Hippocampus, maps, and memory: toward a rapprochement

Psychobiological evidence for the distinction between episodic and semantic memory

The evidence for discrete neurobiological mechanisms that underlie episodic and semantic memory is reviewed. Published data from three separate lines of research are considered: studies of human amnesic patients, psychopharmacological studies of normal human subjects, and studies of working and reference memory in rodents, a distinction that is arguably analogous to the episodic/semantic dichotomy. It is concluded that the available evidence does not indicate that episodic and semantic memory are mediated by discrete neural subsystems. An alternative model of human memory is discussed, based on the concept of parallel distributed processing.

The radial maze performance of mice: assessing the dimensional requirements for serial order memory in animals

Two versions of the eight-arm radial maze were used to test the working memory abilities of CD-1 mice. In an elevated open-arm radial maze, mice quickly and successfully learned the multiple-choice procedure. However, mice trained in an enclosed-arm radial maze mastered the task only by developing a kinesthetic strategy of response. When a delay was imposed between choices 4 and 5, mice in the open-arm radial maze retained high performance levels. Choice accuracy declined markedly for mice in the enclosed-arm radial maze under delay conditions. Transference of the two groups of mice between the two mazes resulted in a complete reversal of sampling strategies. Minor changes to the enclosed-arm maze and room illumination permitted mice to successfully perform in the non-egocentric manner which they exclusively employed in the open-arm maze. The results show that mice can demonstrate a working memory capacity when in an environmentally adequate radial maze, and provide evidence against the existence of nonspatial working memory ability. The discussion examines the procedural and environmental requirements for displays of working memory, and a set of hypotheses is presented which serve to integrate the working memory and cognitive mapping theories.