscimol infusions blocked the expression of conditioned responses during phase 2. However, robust conditioned inhibition was evident in phases 3 and 4. The findings indicate that conditioned excitation and inhibition depend on different mechanisms.
Key words: cerebellum; interpositus; learning; conditioning; eyeblink; muscimol
Received June 11, 2004;
revised November 4, 2004;
accepted December 7, 2004.
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