What Is Bilateral Stimulation? The Science Behind How EMDR Works

If someone describes EMDR therapy to you as "waving fingers in front of your face," you would be forgiven for thinking it sounds a little strange. That "waving," however, is bilateral stimulation, one of the most researched and effective tools in modern trauma care. This guide explains what it is, how it appears to work, and what actually happens during a session.

Fresh Breath Therapy has offered EMDR at our North Carolina offices for years, and every week our clinicians answer some version of the same question: "How can moving my eyes back and forth possibly help my anxiety?" The short answer is that it does not just involve your eyes. It involves your entire memory system.

Bilateral stimulation, defined simply

Bilateral stimulation (BLS) is a rhythmic sensory input that alternates from one side of the body to the other, used while a client briefly holds a distressing memory in mind. The word "bilateral" simply means "two-sided." That rhythm, whether visual, physical, or auditory, is thought to engage working memory and change how the brain processes the memory.

BLS is not therapy on its own. It is one specific component of Eye Movement Desensitization and Reprocessing (EMDR), a structured, evidence-based therapy for trauma, anxiety, phobias, and grief. For a full introduction to EMDR itself, see our complete guide to EMDR therapy.

The 3 forms of bilateral stimulation

Your therapist can deliver BLS in three main ways. All are equally valid, and your therapist will choose (or let you choose) whichever feels most comfortable.

How it works: 3 leading theories

Researchers agree EMDR works. Multiple randomized controlled trials show it is as effective or more effective than trauma-focused Cognitive Behavioral Therapy for PTSD, and it typically produces results in fewer sessions. What researchers are still refining is exactly why bilateral stimulation is such a key ingredient. Three leading theories help explain what the science currently suggests.

Theory 1: The working memory taxation model

Our working memory (short-term "mental workspace") has limited capacity. When you hold a distressing memory in mind and simultaneously track a moving target, you are asking your brain to do two demanding things at once. Research suggests this dual task weakens the emotional charge of the memory, making it easier to reprocess it in a less overwhelming way.

Theory 2: REM sleep-like brain states

During REM (rapid eye movement) sleep, our eyes move rapidly side to side while the brain naturally consolidates memories. Some researchers propose that BLS induces a similar processing state while you are awake, allowing the brain to file distressing memories the way it normally would during sleep, if only sleep had done the job.

Theory 3: Memory reconsolidation

Every time a memory is accessed, it becomes briefly "editable" before being stored again. BLS may exploit that window, allowing the brain to reconsolidate the memory with new emotional information attached: less threat, more resolution. This is why clients often say the memory is still there afterward, but no longer feels like it is happening in the present.

What a session actually looks like

Here is a rough sketch of the active reprocessing part of a typical EMDR session:

1. Your therapist asks you to bring up a specific memory along with the image, feeling, thought, and body sensation attached to it.
2. You rate your current distress on a 0 to 10 scale, called the SUD (Subjective Units of Distress) scale.
3. You focus on the memory while receiving bilateral stimulation for 20 to 40 seconds.
4. Your therapist pauses and asks, "What comes up now?" You share whatever thoughts, feelings, images, or body sensations arose. No detail required. A single word is fine.
5. Another round of BLS begins. This cycle repeats.
6. Over the session, the memory's charge typically decreases. Your SUD score drops. New insights often surface.

You are fully awake and in control the entire time. If anything feels too intense, you can stop, take a break, or shift focus. Nothing forces you to relive anything you do not want to revisit.

Where BLS fits in the 8-phase EMDR protocol

Bilateral stimulation is not the whole treatment. It is the tool used in Phases 3 through 7 of a structured 8-phase protocol. Skipping the earlier phases (history, preparation, safety-building) is one of the reasons DIY tapping videos on the internet do not produce EMDR's therapeutic effects.

The 8 Phases of EMDR

1. 1
   History taking Your therapist learns your history and identifies the memories to target.
2. 2
   Preparation You learn calming and grounding tools to use throughout treatment.
3. 3
   Assessment You identify the image, thought, feeling, and body sensation tied to the memory.
4. 4
   Desensitization Active reprocessing with bilateral stimulation. The emotional charge of the memory reduces.
5. 5
   Installation A new, adaptive belief (e.g., "I am safe now") is strengthened using BLS.
6. 6
   Body scan You scan your body for any lingering tension tied to the memory.
7. 7
   Closure Your therapist ensures you leave each session in a stable, grounded state.
8. 8
   Reevaluation At the next session, you review progress and identify next targets.

Who bilateral stimulation and EMDR help

EMDR (with bilateral stimulation at its core) has strong research support for:

• Post-traumatic stress disorder (PTSD)
• Childhood and developmental trauma
• Anxiety and panic (see our post on EMDR therapy for anxiety)
• Specific phobias
• Grief and complicated loss
• Performance and test anxiety
• Chronic pain with a psychological component
• Certain forms of depression rooted in past events

Myths and misconceptions

For a fuller look at what to expect at your first appointment, see our guide to your first EMDR session in Cary, NC. It walks through timing, what to wear, and how to prepare mentally.

Frequently asked questions

What is bilateral stimulation in EMDR therapy?

Bilateral stimulation is a rhythmic, side-to-side sensory input used during EMDR therapy. It can take the form of guided eye movements, alternating hand taps on your knees, or audio tones that alternate between your left and right ear. It engages both sides of the brain while you focus briefly on a distressing memory.

How does bilateral stimulation work?

The leading theory is that bilateral stimulation taxes working memory while the brain accesses a distressing memory. This dual attention allows the brain to reprocess the memory so it becomes less emotionally intense. Other theories point to REM sleep-like brain states and disruption of memory reconsolidation.

Is EMDR the same as hypnosis?

No. EMDR is not hypnosis. Clients remain fully awake, aware, and in control throughout every session. You choose what to share and can pause at any time.

Does bilateral stimulation work outside of EMDR?

Bilateral stimulation on its own is not therapy. It is one component of the 8-phase EMDR protocol. Tapping or eye movements alone, without a trained clinician guiding the process, will not produce EMDR's therapeutic effects.

Is EMDR safe for everyone?

EMDR is safe for most adults and children when delivered by a trained clinician. It is often not recommended during pregnancy without modification, and clients with active psychosis or certain dissociative conditions may need extended preparation first. Your therapist will evaluate fit during your first session.

How many sessions of EMDR will I need?

Single-incident trauma often resolves in 3 to 6 sessions. Complex or chronic trauma typically takes 12 to 20 sessions or more. Your therapist will estimate a range after the assessment phase.