How Does EMDR Therapy Work? Understanding Bilateral Stimulation, Trauma & the Brain
If you’ve been researching EMDR therapy in San Diego, you may have come across videos or articles showing someone following a therapist’s fingers back and forth with their eyes. You may have wondered, “What exactly is that doing? How can moving my eyes help me heal from trauma?”
It’s a great question—and one that researchers are still working to fully answer.
We know that EMDR (Eye Movement Desensitization and Reprocessing) is an effective treatment for PTSD and trauma-related symptoms. Research has also found that bilateral stimulation—the alternating eye movements, sounds, or taps used during EMDR—appears to play an important role in the process. However, scientists don't yet have one definitive explanation for exactly how bilateral stimulation works (Rydberg et al., 2024; Wright et al., 2024).
As a trauma therapist in San Diego, I think it’s important to explain what we know, what we believe may be happening, and what remains a question for researchers.
What is Bilateral Stimulation in EMDR?
Bilateral stimulation, often abbreviated as BLS, refers to alternating stimulation from one side of the body to the other.
During EMDR, this might involve:
Following a light or my fingers with your eyes from side to side
Listening to alternating sounds through headphones
Feeling alternating taps or other tactile stimulation
You may have seen an EMDR light bar in a therapist's office. The light moves back and forth, giving your eyes something to follow while you focus briefly on a traumatic memory, thought, emotion, or body sensation.
But here's something important to understand:
The eye movements aren't the entire treatment.
EMDR is a comprehensive psychotherapy approach that includes preparation, identifying treatment targets, developing resources and coping skills, processing memories, and integrating more adaptive information. Current research on EMDR mechanisms emphasizes that bilateral stimulation alone cannot explain the full effects of EMDR therapy (Rydberg et al., 2024).
The Adaptive Information Processing Model: How EMDR Understands Trauma
One of the foundational concepts behind EMDR is the Adaptive Information Processing (AIP) model.
The AIP model proposes that our brains have a natural capacity to process experiences and integrate them with other information we've learned throughout our lives.
Most of the time, when something difficult happens, we eventually incorporate that experience into our understanding of ourselves and the world.
For example:
“That was a frightening experience, but it's over now. I'm safe.”
The memory doesn't disappear. You can remember what happened, but you aren't necessarily overwhelmed by it every time you think about it.
Traumatic experiences can sometimes be different.
When an experience is overwhelming, frightening, or occurs when we don't have the resources to adequately process it, aspects of the experience may remain connected to intense emotions, physical sensations, negative beliefs, or vivid images.
You may logically know:
“That happened years ago.”
But your body may respond as though:
“It's happening right now.”
This can help explain why someone who has experienced trauma might continue to experience panic attacks, nightmares, anxiety, avoidance, shame, or intense emotional reactions long after the original event has ended.
The AIP model provides a framework for understanding these experiences and for conceptualizing how EMDR may help facilitate more adaptive processing. A 2024 review found that several newer theoretical models may complement and expand our understanding of AIP, while also emphasizing that EMDR's effects cannot be explained by bilateral stimulation alone (Rydberg et al., 2024).
So, How Does Bilateral Stimulation Actually Work?
This is where things get really interesting.
Researchers have proposed several possible explanations for the effects of bilateral stimulation. We don't yet know that any single one is the answer, and it's possible that several mechanisms are working together.
1. Bilateral Stimulation May Engage Working Memory
One of the most researched explanations is called the working-memory hypothesis.
Working memory is the mental system that allows us to temporarily hold and manipulate information.
When you're remembering something traumatic, you're using some of your working-memory capacity to hold the memory in mind.
At the same time, you're following my fingers or a light moving back and forth.
Those two tasks compete for some of the same limited cognitive resources.
Research examining this theory has found that recalling distressing memories while simultaneously performing a secondary task can reduce the vividness and emotional intensity of those memories. A systematic review of 11 studies found evidence supporting the working-memory explanation, although the authors also noted limitations, including evidence that some effects may not persist over longer follow-up periods (Houben et al., 2022).
