DEVELOPMENT OF SPATIAL MEMORY STRATEGIES IN SQUIRREL MONKEYS (COGNITIVE MAP).

Abstract

When different development rates for psychological processes such as those in spatial memory exist, they can be linked to relevant brain areas via their different developmental rates. The hippocampus and caudate nucleus have been implicated in allocentric and egocentric spatial behavior changes found in youth and old age. Variation in allocentric and egocentric behavior in squirrel monkeys due to age was examined using a quadruple T-maze and animals in three age groups: 0.3 - 4 year olds, (n = 12), 5 - 10 year olds (n=12) and 11 - 17 year olds (n = 12). Subjects were trained to go to one of three goals in the maze from one of two training release locations. When they reached criterion for consistent responding, they were given probe trials pseudorandomly interspersed with the training trials in which they were released from one of the three other locations. The 12 test sessions were divided into three phases consisting of four sessions each. A 3 (age groups) x 3 (probe sites) x 3 (phases) mixed design ANOVA with repeated measures on the second and third factors revealed only a significant effect for probe site (F(1,33) = 14.55, p < .01) sing the Geisser-Greenhouse correction for heterogeneity of variance. The pattern of responding most clearly resembled route and was stable over testing. Age was not significant although there was a trend toward random behavior in young and more route-like behavior in older animals. Intrinsic maze cues effects on responding were examined. These data were analyzed using a 3 (age groups) x 2 (training groups) x 3 (probe sites) mixed design ANOVA with repeated measures on the last factor, and again revealed only a significant probe site effect (F(1,33) = 14.55, p < .01). Thus cues intrinsic to the maze did not affect response pattern. Only 13 subjects clearly used one of the three spatial strategies: 6 route, 3 direction, and 4 place. Of the remaining 23 animals 11 were young, 5 were adult and 7 were mature. Two used a variation of place, three used a combination of strategies, four were idiosyncratic, 10 used proto-route (route-like, but not systematic enough to be route) and three were random. The use of place strategy by animals as young as 4 and as old as approximately 17 implicates hippocampal changes occurring outside this age range.