An evaluation of spatial information processing in aged rats.

The spatial learning abilities of young, middle-age, and senescent rats were investigated in two experiments using several versions of the Morns water maze task In Experiment 1, Long-Evans hooded rats were trained to find a submerged escape platform hidden within the water maze During this phase of testing, aged rats exhibited acquisition deficits compared with either young or middle-age subjects With continued training, however, all age groups eventually achieved comparable asymptotic levels of performance Subsequent testing in Experiment 1 revealed that following original training, aged rats were not impaired in learning a novel escape location or in their ability to locate a visible, cued escape platform In an attempt to identify the basis of the age-related impairments observed in Expenment I, naive young and aged rats in Experiment 2 were initially tested for their ability to locate a cued escape platform in the water maze During this phase of testing, the escape latencies of both young and aged rats rapidly decreased to equivalent asymptotic levels Subsequent analyses revealed that following cue training, young subjects exhibit a significant spatial bias for the region of the testing apparatus where the platform was positioned during training In contrast, aged rats showed no spatial bias Training was continued in Expenment 2 using a novel submerged platform location for each subject During these place training trials, the escape latencies of senescent rats were longer than those of young subjects These impairments were also accompanied by a lack of spatial bias among aged rats relative to young control subjects In combination, the results of these investigations indicate that age-related impairments in water maze performance reflect a specific deficit in the ability of aged rats to utilize spatial information In recent years the number of investigation s focusing on the identification of age-related changes in learning and memory has risen dramatically. Related to this intensified research effort is an increasing growth in the proportion of aged individuals in the population Because the incidence of various forms of cognitive deterioration is well documented to increase with increasing age (Botwimck, 1978), an important focus of current research is to delineate age-related changes in learning and memory in laboratory animals Such investigations may, therefore, highlight specific cognitive processes that are compromised in senescence, as well as provide insight into possible neural sites and mechanisms of senescent memory decline. In this context, a number of investigations utilizing a wide range of behavioral testing procedures have demonstrated that the performance of aged animals is impaired relative to young subjects (see Kubams & Zometzer, 1981, for a recent review) Perhaps the most consistent finding across investigations using rodents is that aged rats are impaired in tasks that young animals solve using spatial information Specifically, spatial information processing in aged rats has been studied using a number of testing procedures including the Barnes hole-board task (Barnes, 1979, Barnes, Nadel, & Homg, 1980), the 8-arm