How Does EMDR Work? The Science Behind the Therapy
Find out what makes EMDR work...
EMDR has a reputation for sounding unusual. The description — a therapist moving their fingers side to side while a client recalls a traumatic memory — doesn’t map onto most people’s understanding of how therapy works. It sounds more like something from an alternative wellness catalogue than from the evidence base of modern psychology.
Which makes it worth explaining properly. Because EMDR is one of the most rigorously researched trauma treatments available, recommended by the World Health Organization, the American Psychological Association, and numerous national health bodies worldwide. The mechanism isn’t mysterious once it’s understood. And for people who have been carrying unprocessed trauma that hasn’t responded to talk therapy alone, understanding how EMDR works is often the first step toward realizing it might be worth trying.
The Problem EMDR Is Solving
To understand how EMDR works, it helps to start with what it’s addressing — which is not simply the presence of a bad memory, but a specific problem with how that memory is stored.
Under ordinary circumstances, the brain processes experiences in a way that integrates them into long-term memory with appropriate emotional context. Something difficult happens. The nervous system activates. The experience is encoded, processed, and filed — accessible when needed, but no longer carrying the immediate emotional charge of the original event. We can recall a past difficulty without reliving it. The memory is there; the crisis is past.
Traumatic experiences often don’t get processed this way. The overwhelming nature of the event — the intensity, the threat, the helplessness — can disrupt the normal processing cycle, leaving the memory stored in a fragmented, unintegrated form. Rather than being filed as a completed past event, it remains in a raw state in the nervous system — vivid, close to the surface, and capable of being reactivated as though the threat were present rather than historical.
Tamari Thompson-Kraft, Registered Psychotherapist and EMDR specialist at Reset Counselling & Psychotherapy, has spent over fifteen years working with trauma clients and describes this storage problem in terms that immediately resonate with people who live with its consequences: “Your brain is like a big filing cabinet, constantly organizing thoughts and experiences into sections. What happens with trauma is that the thought gets stuck — our brain doesn’t know where to put it. As a result, we end up having recurring thoughts, dreams, flashbacks because our brain doesn’t have a category for it.”
That stuck file is precisely what EMDR addresses. Not by talking about the memory until it becomes manageable, but by activating the brain’s own processing system in a way that allows the memory to finally be filed — to become information about something that happened rather than an ongoing experience of something that is happening.
The Role of Bilateral Stimulation
The element of EMDR that most distinguishes it from other approaches — and that most often produces the “that sounds strange” response — is bilateral stimulation. In a standard EMDR session, while holding the traumatic memory in mind, the client follows the therapist’s fingers moving side to side, or taps alternating knees, or listens to tones alternating between left and right ears. This side-to-side, left-right, alternating stimulation is the bilateral component.
Why does this matter? The honest answer is that researchers are still refining the exact neurological explanation, but several mechanisms have strong support.
The most influential theory draws on the parallel between bilateral stimulation in EMDR and what happens during REM sleep. REM sleep — the stage of sleep characterized by rapid eye movements — is the stage during which the brain processes and consolidates emotional memories, integrating the day’s experiences and reducing their emotional charge. The eye movements of REM sleep are bilateral. The hypothesis is that the bilateral stimulation of EMDR activates a similar processing mechanism — essentially triggering, in a waking and controlled state, something neurologically similar to what the sleeping brain does with difficult experiences.
This theory is supported by neuroimaging research showing that EMDR produces changes in brain activation patterns consistent with improved memory consolidation and reduced amygdala reactivity — the amygdala being the brain region most centrally involved in the threat response that traumatic memories activate.
A second mechanism involves what’s called the orienting response — the brain’s automatic shift of attention toward something new and salient in the environment. Bilateral stimulation may occupy enough of the brain’s processing capacity to prevent the full emotional flooding that typically accompanies direct engagement with traumatic material, allowing the memory to be accessed with reduced activation and therefore processed more effectively.
A third mechanism involves dual attention — the requirement to hold two things in mind simultaneously, the traumatic memory and the bilateral stimulation. This dual focus appears to prevent the complete immersion in the traumatic memory that would otherwise occur, maintaining the person in what therapists call the dual awareness state: one foot in the present, one foot in the past, present enough to process without being overwhelmed.
The Eight Phases of EMDR
EMDR is a structured protocol that unfolds across eight phases, and understanding the structure helps clarify why the approach takes the form it does.
Phase 1: History-taking. The therapist builds a thorough understanding of the client’s history, presenting concerns, and therapeutic goals. Importantly, they identify not only the target memories for processing but also the resources and stability the client has available — because processing traumatic material requires sufficient internal stability to do so safely.
