BRIEF OVERVIEW
UNDERSTANDING EMDR: HOW IT WORKS ON TRAUMATIC MEMORIES
A guide from Creative Mental Health
Why some memories feel different
Think of your brain a little like a factory. All day long, information comes in through your senses — what you are hearing, seeing, and experiencing — and enters a part of the brain called the amygdala. The amygdala is like your control panel. It is where your body’s alert system is based, the part of the brain responsible for recognising danger and switching on your fight-or-flight response. It is also where your here-and-now consciousness lives.
From there, a kind of conveyor belt usually carries your experiences across to another area of the brain called the hippocampus. The hippocampus is your memory library. When a memory arrives there, it gets time-stamped and filed away in its proper place. When you access that memory later, your brain knows it belongs to the past. You are thinking about something that happened, not reliving it.
What happens with trauma
When something deeply traumatic occurs, it can be as though a very large box gets stuck on that conveyor belt. It is too big to pass through, and it sits there in the amygdala — the here-and-now part of the brain — unable to make its way through to the library. Because it never gets time-stamped and filed away, the brain keeps treating it as something that is still happening right now.
This is why trauma can feel so immediate, even years later. Flashbacks, intrusive memories, and sudden waves of emotion are not signs of weakness or of something being “wrong” with you. They are signs of a memory that the brain has not yet been able to process and file away.
A secondary effect can also occur. While that large box is blocking the belt, smaller everyday experiences that would normally move through freely can start to pile up behind it. Ordinary things in daily life begin to feel disproportionately intense — and that makes complete sense once you understand what is happening in the brain.
It is also worth knowing that for some people, a traumatic event from the past may not cause obvious symptoms straight away. Sometimes, months or even years later, something shifts — a life change, a new stressor, accumulated time — and that box becomes a problem. Delayed-onset symptoms are a recognised and documented clinical phenomenon, and they respond just as well to treatment.
What EMDR does
EMDR works by helping the brain complete what it could not do at the time. The aim is to unpack that stuck box, examine what is inside, and then fold everything up neatly so it can travel down the conveyor belt, be time-stamped, and filed away in the library — experienced at last as something that belongs to the past.
To do this, there is a necessary element of revisiting the memory. Both EMDR and trauma-focused CBT involve carefully looking at what is inside the box. The difference is in how EMDR helps the brain process what it finds.
What it feels like in a session
I often describe EMDR processing as like getting on a train. A specific memory — the image that represents the worst moment — is your starting point, your station. The brain then leads. It will take you wherever it needs to go, and I will check in with you along the way. You do not need to narrate or explain what comes up. You simply notice. The brain already knows the route.
The bilateral stimulation — where your eyes follow a moving point back and forth — gently occupies part of the brain’s attention. This appears to help the memory lose its intensity while it is being revisited, so that it can finally be processed and stored properly.
How long does it take?
NICE guidelines recommend that EMDR is typically provided over 8 to 12 sessions, each usually around 60 to 90 minutes.
Is it evidence-based?
Yes. EMDR is recommended by NICE and the World Health Organisation as a first-line treatment for PTSD. Decades of clinical trials confirm that it works — and that it can work even for people who have been carrying their trauma for many years.
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Want to understand the neuroscience and research behind this? Read more below.
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References
National Institute for Health and Care Excellence (2018) Post-traumatic stress disorder. NICE Guideline [NG116]. London: NICE. Available at: www.nice.org.uk/guidance/ng116 (minor changes August 2024).
Shapiro, F. (2018) Eye Movement Desensitization and Reprocessing (EMDR) Therapy: Basic Principles, Protocols, and Procedures. 3rd edn. New York: Guilford Press.
World Health Organization (2013) Guidelines for the Management of Conditions Specifically Related to Stress. Geneva: WHO.
THE RESEARCH — FOR THE CURIOUS READER
This section assumes you have already read the overview above. It picks up where that left off and goes into the science and evidence in more depth.
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The brain science behind the analogy
The factory and conveyor belt picture is a simplification, but it maps onto real neuroscience. The hippocampus plays a central role in encoding episodic and autobiographical memory — giving experiences their time-stamp and their sense of “this happened, it is in the past.” The amygdala drives emotional salience and threat appraisal, operating most powerfully under conditions of fear and overwhelm.
