Neuronal control of the classically conditioned nictitating membrane response in rabbit: a critical role for the dorsolateral pons.

Abstract

The dorsolateral pontine brain stem was investigated as a possible locus of neural elements mediating the classically conditioned rabbit nictitating membrane response. Lesioning, recording, and stimulating techniques were employed for this purpose. Radio-frequency lesions of the right dorsolateral pons severely impaired both acquisition and retention of the ipsilateral conditioned nictitating membrane response to visual, auditory, and tactile conditioned stimuli. Unconditioned responses were unaffected, and conditioning of the contralateral (left) eye was not impaired. These results suggested that disrupted conditioned responding was not due to sensory, motor, or attentional impairment. Thus, the neural control of the conditioned response is separate from that of the unconditioned reflex. Histological analyses indicated that the following structures were lesioned in disrupted animals and spared in the non-disrupted animals: locus subcoeruleus , the supratrigeminal region, brachium conjunctivum, and parabrachial nuclei. Low-impedance tungsten monopolar electrodes were chronically implanted into the pontine brain stem. Multiple-unit recording during classical conditioning revealed a conditioned increase in multiple-unit activity which developed and extinguished concurrently with the acquisition and extinction of the behavioral conditioned response. Pseudoconditioning and conditioned inhibition controls indicated that the