In everyday language, you might think of it this way:
You're remembering what happened while your brain is also paying attention to something happening in the present.
Over time, the memory may become less vivid and less emotionally overwhelming.
This may help explain why a client can eventually say:
“I still remember what happened, but it doesn't affect me the way it used to.”
2. Bilateral Stimulation May Help You Stay Connected to the Present
Another proposed explanation involves attention and the orienting response.
When something changes in our environment, our attention naturally shifts toward it.
During EMDR, you're moving your attention between the memory and the bilateral stimulation.
In a sense, you're doing something like:
Remembering → noticing the present → remembering → noticing the present.
You're accessing something that happened in the past while simultaneously experiencing the fact that you are sitting in a therapy office right now.
For someone whose nervous system has learned “I'm not safe,” this repeated experience may help create a distinction between the past and the present.
The traumatic event happened.
But it isn't happening now.
Research into the mechanisms of EMDR is increasingly examining attention, memory, predictive processing, and other potential explanations for these effects (Rydberg et al., 2024).
3. Bilateral Stimulation May Influence Physiological Arousal
Trauma isn't just something that happens in your thoughts.
It can affect your entire nervous system.
You might notice:
Your heart racing
Tightness in your chest
Sweaty palms
A lump in your throat
Muscle tension
Nausea
Dizziness
Tingling
Difficulty breathing
A feeling that something terrible is about to happen
Research is beginning to explore how bilateral stimulation may influence physiological arousal and brain activity during memory processing.
This research is promising, but it is still developing. It's more accurate to say that BLS may influence systems involved in attention, emotional processing, and physiological arousal than to claim that we have completely mapped out what happens in the brain during EMDR. For example, a 2025 study found that both visual and tactile bilateral stimulation were associated with changes in frontal EEG activity and reductions in peripheral physiological activation, although the authors emphasized that the neurophysiological mechanisms of BLS remain poorly understood (Stingl et al., 2025).
4. Could EMDR Involve Memory Reconsolidation?
Another fascinating area of research involves something called memory reconsolidation.
Very simply, when we retrieve an established memory, that memory may temporarily become more malleable before being stored again.
This has led researchers to investigate whether therapeutic memory retrieval might create an opportunity for an old emotional memory to be updated with new information.
This concept is particularly interesting when thinking about trauma.
Imagine that your nervous system learned:
“I'm helpless.”
During therapy, you may remember the experience while simultaneously experiencing something very different:
“I'm an adult now.”
“I'm safe.”
“I survived.”
“I have choices now.”
The memory remains part of your history, but its meaning and emotional impact can change.
Memory reconsolidation is one possible explanation being explored in EMDR research, but it would be premature to say that EMDR has been definitively proven to work through this mechanism (Ecker et al., 2024).
And that's an important distinction.
Does EMDR Work Because It Activates Both Sides of the Brain?
You may have heard someone explain EMDR by saying:
“The eye movements make the left and right sides of your brain communicate.”
It's an appealing explanation—but it's not an established scientific explanation for how EMDR works.
Similarly, you may have heard that EMDR works because the eye movements mimic REM sleep.
The relationship between eye movements, attention, memory, and REM sleep is interesting and has been investigated, but neither explanation should be presented as settled science.
The current research is much more nuanced.
Researchers are considering several possible mechanisms—including working memory, attention, physiological arousal, memory processing, and predictive processing—and these theories may eventually help us better understand how EMDR works (Rydberg et al., 2024).
What Does This Mean for Someone Considering EMDR Therapy?
If you're looking for an EMDR therapist in San Diego, you don't necessarily need to understand the neuroscience before getting started.
What is important to know is that EMDR isn't simply about moving your eyes back and forth.
It's a structured psychotherapy approach designed to help you safely process distressing experiences while developing greater access to adaptive information and present-day resources.
And you don't have to start by diving into the most painful memory you've ever experienced.
