Why traumatic memories feel different
When someone experiences a traumatic event, the brain’s normal memory consolidation process is disrupted. Under ordinary circumstances, the hippocampus integrates sensory, emotional, and contextual information into a coherent narrative that gets stored in long-term memory. During trauma, however, the intense stress response — driven by cortisol and noradrenaline flooding the brain — impairs hippocampal function. What gets encoded instead is a fragmented collection of sensory traces: images, smells, sounds, bodily sensations, and fragments of language that are never woven together into a coherent story (van der Kolk, 1994; Brewin et al., 2010).This is compounded by dissociation. When an experience is overwhelming, the brain partially disconnects from it as a protective mechanism, which means encoding is incomplete from the start (Lanius et al., 2010). The result is what researchers call dual representation: the trauma exists as a set of sensory-perceptual fragments (sometimes called “situationally accessible memories”) rather than as a verbally integrated, autobiographical memory (Brewin et al., 1996, 2010).
Why the nervous system stays dysregulated
These unconsolidated fragments don’t sit quietly in storage. Because they were never integrated into a past-tense narrative — something that happened — the brain continues to treat them as a present, ongoing threat. Any sensory cue that matches a fragment (a smell, a sound, a posture) can trigger a retrieval response, pulling the person back into the original experience as if it were happening now. This is the neurological basis of flashbacks and intrusive symptoms (Ehlers & Clark, 2000).
This keeps the nervous system in a chronically activated state. The threat-detection circuitry — particularly the amygdala — remains on high alert, perpetually scanning for danger. At the same time, the prefrontal cortex, which would normally regulate this response and help contextualize the memory as in the past, is functionally suppressed by the ongoing stress response (Shin et al., 2006). The brain is caught between two competing impulses: a biological drive to complete consolidation of the memory, and a self-protective drive to avoid the pain of doing so. Both are metabolically costly. This chronic tension — approach and avoidance simultaneously active — is a core reason people with trauma histories often feel depleted, hypervigilant, and unable to fully relax.
What treatment is trying to do
Effective trauma therapies share a common mechanism: they create conditions in which the fragmented memory can surface within a window of tolerance — a state of activation that is sufficient to access the material, but not so overwhelming that it triggers full re-traumatization (Ogden et al., 2006; Siegel, 1999). When the nervous system is within that window, the hippocampus can re-engage, and the brain gets an opportunity to do what it has been trying to do all along: integrate the fragments into a coherent, past-tense narrative and move it into long-term storage, where it is no longer “online” as an active threat.
EMDR is thought to facilitate this through bilateral stimulation — typically eye movements — while the client holds the traumatic material in mind. The leading theoretical account (though still debated) is that the bilateral stimulation taxes working memory just enough to reduce the vividness and emotional charge of the memory while keeping it accessible, and that this state approximates the neurological conditions of REM sleep, during which normal memory consolidation occurs (Shapiro, 2018; Stickgold, 2002). Each session allows more fragments to be integrated, reducing the amount of unprocessed material that the brain must continually manage.
Somatic therapies — including Somatic Experiencing and Sensorimotor Psychotherapy — start from the observation that trauma is held in the body as much as the mind. Levine’s foundational insight was that animals surviving threat instinctively complete the defensive motor responses activated during danger — shaking, trembling, orienting — and that this discharge allows the nervous system to return to baseline (Levine, 1997). In humans, social and cognitive inhibition prevents this completion, leaving the autonomic nervous system stuck in sympathetic hyperarousal or dorsal vagal shutdown, as described by Porges’ Polyvagal Theory (Porges, 2011). Somatic therapies work by tracking bodily states in real time and facilitating the completion of these interrupted responses through small, titrated movements and sensations — allowing the nervous system to discharge accumulated activation and restore regulatory flexibility without requiring the client to revisit the narrative of what happened (Levine, 2010; Ogden et al., 2006).
Internal Family Systems (IFS) understands traumatic material as carried by exiled parts — aspects of the self overwhelmed during the trauma and locked away by protective parts whose job is to keep that pain out of awareness (Schwartz, 1995). The nervous system dysregulation of trauma is, in this view, the metabolic cost of those protectors working constantly to suppress the exile. Treatment works by building enough trust with the protectors that the client — guided by the Self, a stable compassionate witnessing presence — can approach the exile and offer it what it never received: acknowledgment, and the knowledge that the trauma is over. This “unburdening” allows the frozen material to be integrated and the protectors to stand down (Schwartz & Sweezy, 2020). The felt safety of the Self state is thought to reduce amygdala reactivity sufficiently to widen the window of tolerance and permit memory reconsolidation.
MDMA-assisted therapy works through a different but complementary mechanism. MDMA produces a significant release of serotonin, oxytocin, and dopamine, which reduces amygdala reactivity to threat cues and enhances feelings of trust and interpersonal safety (Mithoefer et al., 2018). This pharmacologically widens the window of tolerance, allowing clients to approach traumatic material with a degree of psychological safety that would otherwise be very difficult to sustain. There is also evidence of increased neuroplasticity in the MDMA state, which may facilitate the reconsolidation of traumatic memories (Mitchell et al., 2021).
What all four approaches share is a common underlying logic: traumatic material cannot be processed through insight or willpower alone, because the obstacle is neurobiological, not cognitive. Each modality creates the specific conditions under which the nervous system can do what it has been trying to do since the trauma occurred — integrate the experience and recognize it as past. In every case, the work must stay within the window of tolerance, and in every case, what is being restored is the nervous system’s capacity to recognize that the threat is over.
References
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Lanius, R. A., Vermetten, E., Loewenstein, R. J., Brand, B., Schmahl, C., Bremner, J. D., & Spiegel, D. (2010). Emotion modulation in PTSD: Clinical and neurobiological evidence for a dissociative subtype. American Journal of Psychiatry, 167(6), 640–647.
Levine, P. A. (1997). Waking the Tiger: Healing Trauma. North Atlantic Books.
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Mitchell, J. M., Bogenschutz, M., Lilienstein, A., Harrison, C., Kleiman, S., Parker-Guilbert, K., … Doblin, R. (2021). MDMA-assisted therapy for severe PTSD. Nature Medicine, 27, 1025–1033.
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Schwartz, R. C., & Sweezy, M. (2020). Internal Family Systems Therapy (2nd ed.). Guilford Press.
Shapiro, F. (2018). Eye Movement Desensitization and Reprocessing (EMDR) Therapy: Basic Principles, Protocols, and Procedures (3rd ed.). Guilford Press.
Shin, L. M., Rauch, S. L., & Pitman, R. K. (2006). Amygdala, medial prefrontal cortex, and hippocampal function in PTSD. Annals of the New York Academy of Sciences, 1071, 67–79.
Siegel, D. J. (1999). The Developing Mind: How Relationships and the Brain Interact to Shape Who We Are. Guilford Press.
Stickgold, R. (2002). EMDR: A putative neurobiological mechanism of action. Journal of Clinical Psychology, 58(1), 61–75.van der Kolk, B. A. (1994). The body keeps the score: Memory and the evolving psychobiology of posttraumatic stress. Harvard Review of Psychiatry, 1(5), 253–265.