Phase 2: Preparation. Before any processing begins, the therapist builds the foundation for it. This includes psychoeducation about trauma and the EMDR process, development of stabilization and distress tolerance skills, and the establishment of what’s called a safe place — a mental image of safety and calm that can be returned to if processing becomes too intense. For people with complex trauma, this phase can take multiple sessions. It isn’t preliminary to the real work. It is the real work, for a period.
Phase 3: Assessment. The specific target memory is identified and its components mapped out — the image that best represents the memory, the negative belief about the self that accompanies it (such as “I am not safe” or “I am worthless”), a preferred positive belief, the emotions associated with the memory, and the physical sensations it produces. This mapping creates the foundation for the processing that follows.
Phase 4: Desensitization. This is the phase most associated with EMDR in popular understanding. The client holds the target memory in mind while engaging in sets of bilateral stimulation, pausing after each set to report what comes up — images, thoughts, emotions, sensations, memories. The therapist guides the process, following what emerges rather than directing it toward a particular outcome. The distress associated with the memory is measured at intervals using the Subjective Units of Distress scale (SUDS), and the phase continues until the distress reduces to a minimal level.
Phase 5: Installation. Once the distress associated with the target memory has reduced, the positive belief identified in Phase 3 is installed — strengthened through bilateral stimulation until it feels fully true in relation to the original memory. The Validity of Cognition scale (VOC) measures the degree to which the positive belief is felt as genuinely true rather than intellectually accepted.
Phase 6: Body scan. The client holds the target memory and the positive belief in mind together while scanning the body for any residual tension, discomfort, or disturbance. If anything is found, it’s addressed with further bilateral stimulation. The body scan reflects EMDR’s recognition that trauma is stored in the body as well as in memory and narrative.
Phase 7: Closure. Every session is closed in a way that returns the client to a state of equilibrium — regardless of whether processing is complete. This might involve the safe place visualization from Phase 2, grounding techniques, or other stabilization strategies. The client is briefed on what to expect between sessions, including the possibility of continued processing, vivid dreams, or unexpected emotional material arising.
Phase 8: Reevaluation. At the beginning of subsequent sessions, the therapist checks whether the processing from the previous session has held, whether new material has emerged, and whether the work can proceed to the next target.
What the Processing Actually Does
What changes through EMDR processing is worth understanding specifically, because it differs from what most people expect.
EMDR doesn’t erase memories. The events that are processed are still accessible afterward. What changes is how they’re stored and how they’re experienced. A memory that was raw, intrusive, and activating — that arrived with the physiological charge of an ongoing threat — typically becomes something that can be recalled without that charge. Still real. Still part of the person’s history. But no longer experienced as present danger.
The negative beliefs associated with the traumatic memory tend to shift as well. The “I am not safe,” “I am worthless,” “It was my fault” that the nervous system has been organizing around are updated through the processing — not through cognitive challenge or argument, but through the integration of the memory itself, which naturally produces a different assessment of what happened and what it means about the person who experienced it.
And the physical symptoms — the hypervigilance, the startle response, the chronic activation, the intrusive sensations — typically reduce as the memories driving them are processed. This is the mind-body connection that Tamari identifies as central to EMDR’s effectiveness: “EMDR can really help because it’s such a mind-body connected therapy.” The processing doesn’t only change the cognitive relationship to the traumatic memory. It changes the nervous system’s response to it.
Who EMDR Is For
EMDR has the strongest evidence base for PTSD following discrete traumatic events — accidents, assaults, medical emergencies, natural disasters. For this presentation it produces results that are often faster than other approaches and highly durable.
It’s also used effectively for complex trauma — the accumulated impact of chronic, relational, or developmental trauma — though the protocol requires more preparation time and moves more gradually through a more complex network of connected memories and beliefs.
Beyond trauma, EMDR has growing evidence for anxiety disorders, depression with traumatic roots, grief, phobias, and the specific presentations where a distressing experience is maintaining current symptoms even when the original event isn’t obviously connected to what the person presents with. Tamari’s observation — “You might be coming in with one concern, but EMDR is good at tackling underlying issues that might be holding you back” — reflects what clinicians with significant EMDR experience consistently find: the presenting concern often has roots that EMDR reaches in ways that surface-level approaches don’t.
EMDR Therapy in Barrie
At Reset Counselling & Psychotherapy, Tamari Thompson-Kraft is a registered psychotherapist with over fifteen years of experience working with trauma clients and specialized training in EMDR. She works with the full range of trauma presentations — single-incident PTSD, complex trauma, childhood experiences, grief, and the quieter ways that unprocessed experiences show up in daily life — offering both individual trauma therapy and EMDR as a primary modality.
We offer trauma and PTSD counselling in person at our Barrie location and virtually across Ontario. No referral needed.
Reset Counselling & Psychotherapy is located at Unit 201-151 Essa Road, Barrie, ON. We offer EMDR therapy, trauma counselling, PTSD treatment, and a full range of mental health services, in person and virtually across Ontario.