Can Bilateral Stimulation Calm the Nervous System?
“Bilateral stimulation calms the nervous system.”
You will hear this everywhere.
Sometimes it is used to explain EMDR.
Sometimes ART.
Sometimes tapping, alternating sounds, walking, or even listening to music that moves from one ear to another.
And there is a reason the explanation feels convincing.
People sometimes do notice their bodies becoming calmer during eye-movement-based trauma therapy.
Heart rate may slow.
Breathing may change.
Physical tension may decrease.
A memory that initially felt intensely activating may begin to feel more distant.
But scientifically, the statement:
“Bilateral stimulation calms the nervous system”
is too broad.
There is evidence that eye movements during EMDR are associated with measurable physiological changes.
But those changes do not look like a simple relaxation switch.
What does “the nervous system” mean?
This phrase gets used loosely.
The nervous system includes the brain, spinal cord, peripheral nerves, and autonomic processes involved in functions such as:
heart rate,
breathing,
digestion,
sweating,
pupil response,
blood pressure,
and readiness for action.
When people say they want to “regulate the nervous system,” they usually mean something more specific:
They want to feel less physiologically activated.
Less tense.
Less panicked.
Less braced.
More able to think.
More able to remain present.
That is a reasonable goal.
But it is not the same as flipping a single neurological switch.
What is the autonomic nervous system?
The autonomic nervous system helps regulate processes that happen largely outside conscious control.
It includes sympathetic and parasympathetic activity.
The sympathetic nervous system is often associated with mobilization and increased arousal.
The parasympathetic nervous system contributes to processes involved in rest, digestion, recovery, and regulation.
These systems are not simply:
“bad stress system”
versus
“good calm system.”
They work together continuously.
Healthy regulation involves flexibility—not permanent relaxation.
Trauma can affect physiological arousal
Trauma-related responses can involve:
rapid heart rate,
shallow breathing,
sweating,
muscle tension,
startle,
freezing,
nausea,
or intense bodily alertness.
A reminder of the trauma can produce these responses even when the person consciously knows they are safe.
That is one reason people are interested in whether eye movements or bilateral stimulation alter autonomic arousal.
What has EMDR research found?
Several small psychophysiological studies have measured what happens in the body during EMDR.
Researchers have observed changes including:
decreases in heart rate,
changes in heart-rate variability,
reductions in skin conductance,
changes in breathing,
and changes in fingertip temperature.
A systematic review of proposed EMDR mechanisms concluded that there was reasonable evidence for physiological changes associated with successful EMDR treatment, while emphasizing that the mechanism literature remained too limited for firm conclusions.
So there is a physiological signal worth taking seriously.
But the details matter.
An early study found a relaxation-like pattern
A 1996 randomized study compared EMDR with two control conditions in 18 people distressed by a traumatic memory.
During EMDR, researchers observed:
slower heart rate,
lower galvanic skin response,
higher fingertip temperature,
changes in respiration,
and an overall decrease in systolic blood pressure.
The authors described the pattern as consistent with a relaxation response.
That sounds like strong support for the “calms the nervous system” explanation.
But that was a very small study.
Later findings have made the picture more complicated.
Another study found autonomic shifts during eye movements
A study of people with PTSD measured physiological changes during EMDR eye movements.
Researchers found decreases in:
heart rate,
skin conductance,
and a heart-rate-variability measure associated with autonomic balance.
Fingertip temperature also increased.
The authors interpreted the findings as indicating reduced sympathetic activity and increased cholinergic influences during eye movements.
Again, that suggests eye movements may be associated with physiological de-arousal.
But it still does not mean every eye-movement set simply relaxes the body.
Eye movements can initially increase orienting too
This is where the story gets more interesting.
Another experimental study compared EMDR with and without eye movements.
When eye movements began, heart rate decreased and skin conductance decreased across sets, while heart-rate variability and respiration changed.
But researchers also found more orienting responses at the beginning of eye-movement exposure.
That means the process may involve:
first orienting,
then habituating,
then de-arousing.
Not simply:
eye movements → instant relaxation.
What is an orienting response?
The orienting response is the nervous system's automatic reaction to something novel or changing.
You hear a sound behind you.
Your attention shifts.
Something moves in your peripheral vision.
You look.
The nervous system briefly asks:
What is that?
A moving visual target naturally captures attention.
Some EMDR researchers have proposed that eye movements repeatedly trigger this orienting response.
If the stimulus continues and nothing dangerous happens, the response may gradually habituate.
The system learns:
This is not a threat.
That may contribute to physiological settling.
So bilateral stimulation might activate before it calms
Exactly.
This is one reason the word “calming” can be misleading.
An eye-movement set may initially produce:
attention,
orienting,
and physiological change.
