A comparative analysis of spatial memory processes

This paper reviews spatial memory processes in three highly evolved taxa: hymenoptera, birds and mammals. In these three taxa, the goal location can be memorized egocentrically as a vector specifying the head-referred direction and the distance to the goal, and/or exocentrically as a view specifying the spatial layout of the surrounding landmarks perceived by the animal when standing at the goal. The egocentric coding process requires a path-integration mechanism to update the memorized goal location as a function of the animal's current position. Changes of direction are estimated allothetically (by reference to an external compass) in hymenoptera, idiothetically (on the basis of internal movement-related information) in mammals, and probably in both ways in birds. Computer simulations have shown that path-integration is very sensitive to random errors occurring in idiothetic but not in allothetic estimations. When using the exocentric coding process, hymenoptera store the bearings and angular sizes of landmarks in a compass-oriented colour snapshot taken at the goal. They ay then return to the goal by moving so as to reduce the discrepancy between the current view of landmarks and the memorized snapshot. In mammals, this process can be accounted for by a neurobiologically plausible model which highlights the fundamental role of exploration of the environment. The way this process is implemented in birds is less clear.