A COMPARISON OF TEMPORAL DECAY IN-PLACE MEMORY TASKS IN RATS (RATTUS-NORVEGICUS) WITH LESIONS AFFECTING THALAMUS, FRONTAL-CORTEX, OR THE HIPPOCAMPAL SYSTEM

Three experiments compared the effects of lesioning areas of thalamus, cortex, and the hippocampal system on delayed matching (DMTS) and non matching (DNMTS) to sample. Temporal decay was measured by comparing p erformances at different retention intervals (Rls) for rats trained to stability. Lesions of the lateral-internal medullary lamina site in t halamus and the medial wall area in frontal cortex produced impairment s that were significantly greater than for lesions of the mediodorsal nucleus in thalamus, the fornix, or the dorsal hippocampus. The effect s of lesions on temporal decay differed depending on how RIs were mani pulated. When Rls were manipulated within training sessions, the DMTS and DNMTS impairments were delay independent (i.e., none of the lesion s increased the rate of temporal decay). When RIs were manipulated bet ween sessions, thalamic lesions were associated with an increase in th e rate of temporal decay of DNMTS.