Then the response may decrease.
A small clinical study in Timor-Leste found that EMDR sessions were associated with overall physiological de-arousal, but individual eye-movement sets produced an immediate pattern consistent with an orienting response that then habituated.
That is much more nuanced than saying bilateral stimulation simply activates the parasympathetic nervous system.
What happens across a session?
Some studies suggest physiological arousal can decrease across the course of trauma processing.
One preliminary investigation tracked 55 EMDR sessions from 10 people with PTSD.
Researchers found changes suggesting immediate de-arousal when stimulation began, more complex physiological activation during continued stimulation, and an overall decrease in psychophysiological activity across the session.
In other words:
the nervous system may move.
It may activate.
Settle.
Activate again.
Then gradually become less reactive.
That is very different from simply inducing relaxation.
And newer research adds an important caution
A 2025 randomized controlled study compared eye-movement desensitization with trauma-memory retrieval without eye movements in people with PTSD.
Both conditions reduced several measures of stress reactivity.
The researchers did not find broad specific physiological advantages for adding eye movements, although heart-rate recovery following trauma scripts improved more rapidly in the eye-movement group. Cortisol findings were inconsistent.
That matters.
It suggests some physiological change may come from trauma-memory processing itself—not necessarily bilateral stimulation alone.
So does bilateral stimulation calm the nervous system?
A careful answer would be:
Eye movements used during trauma processing can be associated with changes in autonomic arousal, and several studies have found patterns of physiological de-arousal. But the evidence does not support the simplistic claim that bilateral stimulation reliably or uniquely “switches the nervous system into calm.”
The process appears more dynamic.
What about heart rate?
Several studies have reported decreases in heart rate during eye-movement processing.
That can be consistent with reduced arousal.
But heart rate is only one physiological measure.
It is influenced by:
breathing,
movement,
attention,
emotion,
medications,
physical conditioning,
and many other factors.
A lower heart rate does not by itself prove that trauma has been processed.
What about skin conductance?
Skin conductance reflects activity of sweat glands controlled largely by sympathetic nervous-system activity.
Higher skin conductance commonly accompanies physiological arousal.
Several EMDR studies have observed decreases during eye-movement processing.
That suggests physiological activation may diminish.
Again:
useful clue.
Not a complete mechanism.
What about heart-rate variability?
Heart-rate variability, or HRV, measures variation in the intervals between heartbeats.
It is often used in research examining autonomic regulation.
Some EMDR studies have reported changes in HRV during eye-movement sets.
But HRV is complicated.
It should not be reduced to:
“Higher HRV means your nervous system is healed.”
Context matters.
So do breathing, age, health, medication, fitness, and measurement conditions.
Does bilateral stimulation activate the vagus nerve?
This claim is increasingly common online.
The vagus nerve plays an important role in parasympathetic regulation.
But we do not currently have strong evidence showing that bilateral stimulation works primarily by directly “activating the vagus nerve.”
Eye movements may be associated with autonomic changes.
That is not the same thing as proving a direct vagal mechanism.
Those claims should be separated.
Does bilateral stimulation switch you from sympathetic to parasympathetic?
Not in a clean binary way.
Physiology during trauma processing can show both activation and de-activation.
That is not necessarily a problem.
The goal of trauma therapy is not to remain relaxed while avoiding emotional activation.
Some activation may be necessary because the relevant memory needs to become accessible.
The important question is whether the person can experience that activation without becoming overwhelmed—and whether the response changes as processing continues.
“Calm” may not even be the most useful goal
Suppose a client begins a trauma-processing session highly activated.
If the end result is:
“I can think about that memory and stay present,”
that may be much more important than whether they felt completely relaxed during every eye-movement set.
Trauma therapy is not a spa treatment.
The therapeutic goal is usually not relaxation itself.
It is increased flexibility.
Regulation means being able to move
A well-regulated nervous system is not always calm.
It can mobilize when needed.
Settle afterward.
Experience emotion.
Recover.
Respond proportionately.
Regulation is flexibility.
Not flatness.
That matters because describing trauma treatment as “calming the nervous system” can imply that activation itself is pathological.
It is not.
What about bilateral tapping?
Alternating tapping is also used as bilateral stimulation.
But it should not automatically be assumed to have the same cognitive or physiological effects as eye movements.
Research on emotional memory suggests different dual tasks can reduce vividness and emotionality, but the degree to which they tax working memory may differ. A 2020 meta-analysis found that eye movements and other dual tasks both reduced vividness and emotionality in laboratory studies, with eye movements showing a small advantage for vividness.
So:
alternating left-right does not necessarily make every task equivalent.
What about alternating sounds?
Same caution.
Auditory bilateral stimulation may create dual attention.
