1. An almond-shaped neuro structure involved in producing and responding to nonverbal signs of anger, avoidance, defensiveness, and fear.
2. A small mass of gray matter that inspires aversive cues, such as the freeze reaction, sweaty palms, and the tense-mouth display.
3. A primeval arousal center, originating in early fishes, which is central to the expression of negative emotions in man.