How Does Bilateral Stimulation Work in EMDR?
One of the strangest things about EMDR is also the thing everyone notices first:
The eye movements.
A therapist asks you to bring a distressing memory to mind while following movement from side to side with your eyes.
And somehow, for many people, the memory begins to feel different.
Less vivid.
Less immediate.
Less emotionally charged.
Sometimes farther away.
So what exactly is happening?
Why would moving your eyes while remembering something painful change the way the memory feels?
The answer is fascinating.
It is also not completely settled.
EMDR is an evidence-based treatment for post-traumatic stress disorder, but researchers are still studying exactly why its eye-movement component affects emotional memories. A major review of proposed EMDR mechanisms concluded that several psychological, physiological, and neurobiological explanations remain under investigation and that firm conclusions about one definitive mechanism cannot yet be made.
What we can say is that one explanation currently has particularly strong experimental support:
working memory taxation.
First: what is bilateral stimulation?
During EMDR, the client attends to a distressing memory while also engaging in what is commonly called bilateral stimulation.
Most often, this involves following the therapist's fingers or another visual target back and forth with the eyes.
Other forms may include alternating sounds or taps.
But an important distinction gets lost when we simply say “bilateral stimulation.”
The therapeutic ingredient may not be bilaterality itself.
Researchers increasingly study the eye movements as a dual-attention task: your brain is trying to hold a memory in mind while simultaneously doing something else that requires attention and working-memory resources.
That distinction matters.
Because it may help explain why eye movements change the experience of the memory.
What is working memory?
Working memory is the brain's limited-capacity system for temporarily holding and manipulating information.
Think about trying to keep a phone number in mind while someone asks you a question.
Or doing mental arithmetic while trying to remember a grocery list.
There is only so much processing capacity available at once.
Remembering a vivid emotional event also uses working-memory resources.
So does tracking a moving target with your eyes.
The working-memory hypothesis proposes that when you do both simultaneously, the two tasks compete for limited mental resources.
The memory becomes harder to hold with the same vividness and intensity.
Imagine your brain has limited bandwidth
A simple way to think about it is bandwidth.
Imagine recalling a painful memory normally uses most of the available bandwidth.
The picture may be sharp.
The emotions may be intense.
The body sensations may feel immediate.
Now add another demanding task.
Follow this moving target.
Keep the memory in mind.
Notice what happens.
Keep following.
Your brain has to divide its resources.
There is less processing capacity available to maintain the memory in exactly the same vivid, emotionally intense form.
That competition appears to matter.
Experimental studies have repeatedly found that recalling emotional memories while making eye movements can reduce their subsequent vividness and emotionality compared with recalling them without the additional task.
So are the eye movements distracting you?
Sort of—but “distraction” is probably too simplistic.
The working-memory explanation does not suggest that EMDR works because the therapist merely takes your mind off the trauma.
You are actually being asked to keep the distressing material accessible while simultaneously doing something that competes for cognitive resources.
That combination appears important.
Research has found that performing the eye movements while recalling the memory matters more than simply moving the eyes beforehand.
So this is not simply:
“Look over here so you don't think about what happened.”
It is closer to:
“Bring the memory online while giving your brain another sufficiently demanding task.”
Why might the memory feel less vivid afterward?
Memory is not quite like retrieving a video file from a computer.
When we remember something, the memory becomes active.
And when an activated memory is experienced under different conditions, the way it is subsequently represented may change.
Under the working-memory account, recalling a distressing memory while performing eye movements makes the retrieved image temporarily less vivid and emotional.
When you later access that memory, it may retain some of that reduced vividness or emotional intensity.
You still know what happened.
The autobiographical information has not necessarily disappeared.
But the memory may no longer arrive with the same sensory or emotional force.
Does EMDR erase traumatic memories?
No.
EMDR is not memory deletion.
After successful processing, you can generally still remember what happened.
You may still know:
who was there,
what occurred,
what it meant,
and why it mattered.
What may change is the felt quality of remembering.
A client might say:
“I can see it, but it feels farther away.”
“I know it happened, but I don't feel like I'm back there.”
“The picture isn't as sharp.”
“I can think about it without getting flooded.”
That distinction is important.
Trauma treatment is not about making history disappear.
It is about helping the past feel more like the past.
Are eye movements actually necessary?
