Expose subjects to evidence of someone else in pain. If their heart rate...

Expose subjects to evidence of someone else in pain. If their heart rate increases a lot {a peripheral indicator of anxious, amygdaloid arousal}, they are unlikely to act prosocially in the situation. The prosocial ones are those whose heart rates decrease; they can hear the sound of someone else's need instead of the distressed pounding in their own chests.

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