In trauma therapy, preparation and safety are important parts of the process. Depending on your circumstances and goals, therapy may begin with learning grounding techniques, developing resources, understanding your nervous system, and building your ability to tolerate difficult emotions.
Your therapy should meet you where you are.
EMDR Isn't About Erasing Your Memories
One of the biggest misconceptions about trauma therapy is that healing means forgetting what happened.
That's not the goal.
You may always remember what happened.
The hope is that you can eventually remember it without feeling like you're back there.
Instead of:
“I'm trapped.”
You may begin to recognize:
“I'm here.”
Instead of:
“I'm not safe.”
You may begin to experience:
“I'm safe now.”
Instead of:
“Something is wrong with me.”
You may begin to understand:
“My reactions make sense given what I've experienced.”
That shift can be incredibly meaningful.
Finding a Trauma Therapist in San Diego Who Understands Your Needs
If you're looking for a Trauma Therapist in San Diego, it's important to consider more than whether a therapist lists "trauma" on their website.
Ask about their training and experience.
You might consider asking:
What training have you received in trauma therapy?
Are you trained in EMDR?
How do you approach trauma treatment?
What happens during the first few sessions?
Do you begin trauma processing right away?
How do you help clients develop coping and grounding skills?
How do you make sure clients feel safe during trauma processing?
Credentials and specialized training matter—but so does the relationship you develop with your therapist.
You deserve to work with someone who listens to you, respects your pace, and collaborates with you throughout the process.
Chula Vista Counseling for Trauma, Anxiety & PTSD
If you're looking for a Chula Vista therapist who treats trauma, PTSD, anxiety, or other concerns related to difficult life experiences, therapy can provide a space to better understand what you're experiencing and develop tools for moving forward.
As a trauma-informed, person-centered Licensed Marriage & Family Therapist in Chula Vista, I work primarily with adults who are struggling with trauma, anxiety, depression, PTSD, and grief and loss.
I incorporate EMDR and other trauma-focused interventions into therapy when appropriate, always taking into consideration your goals, preferences, readiness, and individual circumstances.
I believe that your symptoms aren't evidence that something is wrong with you.
Often, they are understandable responses to what you've experienced.
And with the right conditions and support, change is possible.
Ready to Learn More About EMDR Therapy in San Diego?
If you've been considering EMDR but aren't sure whether it's right for you, you don't have to figure it out alone.
I offer in-person therapy in Chula Vista as well as online counseling for California residents. If you'd like to learn more about how EMDR or trauma-focused therapy might fit your needs, I invite you to schedule a complimentary 15-minute consultation.
You don't have to be ready to process everything. You just have to be ready to take the next step.
FAQs About EMDR Therapy
What is EMDR therapy?
EMDR, or Eye Movement Desensitization and Reprocessing, is a structured psychotherapy approach originally developed to help people process distressing memories and trauma. It incorporates bilateral stimulation along with other therapeutic components to help clients process experiences that continue to cause emotional or physiological distress.
How does EMDR therapy work?
Researchers are still studying exactly how EMDR works. Current theories include working-memory taxation, changes in attention and physiological arousal, and possible processes related to memory reconsolidation. The Adaptive Information Processing model provides the primary theoretical framework used by EMDR clinicians, while newer research suggests that several mechanisms may contribute to therapeutic change (Houben et al., 2022; Rydberg et al., 2024).
What is bilateral stimulation?
Bilateral stimulation involves alternating stimulation from one side of the body to the other. In EMDR, this may involve following a therapist's fingers or a light with your eyes, listening to alternating sounds, or experiencing alternating taps.
Does EMDR actually work for PTSD?
Research supports EMDR as an effective treatment for PTSD. A 2024 systematic review and individual participant data meta-analysis examined randomized controlled trials involving adults with PTSD and found EMDR to be effective in reducing PTSD symptoms, with outcomes comparable to other psychological treatments in many analyses (Wright et al., 2024). A more recent systematic review and meta-analysis also found EMDR to be associated with significant reductions in PTSD symptoms compared with control conditions, while noting that outcomes varied depending on the type of comparison treatment (Wright et al., 2026).
