BRAIN AGING - IMPAIRED CODING OF NOVEL ENVIRONMENTAL CUES

Studies of the spatial memory capacities of aged animals usually focus on performance during the learning of new environments. By contrast, efforts to characterize age-related alterations in spatial firing info rmation processing by hippocampal neurons typically use an environment that is highly familiar to the animals. In the present study we compa red the firing prop erties of hippocampal neurons in young adult and a ged rats as they acquired spatial information about new environmental cues. Hippocampal complex spike cells were recorded while rats perform ed a radial arm maze task in a familiar environment and then recorded again after many of the spatial cues were changed. After the change in the environment, in aged rats 35-42% of place fields retained their o riginal shape and location with respect to the maze center, although t hey usually rotated to another arm. By contrast, all place fields in y oung animals either disappeared or appeared in a new location. Some of the new place fields appeared in the new environment during the first 5 min of exploration, whereas others needed more than 30 min to devel op fully. In the familiar environment spatial selectivity of place cel ls was similar in young and aged rats. By contrast, when rats were pla ced into a new environment, spatial selectivity decreased considerably in aged memory-impaired rats compared with that of young rats and age d rats with intact memory performance.