DavisM1992a - Annual Reviews www.annualreviews.org/aronline...

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Annu. Reo. NeuroscL 1992. 15:353-75 Copyright © 1992 by Annual Reviews Inc. All rights reserved THE ROLE OF THE AMYGDALA IN FEAR AND ANXIETY Michael Davis Ribicoff Research Facilities of the Connecticut Mental Health Center, Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut 06508 KEY WORDS: learning, memory, conditioning INTRODUCTION Converging evidence now indicates that the amygdala plays a crucial role in the development and expression of conditioned fear. Conditioned fear is a hypothetical construct used to explain the cluster of behavioral effects produced when an initially neutral stimulus is consistently paired with an aversive stimulus. For example, when a light, which initially has no behavioral effect, is paired with an aversive stimulus such as a footshock, the light alone can elicit a constellation of behaviors that are typically used to define a state of fear in animals. To explain these findings, it is generally assumed (cf. McAllister & McAllister 1971) that during light-shock pair- ings (training session), the shock elicits a variety of behaviors that can used to infer a central state of fear (unconditioned responses--Figure 1). After pairing, the light can produce the same central fear state and thus the same set of behaviors formerly produced by the shock. Moreover, the behavioral effects that are produced in animals by this formerly neutral stimulus (now called a conditioned stimulus--CS) are similar in many respects to the constellation of behaviors that are used to diagnose gener- alized anxiety in humans (Table 1). This chapter summarizes data sup- porting the idea that the amygdala, and its many efferent projections, may represent a central fear system involved in both the expression and acquisition of conditioned fear. 353 0147~306X/92/0301~)353502.00 www.annualreviews.org/aronline Annual Reviews Annu. Rev. Neurosci. 1992.15:353-375. Downloaded from arjournals.annualreviews.org by University of Wisconsin - Madison on 10/23/07. For personal use only.
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354. DAVIS Light --- Tone --- Shock Puff --- Increased heart rate ~ Decreased salivation Stomach u~cers Respiration change Scanning and vigilance Urination, Defecation Increased Startle Grooming Freezing Increased heart rate .rii!!t~ Decreased salivation Stomach ulcers Respiration change Scanning and vigilance Urination, Defecation Increased Startle Grooming Freezing Fioure 1 General scheme believed to occur during classical conditioning with an aversive conditioned stimulus. During training, the aversive stimulus (e.g. shock) activates a central fear system that produces a constellation of behaviors generally associated with aversive stimuli (unconditioned responses). After consistent pairings of some neutral stimulus such as a light or tone or puff of air with shock during the training phase, the neutral stimulus is capable of producing a similar fear state and hence the same set of behaviors (conditioned responses), for~nerly only produced by the shock. Tabl[e 1 Comparison of measures in animals typically used to index fear and those in the
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DavisM1992a - Annual Reviews www.annualreviews.org/aronline...

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