A rifle shot registers around 120 to 155 decibels. As soon as Asencio’s ears detected the booming gunshots, before he even realized what they were or that he was afraid, a signal traveled to his brain by way of the auditory nerve. When the signal reached his brainstem, neurons passed along the information to his amygdala, an ancient, almond-shaped mass of nuclei located deep within his brain’s temporal lobes that is central to the human fear circuit. In response, the amygdala set off a cascading series of changes throughout his body. In a flash, Asencio transformed into survival mode—without
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