title: An investigation of the role of the hippocampus and the amygdala in the encoding of a serial pattern: Effects of a long inter-element interval.
abstract: Previous research has provided convincing evidence that rats can learn to anticipate each element of a stimulus series consisting of differing reinforcement quantities. The present experiment examined the effects of electrolytic lesions of the hippocampus, amygdala, or combined hippocampal and amygdala lesions on the acquisition of a 14-7-3-0 monotonic pattern with a 5 min inter-element interval. Anticipation was operationally defined as faster running on 14- than on 7-pellet elements, 7- than on 3-pellet elements, and 3- than 0-pellet elements. Male Sprague-Dawley rats (sham and lesioned) received two trials a day for 30 days on the 14-7-3-0 pattern of food pellets. Anticipatory tracking developed rapidly in the control animals and not until the end of training in the hippocampus + amygdala-lesioned rats, while the rate of acquisition in the single lesion groups was intermediate between the two. The results are discussed in terms of temporal and working memory processes. Mediation of the temporal and affective attributes of memory are considered for each structure. The present experiment provided additional evidence for a hippocampal role in maintenance of a temporal record of the elements of the series, thus providing the rat with the ability to track which stimulus elements have been presented and to anticipate future elements. Finally, via a role in processing the affective and reinforcing properties of the task, the amygdala appears to play a role in mnemonic processes.
authors.affiliation: Department of Psychology, Georgia College, Milledgeville, Georgia GA 31061-0490, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Compton