This is where the science gets especially interesting.
Research suggests that adding eye movements to memory recall can reduce the vividness and emotionality of negative memories, and a frequently cited meta-analysis found an additional effect of eye movements compared with recall alone.
But researchers have also found that other sufficiently demanding tasks can produce similar effects.
Studies have examined:
mental arithmetic,
counting,
complex visuospatial tasks,
playing Tetris,
attentional breathing,
and other tasks that compete for working-memory resources.
Several have also reduced the vividness or emotionality of memories.
That finding supports the idea that at least part of the effect may come from dual-task competition, rather than from horizontal eye movements having a unique ability to unlock trauma.
Does the stimulation actually need to be bilateral?
Maybe not in the way people often assume.
If simply moving stimulation from left to right were the essential mechanism, we would expect the side-to-side pattern itself to be uniquely important.
But working-memory experiments complicate that explanation.
Other cognitive tasks can affect emotional memory too.
Even vertical eye movements and non-eye-movement tasks have produced effects under experimental conditions.
That does not mean bilateral eye movements are irrelevant.
Eye movements appear to be particularly effective at taxing working memory, and their speed and cognitive demand seem to influence the effect.
But it does mean that saying EMDR works because stimulation “activates both hemispheres” is far more confident than the research supports.
Does bilateral stimulation connect the left and right sides of the brain?
You will sometimes hear explanations such as:
“EMDR integrates the left and right hemispheres.”
Or:
“Bilateral stimulation synchronizes both sides of the brain.”
These explanations sound neuroscientific.
But they are not established explanations for EMDR's therapeutic effects.
The brain certainly functions through complex communication among many interconnected networks.
But the idea that alternating stimulation simply switches the left and right hemispheres on and off, or that EMDR works primarily by “balancing” the hemispheres, is an oversimplification.
Current research does not justify reducing EMDR to a left-brain/right-brain story.
What about the orienting response?
Another theory involves the orienting response.
Humans automatically orient toward new or changing stimuli.
A sound.
Movement.
Something entering the visual field.
The eye movements used during EMDR may trigger this orienting response.
Some researchers have proposed that repeated orienting initially produces alertness and then a relaxation response when the stimulus turns out not to represent danger.
That shift might help the person remain connected to the traumatic memory while experiencing less physiological arousal.
The orienting-response explanation remains one of several proposed mechanisms, but it has less consistent support than the working-memory account. Systematic reviews have concluded that multiple mechanisms may contribute rather than one theory explaining everything.
What about the brain's fear system?
Neuroimaging studies have examined changes in brain activity before and after successful EMDR treatment.
Researchers have reported changes involving networks related to emotion, memory, and cortical regulation of limbic responses.
That sounds exciting.
It is.
But there is an important caveat.
Similar brain changes can occur after other effective psychotherapies.
And many EMDR neuroimaging studies have been small or lacked the controls needed to tell us that those changes were specifically caused by eye movements.
A systematic review therefore characterized neurobiological findings as promising but preliminary and cautioned against using them to claim that we know precisely how EMDR works in the brain.
What about memory reconsolidation?
You may also hear EMDR described in terms of memory reconsolidation.
Reconsolidation research begins with an intriguing idea:
When an established memory is reactivated, it may temporarily become more open to modification before it is stored again.
That raises an obvious possibility.
If a traumatic memory is activated during therapy while the person is simultaneously having a new experience—such as noticing safety, experiencing reduced emotional intensity, or processing new information—the subsequently stored memory may be altered.
Reconsolidation is an important area of memory science and may eventually help explain elements of trauma therapy.
But we should be careful here too.
It is plausible that reconsolidation contributes to EMDR.
That is different from proving that EMDR works because of reconsolidation.
At this point, reconsolidation is better described as a possible contributing mechanism than as a settled explanation.
What about REM sleep?
Another popular explanation compares EMDR eye movements to the rapid eye movements that occur during REM sleep.
The basic idea is appealing.
REM sleep is involved in memory and emotional processing.
EMDR also involves rapid eye movements.
Maybe the two processes are related.
But resemblance is not evidence of identical mechanism.
There are hypotheses linking EMDR to sleep-related memory processing, but we do not currently have enough evidence to say that EMDR works by recreating REM sleep while someone is awake.
It is an interesting theory.
It should remain a theory.
