Anxiety disorders depend, in part, on alterations in the mechanisms by which fear is learned, stored and expressed in the brain. Much has been learned about the neural basis of fear through studies of Pavlovian fear conditioning, a procedure in which an emotionally neutral conditioned stimulus (CS), such as a tone, is paired with an aversive unconditioned stimulus (US), typically electric shock. Following pairing, the CS acquires the capacity to elicit conditioned responses (CRs), such as freezing behavior and changes in autonomic and endocrine activity, that are part of the organism's defensive repertoire. The neural pathways involved include transmission of CS information from the auditory system to the lateral amygdala (LA), where the CS-US association is formed and stored. The LA then communicates with the central amygdala (CE) via intra-amygdala circuits to control the expression of the conditioned fear reactions. In addition to eliciting fear reactions, an aversive CS also alters instrumental behaviors (actions). For example, patients with anxiety disorders often exhibit behaviors that reduce exposure to fear-eliciting stimuli or situations. So-called avoidance responses can be effective coping strategies, but become problematic when they interfere with daily life. Less is known about the neural basis of fear-based instrumental actions than is known about fear reactions like freezing. In this proposal we use tasks that provide means of assessing how a Pavlovian aversive CS contributes to aversive instrumental action. The traditional task used for this is avoidance conditioning. However, because the Pavlovian and instrumental learning components of the task are intermixed in avoidance conditioning, this procedure is not ideal for examining Pavlovian influences on instrumental behavior. We therefore focus on two tasks that isolate the Pavlovian and instrumental learning phases: escape from fear (EFF) and Pavlovian-to-instrumental transfer (PIT). EFF is particularly useful for exploring how a Pavlovian CS contributes to the acquisition of new instrumental responses. In this task, the CS-US association is first conditioned. Then, in a different situation, the animal learns to perform responses that terminate the CS. CS termination is believed to function as a negative conditioned reinforcer, an event whose termination reinforces behavior. PIT, on the other hand, is useful for exploring how a Pavlovian CS alters the motivation to perform a previously acquired instrumental response. In this task, the CS-US association is also conditioned first and then used to alter the vigor with which the subject performs a previously trained instrumental response. We will use the same CS and US (a tone paired with shock) that we and others have used to identify the brain mechanisms of Pavlovian conditioning. A combination of lesion and inactivation techniques and measurement of physiological activity will be used to examine the contribution of distinct amygdala nuclei and extra-amygdala targets to these tasks. Given existing findings with these and related tasks, we hypothesize distinct roles of three amygdala regions: LA, CE and the basal nucleus (B). In the previous submission, we hypothesized that LA and B would be required in both the EFF and PIT tasks: LA because it stores critical aspects of the CS-US association used in the acquisition of new instrumental responses, and B because it allows the CS to function as a negative conditioned reinforcer in the learning of the instrumental response, and also allows the CS to function as a conditioned incentive in the motivation of performance. Although we proposed that B would be involved in both negative conditioned reinforcement and conditioned motivation, we also proposed that different cells in B would contribute to these processes. New preliminary findings lead to a revised hypothesis. We now propose two different forms of aversive conditioned motivation involving two different amygdala circuits-connections between LA and B are involved in one form and connections from LA to CE in the other. Building on similar (though not identical) findings in appetitive conditioning, we suggest that the LA-B connection is important for using specific information about the CS-US association to motivate behavior, while the LA-CE connection is more important for using the emotional arousal triggered by the CS to motivate behavior. The involvement of B and CE in these forms of motivation is consistent with appetitive findings, but the idea that B and CE contribute to conditioned motivation as distinct outputs of LA diverges with appetitive findings. In addition, we will pursue the output connections of the amygdala in these tasks. We hypothesize that the nucleus accumbens is a potential site where conditioned reinforcement and the two forms of conditioned motivation, processed by distinct outputs from the amygdala, are integrated in the acquisition and performance of aversive instrumental behavior. The studies proposed will provide new information about a how a fear-arousing CS influences instrumental actions by contributing to aversive negative conditioned reinforcement and conditioned motivation. Given that anxiety disorders involve both pathological reactions and actions, the results of this work should greatly extend our understanding of brain circuits relevant to this common class of psychiatric disorders. Better appreciation of aversive instrumental behavior may also provide insight into the relationship between aversive and appetitive processes, and thus may also be relevant to understanding how fear and anxiety contribute to addiction and other disorders that ar traditionally viewed as primarily involving appetitive motivation.
Anxiety disorders involve alterations in threat processing, mediated in part by changes in amygdala structure and function, and are characterized by pathological instrumental actions as well as fear reactions. Much has been learned about the neural basis of Pavlovian fear reactions. In this proposal we hope to elucidate the circuits underlying fear-based instrumental actions. Such studies of Pavlovian-instrumental interactions will help elucidate anxiety disorders and hopefully lead to improved treatments of these debilitating conditions.
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