Trauma and the Brain

If you've ever wondered why you can't just "get over" something, this page is for you. It explains, in plain language, what trauma does to the brain and body, why the effects can last, and how EMDR therapy is thought to help. It's for education. It isn't a substitute for care from a professional.

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An illustration of a glowing brain inside a translucent head, over a lake at sunset

Your built-in alarm system

Your brain has a threat-detection system that works faster than thought. When something looks dangerous, a small structure called the amygdala sends a distress signal to the hypothalamus, which acts like a command centre. Harvard Health describes what happens next: the sympathetic nervous system, the body's "gas pedal," floods you with adrenaline. Your heart races, your breathing quickens and your muscles get ready to fight or run.

If the threat continues, a second system called the HPA axis releases cortisol to keep you on high alert. When the danger passes, the parasympathetic nervous system, the "brake," calms everything down.

This system is a gift. It's why people survive car crashes, fires and assaults. The problem is what happens when it doesn't switch off.

Fight, flight, freeze and fawn

The alarm has more than one setting:

  • Fight: anger, irritability, the urge to push back
  • Flight: anxiety, restlessness, the urge to get away
  • Freeze: going still, numb or blank, feeling unable to move or speak
  • Fawn: appeasing, people-pleasing, keeping everyone calm at your own expense

None of these are choices. Your nervous system picks whichever one is most likely to keep you alive in that moment. Many people feel ashamed that they froze. Freezing is one of the oldest survival responses there is.

What trauma does to memory

Ordinary memories get filed. You know they happened in the past, you can tell the story in order, and the feelings fade over time.

Traumatic memories can be stored differently. The EMDR International Association's Adaptive Information Processing model describes how an experience that overwhelms you at the time can get "stuck," linked to the original images, emotions, beliefs and body sensations. When something in the present resembles it, even faintly, the memory doesn't feel like the past. It feels like now. As EMDRIA puts it, "the past is present."

That's why a smell, a tone of voice or a certain time of year can bring back the racing heart and the sense of danger, long after the event.

Why the effects can last

When the alarm keeps firing, your body stays in a stress state. Harvard Health links long-term stress to high blood pressure, anxiety, depression, sleep problems and more. Day to day, it can look like:

  • feeling on guard, jumpy or unable to relax
  • intrusive memories, nightmares or flashbacks
  • avoiding reminders, places or people
  • trouble concentrating and remembering
  • feeling numb, detached or unreal (see dissociation)
  • beliefs like "I'm not safe," "it was my fault" or "I'm powerless"

In this video, Kyle explains the "anxiety alarm" and what helps quiet it.

The window of tolerance

Psychiatrist Dan Siegel described a "window of tolerance": the zone where you can feel things, think clearly and stay connected to others. Above the window is hyperarousal, with panic, irritability and impulsiveness. Below it is hypoarousal, with numbness, shutdown and dissociation.

Trauma can narrow the window, so it takes less to push you out of it, and you may swing between the two. Much of trauma therapy, including the preparation for EMDR, is about widening that window: learning to notice where you are and having ways to come back.

How EMDR is thought to help

EMDR asks you to briefly hold a piece of a memory in mind while following a back-and-forth movement, usually your eyes tracking your therapist's hand or a moving dot on screen, or alternating taps or tones. Over short sets, the memory tends to lose its vividness and its emotional charge, and more helpful thoughts start to take its place.

Researchers are still working out exactly why. A 2018 systematic review in Frontiers in Psychology looked at 87 studies and found the strongest support for the working-memory idea: holding a memory and tracking movement at the same time competes for limited mental resources, and the memory gets stored again in a less intense form. Other lines of research point to a calming, "orienting" response in the body, similarities with REM sleep, and measurable changes in brain activity after successful treatment. The authors were clear that this research "is still in its infancy," even though the therapy itself is well established.

What is well established is that EMDR works for PTSD. It's recommended in international guidelines, including NICE in the UK and the World Health Organization. You can read more on our What is EMDR therapy page.

In this video, Kyle explains why EMDR works.

What EMDR treatment can address

Because EMDR targets the stored memories that keep the alarm firing, it's used for a wide range of trauma-related difficulties, including:

Calming the alarm at home

You can start working with your nervous system now. Our free resources page has short guided practices from Kyle's YouTube channel, Calm with Kyle, including grounding, a vagus nerve exercise and the butterfly hug. They aren't therapy, but many people find them useful between sessions, or while deciding whether to start.

When to get support

Reactions in the first weeks after something terrible are normal, and many people recover on their own. If the alarm is still firing months later, or it's affecting your sleep, work, relationships or health, therapy can help. KP Psychological offers online trauma therapy, with EMDR at the centre of our work, for adults across Alberta.

Book a free 15-minute consultation

Written by Kyle Poon, M.Ed., R.Psych, EMDRIA Approved Trainer and Consultant · Reviewed September 2026

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