Leaving a toxic relationship is supposed to feel like freedom. And in many ways it does, but for a significant number of survivors, freedom arrives accompanied by an unwanted passenger: a nervous system that cannot stop scanning for danger. Doors that open too fast, a raised voice in the other room, a partner's unexplained silence, stimuli that would hardly mean anything to an average person but can trigger a chain reaction of anxiety in the mind of someone who has experienced repeated relational abuse. This is hypervigilance, and it does not fade away just because the threat has been eliminated. What the new neuroscience can make evident is that this is not weakness, hypersensitivity, or failure to move on. It is a quantifiable, biological re-shuffling of the brain threat-detection system, one that starts at the amygdala, proceeds through the hypothalamic-pituitary-adrenal (HPA) axis, and reinvents the very patterns in which attention…