On the role of the hippocampus in memory: information processing versus memory system

Quinolinic acid lesion of the rat entorhinal cortex pars medialis produces selective amnesia in allocentric working memory (WM), but not in egocentric WM

The functional role of the entorhinal cortex pars medialis in memory formation was investigated by lesioning this area with quinolinic acid, a selective agonist of the NMDA-subtype of glutamate receptors which has neurotoxic properties. With this technique "en passant" axons are spared and only neurons of the target area are destroyed. The effects of this lesion on learning abilities in the 8-arm maze were tested. Rats in the lesion group showed different exploring behavior: animals did not visit all arms, and previously visited arms were reentered. When orienting themselves on distal cues (allocentric tests) the animals showed working memory (WM) deficits and reduced speed of acquisition of reference memory (RM). When changing arms that were baited, the test group had difficulties learning the new task. Performance decreased after introduction of a delay. However, when orienting themselves on proprioceptive cues (egocentric tests), no deficits in memory formation were detectable. Animals appeared hypomotoric in all tests.

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.