What does EMDR's Adaptive Information Processing model say?
EMDR is organized clinically around the Adaptive Information Processing model, often called AIP.
In broad terms, AIP proposes that distress can persist when experiences are stored in ways that remain insufficiently integrated with more adaptive information.
EMDR aims to help those experiences become processed and integrated differently.
AIP is useful as a clinical model.
But a clinical model and a biological mechanism are not the same thing.
AIP helps describe what therapists believe is happening therapeutically.
Working-memory research, neurobiology, psychophysiology, and memory science try to explain how that change may actually be occurring.
Those are related questions, but they should not be confused.
Is working-memory theory proven?
Not completely.
But it currently has substantial experimental support.
A 2024 state-of-the-science review described working-memory taxation as a particularly well-developed explanation and summarized experimental findings showing that combining memory recall with demanding tasks reduces the vividness and emotional intensity of emotional memories.
Researchers have also been able to make predictions from the theory.
For example:
More cognitively demanding eye movements should generally have stronger effects than very slow or minimally demanding movements.
Other demanding tasks should also affect memory.
The task needs to occur while the memory is active.
And excessive cognitive load might interfere with retrieving the memory altogether.
Those predictions have received experimental support.
That makes working-memory theory particularly compelling.
But compelling is not the same thing as final.
Why the amount of cognitive load matters
If working-memory competition contributes to the effect, the task should be demanding enough to compete with the memory.
But not so demanding that you cannot hold the memory in mind at all.
Think of it as a balancing act.
Too little load:
The memory may remain extremely vivid.
Too much load:
You may lose access to the memory entirely.
Somewhere between those extremes may be a more useful level of competition.
Research examining the speed and complexity of eye movements supports the idea that the amount of working-memory taxation influences memory effects.
This is one reason EMDR is more sophisticated than simply “wave your fingers back and forth.”
Is bilateral stimulation the entire treatment?
No.
This is another important misconception.
EMDR is not simply eye movements.
Standard EMDR therapy includes a structured multiphase protocol involving history taking, preparation, assessment, reprocessing, installation, body scan, closure, and reevaluation.
The eye movements occur within that larger clinical process.
So even if we eventually understand exactly what the eye movements contribute, that would not mean we had explained everything about why EMDR therapy works.
Therapeutic relationship matters.
Target selection matters.
Memory activation matters.
Clinical assessment matters.
Preparation matters.
Context matters.
Expectations and meaning matter.
What happens during and between sets matters.
EMDR is a treatment protocol, not simply a neurological trick.
Why can EMDR feel so different from regular talk therapy?
Traditional talk therapy frequently works through language, meaning, reflection, relationship, insight, and new behavior.
EMDR adds another layer.
You are bringing a memory or emotional target online while simultaneously asking the brain to do something else.
That may alter the immediate sensory and emotional experience of remembering.
Instead of only discussing:
“This memory should not have this much power over me,”
you may actually notice:
“This memory does not feel the same anymore.”
That experiential shift is one reason EMDR can feel very different from simply understanding a memory intellectually.
Why can someone understand a trauma and still need processing?
Because knowing and reacting are different systems.
You may know:
“It wasn't my fault.”
And still feel shame.
You may know:
“I am safe now.”
And still feel your stomach drop.
You may know:
“That relationship is over.”
And still react when something reminds you of it.
You may know:
“The procedure ended years ago.”
And still panic in a medical office.
Therapy that incorporates memory processing may help when the intellectual understanding is already there but the emotional or body-based response has not caught up.
How is this relevant to ART?
This gets especially interesting because Accelerated Resolution Therapy, or ART, also uses eye movements.
But ART and EMDR do not use eye movements in exactly the same way.
Both therapies ask the client to engage with emotionally meaningful material while completing visually guided eye movements.
That makes some of the working-memory research relevant to thinking about both approaches.
But ART has its own protocol, pacing, structure, imagery procedures, and therapeutic strategies.
We should not assume that because both therapies involve eye movements, every mechanism is identical.
That deserves its own discussion.
And it will be the next post in this series.
Why I think the uncertainty matters
There is sometimes a temptation in psychotherapy to explain something impressive with neuroscience before the neuroscience is actually established.
“Your amygdala is being reset.”
“Your hemispheres are integrating.”
“Your trauma is being moved from one part of the brain to another.”
