How does trauma affect the nervous system?

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Trauma alters nervous system architecture by conditioning the threat-detection system to treat non-threatening situations as dangerous, dysregulating the stress hormone cascade, fragmenting the brain's capacity to integrate experience, and storing unprocessed events in the body as chronic activation. The amygdala, the brain's threat-detection center, is the first structure to respond to perceived danger. Dr. Joseph LeDoux at New York University demonstrated that the amygdala processes threat information faster than the cortex — creating emotional and physical responses before conscious thought. Trauma sensitizes the amygdala, lowering its activation threshold. During traumatic events, the hippocampus — which contextualizes memory in time — can be temporarily suppressed by cortisol flooding. Dr. Bessel van der Kolk documented that this is why traumatic memories often surface as sensory fragments, body sensations, or images rather than linear narrative: the hippocampus was offline during encoding. Chronic trauma elevates baseline cortisol and dysregulates the HPA (hypothalamic-pituitary-adrenal) axis, the brain's stress hormone control system. This manifests as hypervigilance, difficulty sleeping, digestive issues, immune dysregulation, and chronic pain. Healing requires both bottom-up approaches (somatic, breath, movement — working with the body's stored activation) and top-down approaches (therapy, narrative, understanding — working with the story). Neither alone is sufficient for full resolution.