Behavioral correlates of denervation and reinnervation of the hippocampal formation of the rat: open field activity and cue utilization following bilateral entorhinal cortex lesions.
Bilateral lesions of the entorhinal cortex (E.C.) of the rat result in persistent deficits in both spontaneous and reinforced alternation. The present study analyzes the nature of this impairment. To determine if changes in exploratory activity accompanied the deficits in alternation, open field activity was measured daily from 2-22 days following bilateral E.C. lesions. Such lesions resulted in a pronounced transient increase in open field activity which peaked between 5 and 7 days postlesion, but subsequently decreased to near preoperative levels at approximately 11 days postlesion. Alternation performance was also analyzed, to determine which cues are utilized to make the alternation, and whether cue utilization is affected by bilateral E.C. lesions. Utilizing a plus (+) maze, animals readily learned to alternate goal arms, but even with extensive training, failed to learn to alternate turns (left and right). However, the ability to identify the two goal arms in a nonalternation situation (which does not require short term recall of the preceding trial) was not permanently impaired by bilateral E.C. lesions. Since bilateral E.C. lesions do not result in persistent deficits in the ability to identify the two goal arms, but do disrupt alternation performance, we hypothesize that the deficit in alternation might reflect an inability to recall which arm was chosen on preceding trials. The implications of these results for an understanding of the behavioral consequences of postlesion reorganization of neuronal circuitry are discussed.
D000818:Animals; D003463:Cues; D003714:Denervation; D006624:Hippocampus / Q000502:physiology*; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009416:Nerve Regeneration; D051381:Rats; D013997:Time Factors