Age-related differences in the anticipation of future rewards.

The present study examined the anticipation of future reward in 7-mo- and 26-mo-old Fischer 344/Brown Norway rats. Young and old rats were divided randomly and assigned into one of two conditions. In the Contrast Condition, subjects were given a water solution containing 2% sucrose for 3 min followed immediately by a water solution containing 32% sucrose for 3 min. In the No-Contrast Condition, subjects were given a water solution containing 2% sucrose for 3 min followed immediately by a water solution containing 2% sucrose for 3 min. Across 10 days of testing in the Contrast Condition, young rats showed significantly less intake of the less preferred 2% sucrose solution, whereas old rats showed increased intake of the 2% sucrose solution. Young rats showed a significant increase in intake of the preferred 32% sucrose solution compared to aged rats across the 10-day testing period with the exception of days 8-10 where intake did not differ between groups. In the No-Contrast Condition, there were no significant differences between young and old rats, with both groups consuming significantly more of the first 2% solution than the second 2% solution. Therefore, these data suggest that age-related changes may impair the ability to anticipate future rewards.