IMPACT OF AGE ON THE HIPPOCAMPUS-PREFRONTAL CIRCUIT IN SPATIAL WORKING MEMORY

Abstract

The hippocampus and prefrontal cortex are two brain regions that are critically important for executing cognitive processes involved in learning and memory. While these brain regions are known to be individually affected by age-related changes, the impact of aging on the hippocampal-prefrontal circuit remains unknown. For this study we used male Fischer 344 rats of two groups; young (8 months) and aged (22 months). These rats underwent a behavioral battery of cognitive tasks that tested hippocampus and prefrontal cortex function. They were trained on the spatial version of the Morris watermaze to test hippocampus function. Analysis of performance on this task shows that while both young and old rats show improvements in spatial learning across all four testing days, old rats show significantly worse performance on each day compared to young rats. Additionally, they were tested on the W-Maze spatial alternation task which looks at integrated hippocampus-prefrontal cortex function. This task consists of an inbound component testing spatial memory and an outbound component testing spatial working memory. For this task rats were yoked together across age groups and were then surgically implanted with dual-bundle hyperdrives targeting the ventral hippocampus and the medial prefrontal cortex. Analysis of behavioral results reveal that old rats learn the inbound component of the W-Maze task significantly slower than do young rats, and make significantly more errors on the outbound component of the W-Maze task. These results suggest that hippocampus-prefrontal cortex interactions degrade with age, and continued electrophysiological experiments on the spatial alternation task plan to investigate this. Understanding this mechanism may be important in understanding age-related cognitive decline.