How Does EMDR Work? The Leading Scientific Explanations
Eye Movement Desensitization and Reprocessing (EMDR) is an established psychological treatment with particularly strong research support for Post-Traumatic Stress Disorder (PTSD). Research shows that EMDR can reduce PTSD symptoms, but exactly how it produces those changes is still being studied.
That is not unusual in psychotherapy. A treatment can have evidence showing that it works even when researchers have not completely settled the mechanisms responsible for its effects.
In EMDR, a person brings aspects of a distressing memory to mind while also engaging in bilateral stimulation, most commonly side-to-side eye movements. Researchers have proposed several explanations for what may be happening during this process.
The leading ideas include the Adaptive Information Processing model, the working-memory explanation, changes in memory vividness and emotional intensity, an orienting response, changes that may occur when memories are retrieved and updated, and broader physiological or neurological processes.
These explanations are not necessarily mutually exclusive. Several may describe different parts of the same process.
The Starting Point: What Happens During EMDR?
EMDR is more than eye movements.
Treatment follows a structured protocol that includes identifying target memories, noticing associated thoughts, emotions, physical sensations, and beliefs, and processing those memories while bilateral stimulation is used.
The UK National Institute for Health and Care Excellence (NICE) describes EMDR as a phased treatment that includes identifying and treating target memories and using repeated bilateral stimulation—normally eye movements, although taps or tones may also be used—until those memories are no longer distressing.
The US Department of Veterans Affairs (VA) National Center for PTSD similarly describes EMDR as involving attention to an upsetting memory while simultaneously attending to a back-and-forth movement or sound.
The scientific question is what this combination of memory recall and divided attention does to the memory and the emotional response associated with it.
The Adaptive Information Processing Model
The traditional theoretical framework for EMDR is called the Adaptive Information Processing (AIP) model.
The model proposes that psychological difficulties can sometimes persist when distressing experiences are not fully integrated into broader memory networks. Instead, aspects of an experience may remain connected with the thoughts, emotions, physical sensations, and beliefs that were present when the event occurred.
According to the model, reminders in the present can activate those inadequately processed memories and their associated reactions.
EMDR is proposed to help those memories become more adaptively processed and integrated, so that the event can still be remembered without producing the same level of distress or the same negative meaning in the present.
A 2018 systematic review of proposed EMDR mechanisms described the AIP model as the theoretical framework that guides EMDR treatment.
The review also emphasized that research had not established one definitive biological or psychological mechanism explaining the entire treatment. (PubMed Central (PMC))
A 2024 review of the AIP model similarly noted that researchers have proposed several complementary explanations for EMDR and that treatment effects likely need to be understood in relation to the complete therapy rather than bilateral stimulation alone. (PubMed Central (PMC))
The AIP model therefore provides an overall explanation of what EMDR is intended to accomplish, while other theories try to explain more specifically what may be happening during memory processing.
The Working-Memory Explanation
Among the most researched explanations for EMDR's eye movements is the working-memory hypothesis.
Working memory is the limited mental system we use to temporarily hold and manipulate information.
For example, keeping an image in mind while simultaneously performing another attention-demanding task requires both activities to draw on a limited pool of mental resources.
The working-memory explanation proposes that something similar happens during EMDR.
A person recalls a distressing memory while also following moving fingers or another bilateral stimulus. Because both activities require mental resources, the memory may become harder to hold in exactly the same vivid and emotionally intense form.
Researchers have tested this idea by asking people to recall unpleasant memories while performing eye movements or another demanding task.
A 2022 systematic review found that recalling traumatic material while performing a secondary task generally reduced the vividness and emotional intensity of the recalled material compared with simply recalling it without the additional task.
The authors concluded that the findings provided support for the working-memory explanation, while noting that questions remained about how lasting some of these laboratory effects were. (PubMed)
Earlier experimental work similarly found that unpleasant memories became less vivid and emotionally intense when they were recalled while participants made eye movements. (PubMed)
This is currently one of the better-supported explanations for the role of eye movements in EMDR.
Why Might Reducing Vividness Matter?
A traumatic memory does not have to disappear for treatment to help.
Researchers are interested in whether a memory can remain accessible while becoming less vivid, less emotionally charged, or less likely to produce the same immediate reaction.
Experimental studies have repeatedly investigated this possibility.
A meta-analysis examining the contribution of eye movements included clinical EMDR studies as well as laboratory experiments. It found a significant additional effect of eye movements, with particularly strong effects on memory vividness in laboratory studies. (PubMed)
Another experimental study found that recalling memories while making eye movements produced changes in their vividness and emotionality that were still detectable 24 hours later. (PubMed)
More recent clinical research has also tested whether changes in memory qualities help explain improvement.
