To examine the effect of dietary restriction on spatial cognition, rats were divided into four groups (free feeding, 80%, 60%, or 40% of free feeding), and tested with Morris water maze place task throughout their lives. The escape platform was fixed at the first several sessions, then at the 9 months and thereafter, the platform was transferred to new location at every new session. Performance was not significantly different among groups when the subjects were at younger ages. However, at 9 months and thereafter, the 40% feeding group performed poorer than the other groups, and a quadratic relationship between performance and dietary restriction intensity was recognized. The optimal restriction intensities for the best spatial performance calculated from the quadratic equation were 98.3%, 88.9%, and 84.1 of free feeding at 9, 12, and 19 months old, respectively, suggesting that the stronger dietary restriction is desirable for better performance as aging proceeds.

Key words: long-term dietary restriction, aging, spatial cognition, Morris water maze, rats