Threat, domain-specificity and the human amygdala.

It is well documented that the human amygdala responds strongly to human faces, especially when depicting negative emotions. The extent to which the amygdala also responds to other animate entities - as well as to inanimate objects - and how that response is modulated by the object's perceived affective valence and arousal value remains unclear. To address these issues, subjects performed a repetition detection task to photographs of negative, neutral, and positive faces, animals, and manipulable objects equated for emotional valence and arousal level. Both the left and right amygdala responded more to animate entities than manipulable objects, especially for negative objects (fearful faces, threatening animals, versus weapons) and to neutral stimuli (faces with neutral expressions, neutral animals, versus tools). Thus, in the absence of contextual cues, the human amygdala responds to threat associated with some object categories (animate things) but not others (weapons). Although failing to activate the amygdala, relative to viewing other manipulable objects, viewing weapons did elicit an enhanced response in dorsal stream regions linked to object action. Thus, our findings suggest two circuits underpinning an automatic response to threatening stimuli; an amygdala-based circuit for animate entities, and a cortex-based circuit for responding to manmade, manipulable objects.