Duration of exposure to a novel environment affects retention in aging mice

Abstract

Aging mice were previously found not to retain information acquired in a single exposure to a novel environment as well as young mice. In an attempt to eliminate this difference, mice were given repeated daily 3-min exposures to a shuttlebox, and daily changes in exploratory activity reflected their retention of prior exposures. Activity levels progressively declined over days in all age groups (2, 12, and 24 months). However, activity in young mice fell to a lower level than that of the older mice, indicating that brief but repetitive learning sessions did not eliminate the age differences. Increasing each exposure session to 12 min eliminated the age differences in retention when the whole test session was examined. These data suggest that older mice may require more time to acquire the same amount of information as young mice. However, analysis of minute-by-minute acitivity over days indicated that older mice had forgotten their prior exposure at the first minute of each new session, but over the course of the next few minutes remembered their previous experience as well as young animals. Therefore, older mice also appear to be subject to retrieval failures even after they have received prolonged training sessions.