While many researchers have largely focused on principles of systematic desensitization and habituation in explaining fear extinction, these processes have mixed evidence at best. In particular, these models do not account for spontaneous recovery or reinstatement of fear, nor do they explain the context dependency of extinction or rapid reacquisition. This may in part account for the significant number of patients who fail to respond to our available treatments which rely on these principles in designing exposure sessions. However, recent research is converging to suggest that an inhibitory model of fear reduction, in which the original feared association (CS-US) remains but is inhibited by a newly formed association (CS-noUS) representing safety, holds promise in explaining the long-term attenuation of fear and anxiety. This paper reviews research in a number of areas, including neuroimaging, psychophysiology, and psychopharmacology that all provide support for the inhibition model of anxiety. Limitations to this body of research are discussed, along with recommendations for future research and suggestions for improving exposure therapy for fear and anxiety disorders. Clinical implications discussed in this paper include incorporating random and variable practice in exposure sessions, multiple contexts, and pharmacological aides, among others.

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Short-chain fatty acids (SCFAs) are products of microbial fermentation of dietary fiber in the colon and may mediate microbiotagut-brain communication. However, their role in modulating psychobiological processes that underlie the development of stressand anxiety-related disorders is not mechanistically studied in humans. In this triple-blind, randomized, placebo-controlled intervention trial, we examine in a parallel group design the effects of 1-week colonic SCFA-mixture delivery in doses equivalent to fermentation of 10 g or 20 g of arabinoxylan oligosaccharides on responses to psychosocial stress and fear tasks in 66 healthy men. We demonstrate that low and high doses of SCFAs significantly attenuate the cortisol response to psychosocial stress compared to placebo. Both doses of SCFAs increase serum SCFA levels and this increase in circulating SCFAs co-varies significantly with the attenuation of the cortisol response to psychosocial stress. Colonic SCFA delivery does not modulate fecal SCFA concentrations, serum brain-derived neurotrophic factor, cortisol awakening response, fear learning and extinction, or subjective mood ratings. These results demonstrate that colon-delivered SCFAs modulate hypothalamic-pituitary-adrenal axis reactivity to psychosocial stress, thereby supporting their hypothesized role in microbiota-gut-brain communication.

Using a conditioned suppression preparation, the authors investigated sequential (X --> A+/A-) versus simultaneous (XA+/A-) feature positive (FP) discrimination learning in humans. The sequential discrimination was expected to be resolved by means of a Feature X Modulated Target A-US association and the simultaneous discrimination by a feature X-US association. After sequential FP training, extinction of Feature X did not affect discriminative X --> A/A responding (Experiment 1), and X transferred its modulatory ability only to new targets, B, that had also been modulated (Experiment 2). This suggests that the sequential FP discrimination indeed resulted in occasion setting. Unlike expected, Feature X Extinction did not affect discriminative XA/A responding after simultaneous FP training (Experiment 3), while at the same time Feature X did show the predicted nonselective transfer to new targets, B (Experiment 4). J. M. Pearce's (1987) configural learning theory can account for most but not all findings of Experiments 3 and 4.

The current chapter reviews the findings of an ongoing research program suggesting that changes in attitudes can be limited to the context in which counterattitudinal information was learned. The reviewed findings indicate that, although counterattitudinal information may effectively influence evaluations in the context in which this information was learned, previously formed attitudes may continue to influence evaluations in any other context. According to the representational theory of contextualized attitude change, such patterns of contextual renewal occur because exposure to expectancy-violating information enhances attention to context, which leads to an integration of the context into the representation of expectancy-violating counterattitudinal information. The chapter reviews research that (a) tested novel predictions derived from the representational theory of contextualized attitude change, (b) explored the nature of contextualized representations, and (c) investigated the boundary conditions of contextualized attitude change. Theoretical challenges, future directions, and implications for basic and applied research are discussed.