It may be useful clinically.
But we should not assume that sounds, tapping, and eye movements all work through exactly the same mechanism simply because they alternate.
Different sensory tasks place different demands on the brain.
Does bilaterality itself matter?
That remains an open question.
Research showing that non-eye-movement dual tasks also affect emotional memories suggests the critical ingredient may not simply be left-right alternation.
A larger 2021 meta-analysis of 53 laboratory studies found that dual-task interventions reduced the vividness and emotionality of both negative and positive memories, supporting the broader idea that limited working-memory resources matter.
That pushes us toward a more sophisticated explanation:
the task may change emotional memory partly because it competes for cognitive resources while the memory is active.
Working memory and physiological regulation may both matter
These theories do not have to compete.
One process may alter:
the vividness of the memory.
Another may alter:
attention.
Another:
physiological arousal.
Another:
the meaning of the experience.
Psychotherapy can involve several mechanisms at once.
That is probably more realistic than looking for one master switch.
What about ART?
Accelerated Resolution Therapy, or ART, also uses visually guided eye movements.
Clients often report shifts in body sensations during ART.
A sensation may:
move,
decrease,
change quality,
or disappear.
That is clinically interesting.
But ART-specific physiological mechanism research is much more limited than the EMDR literature.
So I would be cautious about saying:
“ART eye movements directly activate the parasympathetic nervous system.”
We do not currently have enough ART-specific evidence for that statement.
ART may still influence physiological experience
That does not mean nothing is happening.
During ART, clients work simultaneously with:
emotional memory,
visually guided eye movements,
body sensations,
and structured imagery.
Those processes can change subjective arousal.
But we need to distinguish:
what clients experience
from
what physiological research has proven.
Those are not always identical.
Why can body sensations change during processing?
A traumatic memory can activate a physiological response.
If the emotional significance of the memory changes, the associated body response may also change.
For example:
a memory produces chest tightness.
The memory becomes less threatening.
The chest tightness decreases.
That does not necessarily mean the eye movements directly “released trauma from the chest.”
A more cautious explanation is that the nervous system's response to the memory changed.
Trauma is not literally stored in the muscles
This is another phrase worth handling carefully.
Trauma can absolutely produce:
muscle tension,
pain,
autonomic arousal,
and body-based reactions.
But saying trauma is literally “stored in the body” can suggest that trauma exists as a physical substance trapped inside tissue.
Traumatic learning is better understood as involving interconnected systems of:
memory,
emotion,
attention,
physiology,
behavior,
and meaning.
The body participates.
It is not simply a storage container.
What about polyvagal theory?
Polyvagal language is increasingly used to explain trauma and bilateral stimulation.
Terms such as:
ventral vagal,
sympathetic,
and dorsal vagal
have entered mainstream therapy language.
Some aspects of autonomic-state thinking can be clinically useful.
But the broader claims made under the umbrella of polyvagal theory remain scientifically debated.
So I would be cautious about explaining bilateral stimulation as:
“moving someone from dorsal vagal to ventral vagal.”
That statement is much more specific than the evidence for bilateral stimulation allows.
Does feeling calmer prove processing occurred?
No.
A person can relax without processing trauma.
Deep breathing can create relaxation.
So can lying down.
So can music.
Conversely, meaningful trauma processing can occur while the person still feels emotionally activated.
A drop in physiological arousal can be helpful.
But it should not be treated as the sole marker of successful processing.
What matters more?
Clinically, I care about questions such as:
Can the client bring up the memory without becoming overwhelmed?
Does the image feel less intrusive?
Does the body still respond as though the event is happening?
Has shame decreased?
Has avoidance changed?
Can the person encounter reminders with more flexibility?
Do they have more choice?
Those changes tell us much more than whether someone simply felt relaxed during bilateral stimulation.
Can bilateral stimulation help with anxiety?
Possibly, depending on how it is being used.
If anxiety is connected to a vivid memory or feared image, a dual-attention task may reduce that image's vividness or emotionality.
But simply tapping back and forth whenever anxious should not automatically be considered equivalent to EMDR or ART.
A therapy protocol involves:
assessment,
target selection,
timing,
and clinical judgment.
The technique is not the entire treatment.
Is self-administered bilateral stimulation the same as therapy?
No.
Someone can use alternating tapping or other bilateral activities as a grounding or self-soothing strategy if they find them helpful.
But that is different from receiving EMDR or ART.
Therapy involves:
assessment,
preparation,
target selection,
processing,
monitoring,
and integration.
Following a bilateral-stimulation video online is not equivalent to a full trauma-treatment protocol.
Why the language matters
“Calms the nervous system” sounds harmless.
But language shapes expectations.
If someone becomes activated during trauma processing, they may think:
This is not working.
