INTERACTIONS BETWEEN LOCATION AND TASK AFFECT THE SPATIAL AND DIRECTIONAL FIRING OF HIPPOCAMPAL-NEURONS

When rats forage for randomly dispersed food in a high walled cylinder the firing of their hippocampal ''place'' cells exhibits little depen dence on the direction faced by the rat, On radial arm mazes and simil ar tasks, place cells are strongly directionally selective within thei r fields, These tasks differ in several respects, including the visual environment, configuration of the traversable space, motor behavior ( e.g., linear and angular velocities), and behavioral context (e.g., pr esence of specific, consistent goal locations within the environment), The contributions of these factors to spatial and directional tuning of hippocampal neurons was systematically examined in rats performing several tasks in either an enriched or a sparse visual environment, an d on different apparati. Place fields were more spatially and directio nally selective on a radial maze than on an open, circular platform, r egardless of the visual environment, On the platform, fields were more directional when the rat searched for food at fixed locations, in a s tereotypic and directed manner, than when the food was scattered rando mly. Thus, it seems that place fields are more directional when the an imal is planning or following a route between points of special signif icance. This might be related to the spatial focus of the rat's attent ion (e.g., a particular reference point). Changing the behavioral task was also accompanied by a change in firing location in about one-thir d of the cells, Thus, hippocampal neuronal activity appears to encode a complex interaction between locations, their significance and the be haviors the rat is called upon to execute.