A 2024 randomized controlled trial involving 155 people with childhood-related PTSD compared EMDR with imagery rescripting. The researchers specifically examined whether changes in memory vividness and distress might help explain treatment effects.
Their findings supported the idea that changes in the experience of distressing memories may be part of the process through which treatment works. (PubMed)
This does not mean that simply making a memory less vivid explains everything EMDR does. EMDR also addresses beliefs, emotions, physical reactions, and the broader meaning associated with an experience.
Is Divided Attention the Important Part?
The working-memory theory also raises another question: Are eye movements special, or is the important feature that the brain is doing two things at once?
Laboratory research has found that other tasks that compete for working-memory resources can also reduce memory vividness.
For example, early experimental work found reductions in vividness when participants recalled images while performing either eye movements or a spatial tapping task. (PubMed)
This has led researchers to investigate whether different types of bilateral stimulation or other attention-demanding tasks could produce similar effects.
However, this does not establish that every secondary task is equivalent to the eye movements used in EMDR.
A meta-analysis of clinical and laboratory research found an additional effect associated with eye movements, while earlier research reviews had reached less favorable conclusions. (PubMed)
The role of eye movements therefore remains an active research question rather than a completely settled one.
It is examined more closely in Are Eye Movements Necessary for EMDR to Work? and Eye Movements, Tapping or Tones: What Has Research Actually Studied?
The Orienting-Response Explanation
Another theory focuses on the body's orienting response.
The orienting response is an automatic shift in attention that occurs when something new or noticeable appears in the environment. It can involve changes in attention, eye movement, brain activity, and the autonomic nervous system.
Some researchers have proposed that repeated bilateral stimulation may repeatedly trigger an orienting response.
One version of this explanation suggests that the initial response draws attention toward the stimulus and is then followed by a reduction in arousal when the stimulus is recognized as non-threatening.
If this happens while a distressing memory is being recalled, the memory may gradually become associated with a calmer physiological state.
Research examining EMDR mechanisms has found physiological changes during successful treatment that are compatible with some forms of this explanation, although the evidence does not establish the orienting response as the sole mechanism of EMDR. (PubMed Central (PMC))
The working-memory and orienting-response explanations are not necessarily competitors. Eye movements could affect both attention and physiological arousal during memory recall.
Memory Updating and Reconsolidation
Another scientific explanation focuses on what happens when a memory is retrieved.
Memories are not necessarily fixed recordings that remain unchanged each time they are recalled. When a memory is brought back into awareness, it may temporarily become open to updating before it is stored again.
This general process is often discussed in research using the term memory reconsolidation.
Some researchers have proposed that EMDR may take advantage of this window.
A distressing memory is activated, but it is experienced under circumstances that differ from the original event. The person is in the present, attention is divided, and new associations or information may emerge.
When the memory is stored again, its emotional intensity or meaning may therefore be different.
A neurobiological review of EMDR discussed memory reconsolidation alongside working memory, reduced arousal, interhemispheric communication, and other proposed mechanisms.
The authors emphasized that these remain theoretical explanations rather than a single established account of how EMDR works. (PubMed)
Memory updating is attractive as an explanation because it could help account for why people can continue to remember what happened while experiencing the memory differently.
But the precise role of reconsolidation in EMDR remains an area of continuing research.
Does EMDR Simply Work Because It Is Exposure?
Because EMDR involves recalling distressing experiences, researchers have long asked whether its effects could simply be explained by exposure.
Exposure-based treatments also help people engage with traumatic memories or reminders rather than continually avoiding them.
There is clearly some overlap: both approaches involve contact with trauma-related material.
But the procedures differ.
Exposure therapies typically involve sustained or repeated engagement with the memory or trauma-related situations. EMDR generally uses shorter periods of memory activation combined with bilateral stimulation and repeated assessment of what emerges during processing.
Research comparing EMDR with exposure-based treatments has often found that both can produce substantial PTSD improvement. (PubMed)
That does not by itself tell researchers whether they work through exactly the same mechanism.
The working-memory findings, in particular, suggest that performing eye movements or another attention-demanding task while recalling a memory can alter how the memory is experienced in ways that memory recall alone may not.
For treatment comparisons, see EMDR vs Prolonged Exposure Therapy: What Have Studies Found?
What Does Brain Research Tell Us?
Researchers have also used brain imaging and physiological measures to examine what changes during or after EMDR.
Studies have reported changes involving brain networks related to:
memory processing;
emotional regulation;
attention;
threat detection; and
the integration of cognitive and emotional information.
However, this part of the evidence base is less settled than the clinical evidence showing that EMDR can reduce PTSD symptoms.
