Retrograde and anterograde memory following selective damage to the dorsolateral entorhinal cortex

Abstract

Anatomical and electrophysiological evidence suggest the dorsolateral entorhinal cortex (DLEC) is involved in processing spatial information, but there is currently no consensus on whether its functions are necessary for normal spatial learning and memory. The present study examined the effects of excitotoxic lesions of the DLEC on retrograde and anterograde memory on two tests of allocentric spatial learning: a hidden fixed-platform watermaze task, and a novelty-preference-based dry-maze test. Deficits were observed on both tests when training occurred prior to but not following n-methyl d-aspartate (NMDA) lesions of DLEC, suggesting retrograde memory impairment in the absence of anterograde impairments for the same information. The retrograde memory impairments were temporally-graded; rats that received DLEC lesions 1-3 days following training displayed deficits, while those that received lesions 7-10 days following training performed like a control group that received sham surgery. The deficits were not attenuated by co-infusion of tetrodotoxin, suggesting they are not due to disruption of neural processing in structures efferent to the DLEC, such as the hippocampus. The present findings provide evidence that the DLEC is involved in the consolidation of allocentric spatial information.

Keywords: Allocentric spatial memory; Anterograde memory; Entorhinal cortex; Lesion; Rat; Retrograde amnesia.