Explicit and ambiguous threat processing: Functionally dissociable roles of the amygdala and bed nucleus of the stria terminalis

Highly influential models have proposed that responses to different types of threat are mediated by partially segregated neural systems, with the amygdala underlying phasic responses to explicit threat (fear) and the bed nucleus of the stria terminalis (BNST) mediating sustained responses to ambiguous threat (anxiety). However, newer models have suggested similar recruitment of both regions across a wide spectrum of threat. Therefore, to empirically test these models and further elucidate the activation profiles and connectivity patterns of the amygdala and the BNST during threat processing, 20 participants were scanned using high-resolution fMRI (1.5 mm³). Using fearful faces and human screams as aversive stimuli, two threat conditions were created: Explicit Threat in which threats were certain and predictable (fear) and Ambiguous Threat in which threats were uncertain and unpredictable (anxiety). Results indicated that, although the amygdala and the BNST both showed heightened engagement across both threat conditions, the amygdala showed preferential engagement during Explicit Threat and displayed functional connectivity with regions involved in stimulus processing and motor response. By contrast, the BNST preferentially responded during Ambiguous Threat and exhibited functional connectivity with prefrontal regions underlying interoception and rumination. Furthermore, correlations with questionnaires measuring trait anxiety, worry, and rumination suggested that individual differences in affective style play a modulatory role in regional recruitment and network connectivity during threat processing.