Source Paper
The Role of Ventromedial Prefrontal Cortex in the Recovery of Extinguished Fear
Gregory J. Quirk, Gregory K. Russo, Jill L. Barron, Kelimer Lebron
Journal of Neuroscience • 2000
Fear Conditioning and Extinction
Objective: To examine the role of ventromedial prefrontal cortex (vmPFC) in the acquisition, extinction, and recovery of conditioned fear responses to a tone paired with footshock over a 2-day experiment
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Protocol Steps
Surgical lesion creation
Electrolytic vmPFC lesions were made before training in experimental group. Sham lesions were performed on control group.
Note: Lesions were made prior to any behavioral training. Some lesions spared the caudal infralimbic (IL) nucleus to test regional specificity.
View evidence from paper
“We have reexamined the effects of electrolytic vmPFC lesions made before training on the acquisition, extinction, and recovery of conditioned fear responses”
Day 1 - Acquisition phase
Rats were trained with tone-shock pairings. Conditioned freezing and suppression of bar pressing were measured as indicators of fear acquisition.
Note: vmPFC lesions had no effect on acquisition in this phase
View evidence from paper
“On Day 1 vmPFC lesions had no effect on acquisition or extinction of conditioned freezing and suppression of bar pressing”
Day 1 - Extinction phase
Tone was presented repeatedly in the absence of shock to allow extinction learning. Freezing and bar pressing suppression were measured.
Note: Extinction is thought to involve new learning accompanied by inhibition of conditioned responding rather than erasure of the tone-shock association
View evidence from paper
“Conditioned fear responses to a tone paired with footshock extinguish when the tone is presented repeatedly in the absence of shock”
Day 2 - Recovery/retention test
Rats were re-exposed to the tone to measure recovery of conditioned fear responses after a long delay following extinction training
Note: Sham rats recovered only 27% of acquired freezing, while vmPFC-lesioned rats recovered 86%, indistinguishable from control group that never received extinction
View evidence from paper
“On Day 2 sham rats recovered only 27% of their acquired freezing, whereas vmPFC-lesioned rats recovered 86%, which was indistinguishable from a control group that never received extinction”