Do I have to talk about my trauma in detail during EMDR?
Not necessarily. EMDR treatment is individualized, and your therapist should consider your readiness, goals, current level of stability, and ability to tolerate distress. Preparation and developing appropriate coping and grounding skills can be an important part of therapy before beginning memory processing.
Does EMDR erase traumatic memories?
No. The goal of EMDR is not to erase memories. Instead, therapy aims to help distressing memories become less emotionally and physiologically overwhelming so that you can remember what happened without feeling as though you are experiencing it again in the present.
Is EMDR only for PTSD?
EMDR was developed as a treatment for trauma and PTSD and has the strongest research base for PTSD. Clinicians also use EMDR and trauma-focused approaches with other concerns, including anxiety, panic, grief, and distress associated with difficult life experiences. Whether EMDR is appropriate depends on the individual client's circumstances and treatment goals.
Do the eye movements have to be used for EMDR to work?
EMDR can incorporate different forms of bilateral stimulation, including visual, auditory, and tactile stimulation. Research continues to investigate whether different forms of stimulation work through the same or different mechanisms. The broader EMDR treatment protocol involves substantially more than the bilateral stimulation component alone (Rydberg et al., 2024; Stingl et al., 2025).
How do I find an EMDR therapist in San Diego?
When looking for an EMDR therapist in San Diego, consider the therapist's professional license, specialized EMDR training, experience treating your particular concerns, therapeutic approach, and whether you feel comfortable with them. It's completely appropriate to ask a potential therapist about their training and experience before beginning therapy.
Can I receive EMDR therapy online in California?
Yes! EMDR can be adapted for telehealth when clinically appropriate. If you're considering online EMDR, discuss whether virtual treatment is appropriate for your circumstances with a qualified therapist. I offer online counseling to California residents as well as in-person therapy in Chula Vista.
References
Ecker, B., Ticic, R., & Hulley, L. (2024). Eye-movement desensitization and reprocessing (EMDR). In B. Ecker, R. Ticic, & L. Hulley, Unlocking the emotional brain: Memory reconsolidation and the psychotherapy of transformational change. Routledge. https://doi.org/10.4324/9781003231431
Houben, S. T. L., Otgaar, H., Roelofs, J., & Merckelbach, H. (2022). Can working memory account for EMDR efficacy in PTSD? BMC Psychology, 10, Article 239. https://doi.org/10.1186/s40359-022-00951-0
Rydberg, J. A., Virgitti, L., & Tarquinio, C. (2024). Bolstering the adaptive information processing model: A narrative review. Frontiers in Psychiatry, 15, 1374274. https://doi.org/10.3389/fpsyt.2024.1374274
Stingl, M., Schäflein, E., Spieler, D., Henn, M., Hanewald, B., & Sack, M. (2025). Bilateral stimulation: Differential effects in EEG and peripheral physiology. BJPsych Open, 11(6), e278. https://doi.org/10.1192/bjo.2025.10887
Wright, S. L., Karyotaki, E., Cuijpers, P., Bisson, J., Papola, D., Witteveen, A., Suliman, S., Spies, G., Ahmadi, K., Capezzani, L., Carletto, S., Karatzias, T., Kullack, C., Laugharne, J., Lee, C. W., Nijdam, M. J., Olff, M., Ostacoli, L., Seedat, S., & Sijbrandij, M. (2024). EMDR v. other psychological therapies for PTSD: A systematic review and individual participant data meta-analysis. Psychological Medicine, 54(8), 1580–1588. https://doi.org/10.1017/S0033291723003446
Wright, S. L., et al. (2026). Efficacy of eye movement desensitization and reprocessing for posttraumatic stress disorder: A systematic review and meta-analysis of randomized controlled trials comparing passive and active control conditions. [Journal information pending final publication details].
