MEMORY FOR SPATIAL LOCATION AS A FUNCTION OF TEMPORAL LAG IN RATS - ROLE OF HIPPOCAMPUS AND MEDIAL PREFRONTAL CORTEX

Rats with medial prefrontal cortex, hippocampus, or cortical control l esions were tested on an eight-arm radial maze task, in order to exami ne memory for the temporal order of spatial locations as a function of temporal lag. During the study phase of each trial, rats were allowed to visit each of eight arms once in an order that was randomly select ed for that trial. The test phase required the rats to choose which of two arms occurred earlier in the sequence of arms visited during the study phase. The arms selected as test arms varied according to tempor al lag (0-6) or the number of arms that occurred between the two test arms in the study phase. The control rats performed at chance at a tem poral lag of zero, but their performance was above chance for the rema ining lags, improving after the temporal lag exceeded zero. The hippoc ampal-lesioned rats showed a marked deficit, performing at chance for all lags, with some savings for those items occurring at the end of th e list. The medial prefrontal cortex-lesioned rats showed a less sever e deficit. The results of these data support the notion that both the hippocampus and the medial prefrontal cortex play significant roles in memory for the temporal order of spatial locations. (C) 1994 Academic Press, Inc.