Aging is known to impair the formation of episodic memory, a process dependent upon the integrity of the hippocampal region.  To investigate this issue, hippocampal place cells were recorded from middle-aged and old F-344 male rats while running on a ‘figure-8’ track.  The top and bottom arcs of the track were removed, converting it into a plus maze, and the animals were required to conduct a working memory task.  Following this change-in-task, the arcs were replaced and the animals again ran the ‘figure-8’ task.
    Analysis of place fields across the recording session demonstrated that both the middle-aged and old rats had reliable representations of the ‘figure-8’ task.  A comparison of the place fields between different behavioral tasks (‘figure-8’ and plus maze) demonstrated a change in the hippocampal representation of the environment in both age groups, despite the fact that the animals remained on the maze throughout the recording session.  Notably, place cells in old animals were less affected by the change-in-task than were those from middle-aged animals.
    The results suggest hippocampal neurons reflect significant behavioral events within a given environment.  Furthermore, the data indicate that age-related episodic memory deficits may result from decreased sensitivity of the hippocampal network to respond to meaningful changes in the environment.