ABSTRACT
A number of correlational studies have implicated the hippocampus and related structures in classical conditioning of the nictitating membrane (NM) response in rabbits (for a review, see Thompson, Berger, Berry, & Hoehler, 1980). In their summary, Thompson et al. conclude:
In the learning paradigm we employ, the growth of the hippocampal unit response is completely predictive of subsequent behavioral learning. If the hippocampal response does not develop, the animal will not learn. If it develops rapidly, the animal will learn rapidly. If it develops slowly, the animal will learn slowly. Further, the temporal form of the hippocampal response predicts the temporal form of the behavioral response.
(p. 212) One test of this hypothesized hippocampal involvement in classical NM conditioning would be to assess the behavioral effects of disruption of hippocampal activity. Although hippocampal lesions have little effect upon initial acquisition (Schmaltz & Theios, 1972), Salafia and his colleagues (Salafia & Allan, 1980; Salafia, Romano, Tynan, & Host, 1977) have demonstrated severe disruption of NM conditioning after direct electrical stimulation of the hippocampus. Other treatments that affect hippocampal activity, such as septal lesions (Powell, Milligan, & Buchanan, 1976) and anticholinergic drugs (Moore, Goodell, & Solomon, 1976; Powell, 1979: Solomon & Gottfried, 1981), have been shown to retard acquisition of the NM response. Unfortunately, neural recordings have not typically been performed during or after such disruptive treatments, so the precise impact of, for example, septal lesions or anticholinergic drugs on hippocampal activity in the learning situation is not known. Rather than assuming that such treatments alter the hippocampus-learning relationships described by Thompson et al. (1980), it is important to conduct experiments that measure both neural and behavioral effects of manipulations that retard conditioning. This chapter is a summary of some experiments of that nature. Specifically, we tested correlations between neural activity and behavioral learning in (1) intact, undrugged animals displaying variations in conditioning rate, (2) animals with disruptive medial septal lesions, and (3) animals treated with Δ9-THC, a psychoactive component of marijuana with demonstrated effects on hippocampal activity (Cosroe, Jones, & Laird, 1976; Segal, 1978). In all experiments, recordings were taken of CA1 hippocampal EEG and multiple-unit activity as well as behavior.