A 2005 poll of U.S. teenagers revealed the power that emotion can have in searing fear-filled memories deeply; despite the teens' limited direct experience, terrorist attacks, war, and nuclear war held top-ten berths in a list of fears. This finding hints at a phenomenon that Hadjikhani and her colleagues study: the contagion of fear. In her research, Hadjikhani has found that humans, like other animals, can experience fear indirectly, the result of another's glance or muscle tensing, or, on a larger scale, that electric connection that turns a milling crowd into a stampeding throng.
We're born into this world with a system to read other people's expressions, says Hadjikhani. Ten minutes after we're born, we're already oriented more to faces than to objects. In 2009, Hadjikhani and colleagues reported on their investigation of one aspect of facial expression-the gaze-and its role in communicating danger. They found that while a direct gaze from a fear-filled face triggers activity in fear-response regions of the brain, the response is not as complex as that elicited by a fear-filled face in which the eyes are averted. A direct gaze signals an interaction between participants who know themselves to be non-threatening. But an averted gaze, pointing with the eyes, as the researchers call it, flags a possible environmental danger and sparks activity in brain regions skilled at reading faces, interpreting gazes, processing fear, and detecting motion.
In other research, Hadjikhani found that the brain can recognize happy and fearful expressions in body movements. A fearful posture-hands held open and in front of the body like shields, for example-activates brain regions that oversee emotion, vision, and action, while postures of happiness-arms loosely held from the body as if opened to embrace-spur activity only in vision-processing regions.
These physical communications of actual or perceived danger offer one avenue to developing a conditioned fear, a learned response founded upon emotion and impressed so firmly within memory that it remains active for a lifetime.
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