In PTSD, the traumatic memory is understood to remain stored in implicit memory — unintegrated, without context — rather than being processed into the hippocampal network where it would be experienced as a past event (NICE, 2018). This is why flashbacks feel like the present tense. It is not a metaphor: the memory literally has not been filed as past.
The theoretical model: Adaptive Information Processing
The framework underlying EMDR is called the Adaptive Information Processing (AIP) model, developed by Francine Shapiro. The AIP model proposes that highly distressing events can disrupt the brain’s emotional balance, resulting in the consolidation of memories — along with associated cognitions, emotions, and physiological reactions — in a “frozen” state within isolated memory networks that can be activated by a wide variety of everyday triggers (Shapiro, 2018; de Jongh et al., 2024). EMDR works by stimulating the brain’s own innate processing system, helping it resume the integration that was interrupted at the time of the trauma.
Why bilateral stimulation works: what the research says
The bilateral stimulation is the most studied and debated element of EMDR. Several complementary explanations have been proposed.
Working memory theory is the most extensively researched. Working memory has a limited capacity; when two tasks compete for the same resources simultaneously, each receives less. Holding a distressing memory in mind whilst tracking bilateral stimulation is thought to tax this system, reducing the vividness and emotional charge of the memory in real time. A 2022 systematic review found consistent support for this mechanism across both experimental and clinical PTSD studies, concluding that recalling a traumatic memory whilst performing a secondary task shifts attention away from the retrieval process and results in a reduction in vividness and emotionality (Wadji, Martin-Soelch and Camos, 2022).
The REM sleep hypothesis draws on similarities between bilateral eye movements and the neurophysiology of Rapid Eye Movement sleep — during which the brain naturally consolidates and integrates emotionally charged memories. The proposal is that bilateral stimulation produces a brain state functionally similar to REM, facilitating the same integrative process (de Jongh et al., 2024).
Neuroimaging evidence adds a further layer. Studies have shown that successful EMDR treatment is associated with a reduction in amygdala over-activation and an increase in prefrontal cortical engagement — a measurable shift from a threat-response mode to a higher-order processing mode (de Jongh et al., 2024). In simpler terms: the brain stops treating the memory as an emergency and starts treating it as information.
An honest note on mechanism
The precise neurobiological mechanism of EMDR is still being researched and debated. The working memory theory has the strongest experimental support, but it may not fully account for all the effects observed. Some researchers have also noted that EMDR shares certain elements with trauma-focused CBT — including brief imaginal exposure and cognitive restructuring — and that these overlapping components may contribute to outcomes alongside the bilateral stimulation (NICE, 2018).
This is an area of active and productive scientific inquiry, not a question mark over effectiveness. EMDR’s clinical value rests on a robust evidence base independent of which mechanistic theory ultimately prevails.
What the guidelines say
EMDR is recommended as a first-line treatment for PTSD by NICE (NG116), the World Health Organisation, and the American Psychiatric Association. It is one of only two psychological therapies — alongside trauma-focused CBT — given this status in UK national guidance. NICE recommends that EMDR is typically provided over 8 to 12 sessions, each usually 60 to 90 minutes (NICE, 2018).
NICE guidance is also explicit that trauma-focused work requires a trusting, therapeutic, and non-judgmental relationship to be established before and maintained throughout processing. That therapeutic relationship is not incidental to the method — it is the condition under which it becomes possible.
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References
de Jongh, A., Amann, B.L., Maxfield, L., Mevissen, L. and Lee, C.W. (2024) ‘State of the science: Eye movement desensitization and reprocessing (EMDR) therapy’, Journal of Traumatic Stress. doi: 10.1002/jts.23012.
National Institute for Health and Care Excellence (2018) Post-traumatic stress disorder. NICE Guideline [NG116]. London: NICE. Available at: www.nice.org.uk/guidance/ng116 (minor changes August 2024).
Shapiro, F. (2018) Eye Movement Desensitization and Reprocessing (EMDR) Therapy: Basic Principles, Protocols, and Procedures. 3rd edn. New York: Guilford Press.
Wadji, D.L., Martin-Soelch, C. and Camos, V. (2022) ‘Can working memory account for EMDR efficacy in PTSD?’, BMC Psychology, 10(245). doi: 10.1186/s40359-022-00951-0.
World Health Organization (2013) Guidelines for the Management of Conditions Specifically Related to Stress. Geneva: WHO.