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Molecular Psychiatry (2007) 12, 120150 & 2007 Nature Publishing Group All rights reserved 1359-4184/07 $30.00 www.nature.com/mp
FEATURE REVIEW
Mechanisms of fear extinction
KM Myers1,2 and M Davis1,2,3
1Center for Behavioral Neuroscience, Emory University, Atlanta, GA, USA; 2Yerkes National Primate Research Center, Emory University, Atlanta, GA, USA and 3Departments of Psychiatry, Behavioral Sciences, and Psychology, Emory University, Atlanta, GA, USA
Excessive fear and anxiety are hallmarks of a variety of disabling anxiety disorders that affect millions of people throughout the world. Hence, a greater understanding of the brain mechanisms involved in the inhibition of fear and anxiety is attracting increasing interest in the research community. In the laboratory, fear inhibition most often is studied through a procedure in which a previously fear conditioned organism is exposed to a fear-eliciting cue in the absence of any aversive event. This procedure results in a decline in conditioned fear responses that is attributed to a process called fear extinction. Extensive empirical work by behavioral psychologists has revealed basic behavioral characteristics of extinction, and theoretical accounts have emphasized extinction as a form of inhibitory learning as opposed to an erasure of acquired fear. Guided by this work, neuroscientists have begun to dissect the neural mechanisms involved, including the regions in which extinction-related plasticity occurs and the cellular and molecular processes that are engaged. The present paper will cover behavioral, theoretical and neurobiological work, and will conclude with a discussion of clinical implications.
Molecular Psychiatry (2007) 12, 120150. doi:10.1038/sj.mp.4001939; published online 12 December 2006
Keywords: learning; memory; pavlovian conditioning; exposure therapy
Introduction In recent years a great deal has been learned about the behavioral characteristics and neural mechanisms of fear acquisition (for reviews see Davis,1 Rodrigues et al.2). Much of this progress may be attributed to the use of Pavlovian fear conditioning as a model system.In this paradigm, an initially innocuous stimulus (the to-be conditioned stimulus CS; for example, a light, tone, or distinctive place) is paired with an innately aversive unconditioned stimulus (US; e.g., a footshock) and the subject (typically a rat or mouse) comes to exhibit a conditioned fear response (CR) to the CS. In rodents, fear is defined operationally as a cessation of all bodily movements except those required for respiration (freezing), an increase in the amplitude of...