ENCODING OF A NONMONOTONIC SERIAL PATTERN - ROLE OF THE DORSAL HIPPOCAMPUS AND AMYGDALA

The present experiment examined the effects of lesions of the hippocam pus, amygdala, or combined hippocampal + amygdala lesions on the acqui sition of a presumably difficult serial pattern. Lesioned rats, sham-s urgical and nonsurgical control rats were trained in a runway to track one of a four-element series of Noyes food pellets consisting of 14-0 -3-7 pellets, respectively. Control rats were capable of tracking the elements of the series. Tracking developed in the amygdala-lesions gro up by the middle stages of training, but tracking did not develop in t he hippocampal-lesion group until the end of training and failed to de velop in the hippocampus + amygdala-lesion group. The results are disc ussed in terms of hippocampus and amygdala involvement in working memo ry processes. The role of each structure in processing the temporal an d affective attributes of the task is considered. Presumably, the hipp ocampus is necessary for tasks requiring the sequential coding of info rmation. The hippocampus appears to maintain a temporal record of the elements of the series providing the rat with the ability to track whi ch stimulus elements have been presented and which have not. In additi on, by processing the affective attributes of the task, the amygdala a ppears to mediate mnemonic processes.