The effect of brachium conjunctivum transection on a conditioned limb response in the cat

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Seven cats were trained to perform a forelimb conditioned response to a paired tone conditioned stimulus (CS)/shock unconditioned stimulus (UCS). Brachium conjunctivum section ipsilateral to the trained limb was carried out following criterion conditioned response (CR) performance. Lesion sites were identified histologically and further confirmed by observation of cellular changes in the dentate and interpositus nuclei ipsilateral to the section. The brachium conjunctivum was found to have been sectioned in four of the seven subjects. Each of these animals demonstrated a total or near-total loss of the CR. Extended postoperative training resulted in no increase in CR performance levels. The unconditioned response (UCR) remained unaffected, as did limb placing, accuracy of striking at moving objects, grooming, running and walking. The results are discussed in the context of an earlier report by McCormick et al. [Bull Psychonom Soc 1981;18:103–5], in which section of the superior cerebellar peduncle was found to abolish a conditioned nictitating membrane response in the rabbit. Taken together, they support the contention of Lavond [Annu Rev Psychol 1993;44:317–42], Thompson [In: Sprague JM, Epstein AN, editors. Progress in Psychobiology and Physiological Psychology. New York: Academic Press 1983, pp. 167–96], Yeo et al. [Behav Brain Res 1984;13:261–66; Exp Brain Res 1985;60:87–98; Exp Brain Res 1985;60:99–113; Exp Brain Res 1992;88:623–38.] and others that the cerebellum represents a critical site for acquisition and retention of a conditioned memory trace.