Amygdala, hippocampus and associative memory in rats

Male wistar rats received either electrolytic or sham lesions into the amygdala, hippocampus or amygdala plus hippocampus, or were assigned to an unoperated control group. In Experiment 1, all lesioned and control animals were tested for the ability to master an associative memory test in which recall was assessed over delays ranging between 10 and 180 s. The goal of Experiment 2 was to study the susceptibility to proactive interference following the above mentioned types of damage. The role of the amygdala and hippocampus in remembering stimulus-magnitude of reward associations was evaluated in Experiment 3. Lesions of the dorsal and ventral hippocampus had no effect on acquisition of the associative memory test, but disrupted the animals' performance in the task after 120 and 180 s delays. The same lesions increased the sensitivity to interference but did not impair the performance of several stimulus/magnitude of reward discriminations. By contrast, amygdala lesions impaired the acquisition of the associative memory paradigm and the animals' performance over the successive delays. Moreover, the animals with these lesions were not able to learn the stimulus/magnitude of reward discriminations, although they did not show an increased susceptibility to interference. Combined damage to the amygdala plus hippocampus severely disrupted the acquisition of the associative memory paradigm and the animals' performance over successive delays. The same damage increased the susceptibility of the animals to interference and impaired the performance in the stimulus-magnitude of reward discriminations.