Bilateral stimulation in EMDR involves alternating left–right input, such as eye movements, tapping, or sounds. It is used during trauma processing to help the brain integrate distressing memories and reduce their emotional intensity.
The Main Theories Behind Bilateral Stimulation in EMDR
| Theory | Core Idea |
|---|---|
| Working Memory | Divides attention and reduces vividness |
| Orienting Response | Investigate then settle |
| Dual Attention | Maintain awareness of past and present |
| REM Sleep Theory | Memory integration processes |
| Interhemispheric Theory | Increased communication between hemispheres |
What is bilateral stimulation in EMDR?
In EMDR therapy, bilateral stimulation refers to the use of alternating left–right sensory input. Bilateral stimulation refers to the use of alternating left–right sensory input, such as eye movements, tapping, or sounds. It is used during trauma processing to support the brain’s ability to integrate distressing memories and reduce their emotional intensity. Although the exact mechanisms are still being studied, several theories explain how it contributes to therapeutic change.
- A core element of EMDR therapy
- Uses alternating left–right stimulation
- Applied during trauma reprocessing
- Supports adaptive information processing
The clinical effectiveness of Eye Movement Desensitisation and Reprocessing (EMDR) is well established. EMDR is a psychotherapy with a substantial evidence base for post-traumatic stress disorder (PTSD), supported by multiple randomized controlled trials and meta-analyses (Chen et al., 2014; Cusack et al., 2016; Cuijpers et al., 2020). There is also a growing, though less established, evidence base for its application in other conditions, including anxiety disorders, obsessive–compulsive disorder (OCD), and chronic pain (Valiente-Gómez et al., 2017; Yunitri et al., 2020).
During trauma reprocessing, BLS is applied while the client holds a distressing memory, image, or associated somatic experience in mind. Although the effectiveness of EMDR is well supported, Researchers continue to investigate how bilateral stimulation contributes to therapeutic change in EMDR. Several theories have been proposed, and this article is an introduction to some of the most long-standing explanations.
Bilateral stimulation is most commonly associated with trauma memory processing. Slower forms of bilateral stimulation are used to support grounding, dual awareness and nervous system regulation outside formal reprocessing protocols. If it is helpful you can read more about this here.
The Adaptive Information Processing (AIP) Model in EMDR
The Adaptive Information Processing (AIP) model provides the theoretical framework underpinning EMDR therapy. The model proposes that traumatic experiences may become stored in memory networks in a maladaptive form, retaining the original emotions, beliefs, and somatic sensations associated with the event.
When these memories are triggered, individuals may re-experience elements of the original distress. In this way, the individual may experience aspects of the past event as though they are occurring in the present, contributing to symptoms such as intrusive memories, heightened emotional responses, and negative beliefs about the self.
EMDR therapy activates these memories while incorporating bilateral stimulation and structured therapeutic procedures, facilitating the reprocessing and integration of the memory into more adaptive memory networks. As processing occurs, the memory can be retained without the same emotional intensity or dysfunctional beliefs (Shapiro, 2018).
While the AIP model offers a clinically useful explanatory framework, it was originally proposed before much of the current neurobiological research on memory processing. As a result, the precise neural mechanisms involved remain an area of ongoing investigation.
Working Memory Theory: How Bilateral Stimulation Reduces Emotional Intensity
One of the most widely discussed explanations for the effects of bilateral stimulation is working memory theory. Working memory has limited capacity. Recalling a distressing memory while simultaneously performing another task, such as bilateral eye movements, places competing demands on this cognitive system.
This dual task is thought to reduce the vividness and emotional intensity of the memory because performing two tasks simultaneously limits the cognitive resources available to maintain the distressing memory in its original vivid form (van den Hout & Engelhard, 2012; Gunter & Bodner, 2008).
Laboratory studies consistently demonstrate reductions in memory vividness and emotionality when dual-attention tasks are used.
Working memory theory explains part of the process, but it does not fully account for the broader clinical changes observed in EMDR.
While much of the research has focused on relatively rapid bilateral stimulation, slower forms of bilateral auditory stimulation may also play a role in stabilisation and regulation. You can read more about this here: slow bilateral auditory stimulation for stabilisation.
Interhemispheric Communication Theory in Bilateral Stimulation
Early explanations suggested that horizontal eye movements might increase communication between the brain’s left and right hemispheres, facilitating emotional processing of traumatic memories (Propper & Christman, 2008).
However, findings that vertical eye movements and other forms of bilateral stimulation produce similar effects challenge explanations based solely on interhemispheric interaction. As a result, this theory is now considered a partial explanation rather than a comprehensive account of EMDR’s mechanisms.
Why the Mechanisms of EMDR Are Still Being Researched
Despite decades of research, there is currently no single theory that fully explains why bilateral stimulation contributes to therapeutic change in EMDR. Proposed mechanisms include working memory taxation, interhemispheric communication, orienting responses, and broader neurobiological processes related to memory reconsolidation. It is likely that bilateral stimulation engages several interacting cognitive and neurobiological processes rather than a single mechanism.
EMDR has a substantial evidence base as a treatment for trauma. While the precise mechanisms underlying bilateral stimulation continue to be debated, current theories suggest that multiple interacting processes contribute to its therapeutic effects. Bilateral stimulation should therefore be understood not as a standalone intervention, but as one component within a structured therapeutic approach delivered by appropriately trained clinicians.
Clinical Implications: What This Means for Practice
- There is currently no single mechanism that fully explains how EMDR produces therapeutic change. Multiple interacting systems are likely involved.
- Bilateral stimulation should be understood as one component within a structured therapeutic approach, rather than a standalone intervention.
- The evidence base supports the use of relatively rapid bilateral stimulation within the standard EMDR protocol.
- Stabilisation and preparation remain essential prior to trauma processing.
- Slower forms of bilateral stimulation may be used within stabilisation work but are distinct from reprocessing phases and should be applied with clinical judgement.
Key Takeaways
- Several theories attempt to explain how bilateral stimulation may contribute to therapeutic change.
- Working memory theory currently has some of the strongest empirical support.
- No single theory fully explains all observed effects.
- Bilateral stimulation is most commonly associated with EMDR reprocessing, although slower forms are increasingly being explored within stabilisation-focused work.
Audio Resources for Clinical Practice
In practice, many clients struggle most with maintaining regulation between sessions—particularly following difficult or activating work.
To support this phase of therapy, I’ve developed clinician-designed bilateral audio resources for stabilisation and nervous system regulation between sessions.
• Explore the full audio library → Willow Tree Wellbeing Audio Library
• Or try a short stabilisation audio → Access a Free Stabilisation Audio Sample
About the Author
Donna Dickinson is a BABCP-accredited CBT therapist and EMDR-trained psychotherapist with over 19 years of NHS experience in trauma-focused work. Her clinical interests include nervous system regulation and stabilisation in therapy. She develops clinically informed audio resources to support stabilisation and regulation within trauma-informed practice.
References
Chen, L., Zhang, G., Hu, M., & Liang, X. (2014). Efficacy of eye-movement desensitization and reprocessing for patients with posttraumatic stress disorder: A meta-analysis of randomized controlled trials. PLoS ONE, 9(8), e103676. https://doi.org/10.1371/journal.pone.0103676
Cusack, K., Jonas, D. E., Forneris, C. A., et al. (2016). Psychological treatments for adults with posttraumatic stress disorder: A systematic review and meta-analysis. Clinical Psychology Review, 43, 128–141.
Cuijpers, P., