Cognitive behavior was assessed in a test specific for spatial memory, according to a longitudinal experimental model, in populations of 12-, 24- and 30-month-old rats which were fed ad lib either a standard (ST) or a hypocaloric (HY) diet, that had been shown to reduce age-related pathologies and to increase survival. Already at 12 months of age, some cognitive deficits were observed in ST but not in HY rats. When retested 12 and 18 months later, the animals performed better at the beginning of the test than when tested for the first time, indicating that some aspects of previous experience lead to a preservation of spatial memory. Deficits which had been previously observed in 2-year-old groups in a cross-sectional experimental model were not evident this time. Some of the differences between the two diet groups observed 12 months before disappeared. When testing was repeated for the third time at 30 months of age, ST fed rats presented very marked deficits in learning and in memory, which were not seen in the HY group. It thus appears that a dietary regimen in which part of the calorie-rich components, such as lipids and carbohydrates, are replaced with vegetable fibers, retards some of the age-related deteriorations of brain functions.