“Your brain is being rewired.”
Those statements sound authoritative.
They can also go far beyond the evidence.
I think clients deserve something better.
We can say:
EMDR works.
Eye movements appear to contribute something meaningful.
Working-memory competition has substantial experimental support as one explanation.
Changes in emotional arousal, attention, memory, and possibly reconsolidation may also contribute.
Researchers continue to study what is happening neurobiologically.
And we do not yet have one complete explanation.
That is not a weakness.
That is science.
Working with Laura Geftman, LCSW
I use both Accelerated Resolution Therapy and EMDR as part of a broader trauma-focused practice.
The fact that both therapies use eye movements interests me clinically and scientifically—but I do not consider them interchangeable.
The structure of the therapies differs.
The therapist's role differs.
The way memories are approached differs.
And the way bilateral or eye-movement stimulation is incorporated into the work differs.
Understanding those differences helps us move beyond the simplistic idea that both therapies are merely forms of “eye-movement therapy.”
I offer focused trauma therapy and therapy intensives for adults in Pennsylvania, New Jersey, New York, and Florida.
In-person therapy intensives are available in Ardmore, PA, on the Main Line near Philadelphia.
Virtual therapy may also be available when clinically appropriate.
Interested in ART, EMDR, or focused trauma therapy?
If you understand what happened but continue to feel stuck around a particular memory, image, trigger, body response, or emotional reaction, ART, EMDR, or another focused trauma approach may be worth exploring.
The goal is not to choose a modality because it sounds impressive.
The goal is to determine what kind of work makes sense for you, your history, your target, and where you are now.
Suggested Reading
If you are interested in ART, EMDR, bilateral stimulation, or how trauma processing works, these related articles may be helpful:
FAQ
How does bilateral stimulation work in EMDR?
The exact mechanism is still being studied. One of the strongest current explanations is working-memory taxation: recalling a distressing memory and performing eye movements simultaneously compete for limited working-memory resources, which may make the memory less vivid and emotionally intense.
Why do eye movements make traumatic memories less intense?
Eye movements require attention and working-memory resources. When they occur while a distressing memory is being recalled, fewer cognitive resources may be available to maintain the memory at its original vividness and emotional intensity.
Does bilateral stimulation activate both sides of the brain?
The popular claim that EMDR works simply by “activating both hemispheres” is not an established scientific explanation. The brain is more complex than a left-brain/right-brain model, and current evidence supports more nuanced mechanisms involving attention, working memory, emotional arousal, and memory processing.
Does EMDR rewire the brain?
“Rewiring the brain” is an oversimplified description. Psychotherapy can be associated with changes in brain function, but neuroimaging research does not yet establish a unique neural mechanism explaining exactly how EMDR or its eye movements produce therapeutic change.
Is memory reconsolidation how EMDR works?
Memory reconsolidation may contribute to therapeutic change when an activated memory becomes modified before being stored again, but it has not been established as the single mechanism responsible for EMDR. It remains one plausible area of investigation.
Is bilateral stimulation the same as eye movements?
Eye movements are the best-known form used in EMDR, but alternating sounds or tactile stimulation may also be used. Research suggests that the cognitive demands of the secondary task may matter, and not all forms of stimulation appear to tax working memory equally.
Are the eye movements necessary in EMDR?
Research suggests eye movements can add measurable effects to memory recall, particularly by reducing vividness and emotionality. However, other working-memory tasks can produce similar effects, which suggests that eye movements may work partly because they create a demanding dual-attention task.
Does EMDR work like REM sleep?
There are theories linking EMDR eye movements to processes involved in REM sleep and memory processing, but this mechanism has not been established. Similarity between EMDR eye movements and REM does not mean the processes are biologically identical.
Is EMDR just exposure therapy with eye movements?
EMDR does involve activating distressing memories, which overlaps with mechanisms used in other trauma therapies, but EMDR is a structured multiphase treatment with additional procedures. Researchers continue to debate how much of its effectiveness comes from memory exposure, eye movements, working-memory effects, and other components.
Are ART eye movements doing the same thing as EMDR eye movements?
Possibly in part, but we cannot assume the mechanisms are identical. ART and EMDR both use eye movements while clients engage with emotionally meaningful material, but the protocols use those movements differently. The similarities and differences deserve separate consideration.