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Amygdala and hippocampal activity during acquisition and extinction of human fear conditioning. Cogn Affect Behav Neurosci 4:317-325

University of Wisconsin, Milwaukee, Wisconsin 53201, USA.
Cognitive Affective & Behavioral Neuroscience (Impact Factor: 3.21). 10/2004; 4(3):317-25. DOI: 10.3758/CABN.4.3.317
Source: PubMed

ABSTRACT Previous functional magnetic resonance imaging (fMRI) studies have characterized brain systems involved in conditional response acquisition during Pavlovian fear conditioning. However, the functional neuroanatomy underlying the extinction of human conditional fear remains largely undetermined. The present study used fMRI to examine brain activity during acquisition and extinction of fear conditioning. During the acquisition phase, participants were either exposed to light (CS) presentations that signaled a brief electrical stimulation (paired group) or received light presentations that did not serve as a warning signal (control group). During the extinction phase, half of the paired group subjects continued to receive the same treatment, whereas the remainder received light alone. Control subjects also received light alone during the extinction phase. Changes in metabolic activity within the amygdala and hippocampus support the involvement of these regions in each of the procedural phases of fear conditioning. Hippocampal activity developed during acquisition of the fear response. Amygdala activity increased whenever experimental contingencies were altered, suggesting that this region is involved in processing changes in environmental relationships. The present data show learning-related amygdala and hippocampal activity during human Pavlovian fear conditioning and suggest that the amygdala is particularly important for forming new associations as relationships between stimuli change.

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    • "This hypothesis is also supported by findings of rapid amygdala habituation during repeated exposure to generally aversive (Wendt, Weike, Lotze, and Hamm, 2011) or fear-relevant pictures (Wendt, Schmidt, Lotze, and Hamm, 2012). In the current study, however, we could not confirm the hypothesis suggested by Knight et al. (2004) that the amygdala detects changes in CS–UCS associations. Although participants had to learn a new association of the UCS and a novel geometric shape in each run, the initial amygdala differentiation between CS+ and CS− cue onset did not reappear at the first trial block of the second and third run. "
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    • "Selective lesions to the amygdala impair both cued and contextual fear conditioning in animals (LeDoux, 2000). Similarly, amygdala activity increases during the acquisition relative to the extinction phase (Phelps et al., 2001; Knight et al., 2004), and there is a strong correlation between amygdala reactivity and conditioned SCRs during fear acquisition (Cheng et al., 2003; Phelps et al., 2004) in humans. The amygdala is also involved in the fast detection of potentially harming stimuli (LeDoux, 2000; Öhman and Mineka, 2001), which might represent a highly adaptive process. "
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    • "Increased activation of the amygdala can be observed during the beginning of extinction learning. With increasing duration of extinction, activation of the amygdala decreases (Knight, Smith, Cheng, Stein, & Helmstetter, 2004). The recall of extinction memory is associated with the activation of the prefrontal cortex (Milad et al., 2007). "
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