The 2018 systematic review of mechanisms found preliminary neurobiological evidence but concluded that mechanism research was still at an early stage and that larger, better-controlled studies were needed. (PubMed Central (PMC))
A neurobiological review likewise discussed several possible neural pathways—including working memory, reductions in arousal, memory processes, and brain networks involved in attention and associative learning—without identifying one mechanism as conclusively established. (PubMed)
This research is explored in greater depth in What Does Brain Research Tell Us About EMDR?
Does Bilateral Stimulation Explain All of EMDR?
Probably not.
EMDR is a complete psychotherapy protocol, not simply a set of eye movements.
Treatment includes preparation, identifying target memories, recalling aspects of those memories, noticing thoughts and bodily responses, bilateral stimulation, processing new material that emerges, strengthening more adaptive beliefs, and reassessing the memory.
A review of EMDR theories has emphasized that the treatment's effects should not be reduced to bilateral stimulation alone. (PubMed Central (PMC))
Even if working-memory research explains part of what happens during eye movements, other parts of the treatment may contribute independently or interact with that process.
This is one reason researchers often distinguish between:
How does the complete EMDR treatment work?
and
What specifically do the eye movements or bilateral stimulation contribute?
Those are related, but they are not identical research questions.
Why Isn't There One Accepted Explanation Yet?
Psychological treatments are complex.
They involve memory, attention, emotion, learning, beliefs, physical responses, social interaction, and changes that unfold over time.
A single mechanism may therefore be too simple to explain everything.
The 2018 systematic review identified psychological, psychophysiological, and neurobiological models of EMDR.
It found reasonable empirical support for the working-memory hypothesis and physiological changes associated with successful treatment, while concluding that firm answers about mechanisms still require better research. (PubMed)
The scientific picture is therefore not that researchers have no idea how EMDR might work.
Rather, several plausible mechanisms have evidence behind them, but researchers have not yet established how much each contributes or how they fit together.
What Can We Reasonably Conclude?
The strongest current evidence supports the idea that recalling a distressing memory while performing eye movements or another demanding task can change the way that memory is experienced.
Working-memory research shows fairly consistently that this type of dual task can reduce the vividness and emotional intensity of distressing memories. (PubMed)
Other research suggests that changes in physiological arousal, memory updating, attention, and neural processing may also contribute.
The Adaptive Information Processing model provides EMDR's broader theoretical framework, proposing that treatment helps distressing memories become more adaptively integrated.
None of these explanations has been established as the one complete mechanism.
That distinction is important: the evidence that EMDR can reduce PTSD symptoms is stronger than the evidence explaining exactly why every component of EMDR produces those effects.
For the broader question of whether disagreement about mechanisms changes how a treatment's effectiveness is judged, see Can a Therapy Work Even If Scientists Do Not Fully Agree on Why It Works? The EMDR Mechanism Debate.
Frequently Asked Questions
What is the leading scientific explanation for how EMDR works?
The working-memory explanation currently has substantial experimental support. It proposes that recalling a distressing memory while performing eye movements or another attention-demanding task places competing demands on working memory, which can make the memory less vivid and emotionally intense. (PubMed)
What is the Adaptive Information Processing model?
The Adaptive Information Processing (AIP) model is the main theoretical framework associated with EMDR. It proposes that some psychological symptoms are connected with inadequately processed distressing experiences and that EMDR helps those memories become more adaptively integrated. (PubMed Central (PMC))
Are the eye movements what make EMDR work?
Eye movements appear to contribute to changes in memory vividness and emotionality, and experimental research supports a role for them. However, EMDR is a complete psychological treatment containing several components, so eye movements alone do not explain the entire treatment effect. (PubMed)
Does EMDR erase traumatic memories?
No. The aim is not to erase a memory. Research instead suggests that treatment may change characteristics such as the memory's vividness, emotional intensity, and the reactions associated with recalling it.
Do scientists completely understand how EMDR works?
No. Several mechanisms have scientific support, particularly the working-memory explanation, but researchers have not established one complete mechanism accounting for all EMDR effects. (PubMed)
Conclusion
Scientists have proposed several explanations for how Eye Movement Desensitization and Reprocessing may produce therapeutic change.
The Adaptive Information Processing model provides the broad theoretical framework for EMDR. The working-memory hypothesis has substantial experimental support and may help explain why recalling a distressing memory while making eye movements can reduce its vividness and emotional intensity.
Researchers have also investigated orienting responses, physiological changes, memory updating and reconsolidation, and changes in brain systems involved in attention, memory, and emotional processing.
These explanations may overlap rather than compete.
What research supports most clearly is that EMDR can change the way distressing memories are experienced. Exactly how all of its components combine to produce that change remains an active scientific question.
