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Impaired Extinction: my reading

Each paper in the “My Reading” series is an interpretation of a scientific paper on a topic of interest to animal trainers. This paper is presented to look for parameters offering potential for fear reduction .

Rodent models of impaired fear extinction.

READ — Date: 13 March 2020 Reason: exposure therapy project

CITATION: Singewald, N., & Holmes, A. (2019). Rodent models of impaired fear extinction. Psychopharmacology236(1), 21-32.

KEYWORDS: fear network, inhibition network__

QUESTIONS ASKED: What are the current models for the impairment of extinction and what are the general approaches to support extinction learning and retention? How can animal models be used in this research?

METHOD/APPROACH: A review article.

SIGNIFICANCE: An animal (rat) centric review and list of studies give a glimpse into practices that do not rely on human cognition.

KEY CONCEPTS: Failure to build and maintain strong fear inhibitory associations may explain many of the failures seen in exposure therapy.

The CS comes to elicit some form of fear/anxiety/defensive CR. If the CR can be measured, it can be used to measure fear.

Singewald et al, 2019. Rodent Models of Impaired Extinction
Singewald et al, 2019. Typical Causes of Impairment

Drugs, diet, and stress can impair extinction. Stress is also partially determined by the genetics and history of the individual. Although the model treats things as separate (see Fig 3), they are very interconnected. Drugs can impair acquisition or retention of extinction, but other substances can be used to enhance the same processes. Generalization regarding these factors is difficult.

Genetic variation can act at any level (any type of subdivision of population). There are individual differences and group differences. Studies of extinction impaired strains of mice showed that acquisition and retention of extinction are very different processes. In humans, several specific alleles have been seen to be predictive of PTSD, showing a variety of mutations can lead to the problem.

The principle elements of the network involved in fear extinction are the PFC, the HPC, and the AMY. The supporting structures include the PAG, the BNST, the VTA, and the Striatum. (see Quirk and Mueller, 2009 for review)

Learning and memory for extinction is distributed in a network fashion across these parts of the brain. There are many nodes in these systems. Researchers note excess or deficits in their activity can result in problems in the acquisition or retention of extinction. The activity can be studied in vivo by looking at the resting metabolic activity of the brain. Mapping these networks is a current trend in PTSD research.


  • Extinction: reduction of conditioned responses, in this article reduction of conditioned fear.
  •  Acquisition of extinction: initial learning where fear is declining within an extinction training session.
  • Consolidation of extinction: a period in which the brain physically changes its structure in response to extinction.
  • Retrieval of extinction: the subsequent response to the fear stimulus as moderated by the extinction learning. Poor retrieval results in more fear. Causes of poor retrieval can include spontaneous recovery, renewal, and reinstatement.


  • Can diet be a factor in equine fear?
  •  How do the medications we give equines influence fear levels?
  • Is there a way to compare breeds or even herds for genetic fear?
  • Are animals that are socially awkward in the herd (few friends) more fearful outside of the herd?
  • Does the CR have to be specific to the CS or would a generalized CR (ie. snorting at novel objects) cloud our ability to measure fear?
  • Is there a way to screen for the ability to build strong fear inhibitory systems?
  • If we have a fearful equine, is there a way to test for inhibition of extinction?
  • What drugs might accelerate the acquisition of extinction in the equine?
  • What drugs might enhance the retrieval of extinction?

Extra: Good video on the complexity of the brain.

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