Different mechanisms of fear extinction dependent on length of time since fear acquisition.

  title={Different mechanisms of fear extinction dependent on length of time since fear acquisition.},
  author={Karyn M. Myers and Kerry James Ressler and Michael Davis},
  journal={Learning \& memory},
  volume={13 2},
Fear extinction is defined as a decline in conditioned fear responses (CRs) following nonreinforced exposure to a feared conditioned stimulus (CS). Behavioral evidence indicates that extinction is a form of inhibitory learning: Extinguished fear responses reappear with the passage of time (spontaneous recovery), a shift of context (renewal), and unsignaled presentations of the unconditioned stimulus (reinstatement). However, there also is evidence to suggest that extinction is an "unlearning… 

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Timing of extinction relative to acquisition: a parametric analysis of fear extinction in humans.

The results remain inconclusive regarding spontaneous recovery and the timing of extinction and are discussed in terms of performing translational studies of fear in humans.

Immediate extinction promotes the return of fear

Evidence for recovery of fear following immediate extinction in rats and humans.

Evidence is found for spontaneous recovery and reinstatement in both rats and humans even when extinction was conducted immediately after fear learning, which does not support the hypothesis that immediate extinction erases the original memory trace and suggests that a close temporal proximity of therapeutic intervention to the traumatic event might be advantageous.

Early extinction after fear conditioning yields a context-independent and short-term suppression of conditional freezing in rats.

The results suggest that fear suppression under immediate extinction may be due to a short-term, context-independent habituation process, rather than extinction per se.

Evidence for the persistence of contextual fear memories following immediate extinction

Overall, the results provide little evidence that extinction conducted immediately after conditioning destroys or erases the original memory trace.

Exposure to a fearful context during periods of memory plasticity impairs extinction via hyperactivation of frontal-amygdalar circuits.

The results show that long-term extinction is impaired when it occurs during time periods during which the memory should be most vulnerable to disruption (soon after conditioning or retrieval), and behavioral effects are correlated with hyperactivation of medial prefrontal cortex and amygdala subregions associated with fear expression rather than fear extinction.

Delayed extinction attenuates conditioned fear renewal and spontaneous recovery in humans.

The authors conclude that the passage of time allows for memory consolidation processes to promote the formation of distinct yet flexible emotional memory traces that confer an ability to recall extinction, even in an alternate context, and minimize the return of fear.

Long-Term Neural Correlates of Reversible Fear Learning in the Lateral Amygdala

It is shown that the ensemble activity of all recorded LA neurons correlates tightly with conditioned fear responses of rats in a conditioning/extinction/reconditioning paradigm spanning 3 d, and the existence of distinct populations encoding various facets of fear memory is suggested.

Expression of renewal is dependent on the extinction-test interval rather than the acquisition-extinction interval.

The failure to see renewal 10 min after extinction suggests that there is a separate context memory that undergoes a different consolidation function than the CS-no US memory formed during extinction, and the expression of extinction appears to be GABA dependent regardless of the extinction-test interval or the test context.



Memory for extinction of conditioned fear is long-lasting and persists following spontaneous recovery.

  • G. Quirk
  • Psychology, Biology
    Learning & memory
  • 2002
Complete spontaneous recovery indicates that extinction training given 1 h after conditioning does not interfere with the consolidation of conditioning memory, and supports the idea that conditioning and extinction of fear are learned by independent systems, each able to retain a long-term memory.

The Role of Ventromedial Prefrontal Cortex in the Recovery of Extinguished Fear

The effects of electrolytic vmPFC lesions made before training on the acquisition, extinction, and recovery of conditioned fear responses in a 2 d experiment suggest a role of thevmPFC in consolidation of extinction learning or the recall of contexts in which extinction took place.

Evidence that GABA transmission mediates context-specific extinction of learned fear

The present findings indicate that GABA transmission at GABAA receptors is involved in the inhibition of extinguished fear, and that this effect of GABA is regulated by those cues that constitute the extinction context.

Context-Dependent Neuronal Activity in the Lateral Amygdala Represents Fear Memories after Extinction

Context-dependent neuronal activity in the lateral nucleus of the amygdala may be an important mechanism for disambiguating the meaning of fear signals, thereby enabling appropriate behavioral responses to such stimuli.

Reinstatement of fear to an extinguished conditioned stimulus.

  • R. RescorlaC. Heth
  • Psychology, Biology
    Journal of experimental psychology. Animal behavior processes
  • 1975
Four experiments are reported which demonstrate the ability of an unconditioned stimulus (UCS) presentation following extinction to partially reinstate the conditioned response. These experiments are

Neurons in medial prefrontal cortex signal memory for fear extinction

It is suggested that consolidation of extinction learning potentiates infralimbic activity, which inhibits fear during subsequent encounters with fear stimuli, indicating that medial prefrontal cortex might store long-term extinction memory.

Contextual control of the extinction of conditioned fear: tests for the associative value of the context.

  • M. BoutonD. A. King
  • Psychology, Biology
    Journal of experimental psychology. Animal behavior processes
  • 1983
The results suggest that fear of an extinguished CS can be affected by the excitatory strength of the context but that independently demonstrable contextual excitation or inhibition is not necessary for contexts to control that fear.

Treatments that weaken Pavlovian conditioned fear and thwart its renewal in rats: implications for treating human phobias.

Evidence suggested that the ability of fear-weakening treatments to prevent fear renewal reflected the combined effects of transfer of extinction across treatment and test contexts and habituation to the unconditioned stimulus.