My nervous system should be calm.
That is not necessarily true.
Processing may involve activation followed by change.
A more useful explanation is:
Eye-movement trauma therapies can affect physiological arousal, attention, and emotional memory. The nervous system may become less reactive as processing unfolds, but the process is dynamic rather than simply relaxing.
What does the research support most clearly?
At this point, we can reasonably say:
Eye movements during EMDR are associated with measurable psychophysiological changes in some studies.
Some studies have observed reduced heart rate, skin conductance, and overall physiological arousal during or across treatment.
Eye-movement sets may also initially trigger an orienting response before habituation occurs.
A newer randomized study found that both eye movements and trauma-memory retrieval without eye movements reduced stress reactivity, with only limited physiological advantages specific to eye movements.
And working-memory research suggests bilateral eye movements may simultaneously affect emotional memory itself.
That is much more interesting than a simple “calm button.”
What the research does not justify saying
I would be cautious about telling clients that bilateral stimulation:
“resets the nervous system,”
“activates the vagus nerve,”
“turns off fight-or-flight,”
“balances the hemispheres,”
“moves the body into ventral vagal safety,”
or
“releases trauma stored in the body.”
Those statements either go beyond the evidence or turn complicated processes into misleading biological certainty.
Why I prefer a more precise explanation
I use both ART and EMDR.
What interests me about the eye movements is not whether they provide a catchy explanation.
It is what they may actually be doing.
How do they change attention?
How do they affect working memory?
What happens to physiological arousal?
Why does a body sensation sometimes change?
Why can a traumatic image suddenly feel farther away?
Why does the body stop responding so strongly to something it once treated as danger?
Those are far more interesting questions than:
“How do we hack the nervous system into being calm?”
Working with Laura Geftman, LCSW
I use Accelerated Resolution Therapy and EMDR within a broader trauma-focused practice.
My work may also incorporate IFS, Cognitive Processing Therapy, Prolonged Exposure, CBT, psychodynamic, interpersonal, attachment, and schema therapies depending on the client and clinical question.
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 your body continues to react strongly to a memory or trigger even though you understand intellectually that you are safe, ART, EMDR, or another focused trauma approach may be worth exploring.
The goal is not permanent calm.
It is helping your emotional and physiological responses become more flexible, proportional, and connected to what is happening now.
Suggested Reading
If you are interested in bilateral stimulation, nervous-system responses, ART, EMDR, or trauma processing, these related articles may be helpful:
What Does Research Actually Say About Eye Movements in EMDR?
How Do Eye Movements Work in Accelerated Resolution Therapy?
FAQ
Can bilateral stimulation calm the nervous system?
It may be associated with reduced physiological arousal during trauma processing. Studies of EMDR have reported changes in heart rate, skin conductance, heart-rate variability, breathing, and other autonomic measures. But the process is more complex than simply switching the nervous system into a calm state.
Does bilateral stimulation activate the parasympathetic nervous system?
Some studies have found physiological patterns consistent with reduced sympathetic arousal and increased parasympathetic influence during eye movements. However, the evidence is limited, and autonomic responses during processing can include both activation and de-arousal.
Does bilateral stimulation activate the vagus nerve?
There is not strong evidence establishing direct vagus-nerve activation as the mechanism by which bilateral stimulation works. Autonomic changes have been observed, but that does not prove a specific direct vagal mechanism.
Does EMDR lower heart rate?
Several small studies have observed decreases in heart rate during eye-movement sets or across EMDR sessions.
What is the orienting response in EMDR?
The orienting response is an automatic attentional and physiological reaction to a novel or changing stimulus. Eye movements may initially trigger orienting, followed by habituation and reduced physiological activation.
Is bilateral stimulation just a relaxation technique?
No. Trauma processing can involve both activation and de-arousal. The purpose of bilateral stimulation within EMDR or ART is not simply to relax the client.
Is tapping the same as eye movements?
Not necessarily. Other dual tasks can affect emotional memories, but different tasks may place different demands on working memory. Research does not establish all forms of bilateral stimulation as equivalent.
Does bilateral stimulation release trauma from the body?
That is not a scientifically precise description. Trauma can produce body-based and autonomic responses, and those responses can change during treatment, but trauma is not literally stored as a substance in body tissue.
Does ART calm the nervous system?
Clients may experience changes in physiological and body-based distress during ART, but ART-specific research has not yet established a distinct autonomic mechanism comparable to claims sometimes made about bilateral stimulation.
Is nervous-system regulation the goal of trauma therapy?
Regulation is important, but the goal is not to remain calm all the time. Healthy regulation involves being able to activate when appropriate, recover afterward, tolerate emotion, and respond flexibly rather than being repeatedly overwhelmed by old threat responses.