Delayed Recall of Fear Extinction in Rats with Lesions of Ventral Medial Prefrontal Cortex

Extinction of auditory fear conditioning is thought to form a new memory. We previously found that rats with vmPFC lesions could extinguish fear to the tone within a session, but showed no recall of extinction 24 h later. One interpretation is that the vmPFC is the sole storage site of extinction me...

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Bibliographic Details
Published in:Learning & memory (Cold Spring Harbor, N.Y.) N.Y.), 2004-09, Vol.11 (5), p.544-548
Main Authors: Lebron, Kelimer, Milad, Mohammed R, Quirk, Gregory J
Format: Article
Language:English
Subjects:
Acoustic Stimulation
Animals
Association Learning - physiology
Auditory Stimuli
Brain
Conditioning
Conditioning, Classical - physiology
Conditioning, Operant - physiology
Extinction, Psychological - physiology
Fear
Fear - physiology
Male
Memory
Mental Recall - physiology
Prefrontal Cortex - physiology
Rats
Rats, Sprague-Dawley
Recall (Psychology)
Reinforcement Schedule
Time Factors
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Summary:Extinction of auditory fear conditioning is thought to form a new memory. We previously found that rats with vmPFC lesions could extinguish fear to the tone within a session, but showed no recall of extinction 24 h later. One interpretation is that the vmPFC is the sole storage site of extinction memory. However, it is also possible that lesioned rats were unable to retrieve extinction memory stored in other structures. To determine if a latent extinction memory could be retrieved with additional training, we repeated the experiment but added an additional 5 d of extinction reminder trials. Replicating our previous findings, vmPFC-lesioned rats extinguished normally on day 1, but showed no recall of extinction on day 2. Over the next 5 d, however, lesioned rats showed significant savings in their rate of re-extinction. Thus, the vmPFC is not the only site where extinction memory is stored. Nevertheless, lesioned rats receiving only two extinction trials per day required twice as many days to initiate extinction as controls. Although recall of extinction is possible without the vmPFC, it is significantly delayed. We suggest that the vmPFC accelerates extinction by permitting access to recently learned extinction trials, thereby maximizing behavioral flexibility. (Contains 3 figures.)
ISSN:1072-0502
1549-5485
DOI:10.1101/lm.78604