Translating findings from basic fear research to clinical psychiatry in Puerto Rico

Gregory Quirk, Karen Martinez, Lelis, L Nazario Rodríguez, Gregory Quirk
2007 unpublished
Recent advances in the neuroscience of classical fear conditioning from both rodent and human studies are beginning to be translated to the psychiatry clinic. In particular, our understanding of fear extinction as a form of "safety learning" holds promise for the treatment of anxiety disorders in which extinction learning is thought to be compromised. The Department of Psychiatry at the UPR, School of Medicine promotes the development of innovative strategies for treating mental health
more » ... tal health problems. Given the burden resulting from anxiety disorders in Puerto Rico, and the lack of evidence-based treatment practices, there is a pressing need for a future center specializing in the treatment of anxiety related disorders. This center would also serve research and training functions, with the ultimate goal of translating extinction research into clinical practice. This review presents the current developments in extinction research and its relationship to anxiety disorders and treatment. We also analyze the available literature on the epidemiology of anxiety disorders and the existing evidence-based treatments for these conditions. Why research in fear learning? W hile some of our fears may be innate (such as fear of heights or loud noises), the majority of our fears are learned through experience. Fear learning is highly conserved evolutionarily, and is thought to help organisms detect and avoid danger (1-4). In fact, the neural mechanisms of fear learning are remarkably similar across vertebrates. Basic fear memories are formed and stored in the amygdala (5). Expression of fear memories is regulated by the hippocampus and other cortical areas based on contextual or other parameters. Deficits in regulation of fear expression are thought to underlie anxiety disorders such as post-traumatic stress (PTSD) and phobias (6). A convenient model for understanding fear learning is classical fear conditioning in which a sensory stimulus such as a tone is paired with an electric shock. Both humans and rodents rapidly learn that the tone predicts the shock and show conditioned fear responses to the tone. In rodents, this takes the form of freezing, whereas in humans, there is a mild sweating response (skin conductance response, SCR). These learned fear responses can then be correlated with neural activity and pharmacological manipulations. Classical fear conditioning models the "automatic" fear learning that occurs when a person undergoes an aversive or life-threatening event. Overcoming fear through extinction learning The main objective of fear research is to reduce pathological forms of fear and anxiety. An important experimental model of fear inhibition is extinction of conditioned fear, in which the conditioned tone is presented repeatedly without the shock. Under these circumstances, the subject learns that the tone no longer predicts the shock, and fear responses diminish. Indeed, following extinction, the subject responds to the tone as if conditioning never took place. However, it has been known since Pavlov's classic studies with dogs that extinction training does not erase the original fear learning, but is a form of learned inhibition (7). Simple behavioral experiments show that extinguished fear responses can return following the passage of time, or change of context. Thus, extinction training generates a new memory of safety that co-exists with fear memory (Figure 1). Healthy emotional regulation depends on which of these opposing memories is selected for expression at any given time. For this reason, there is considerable recent interest in
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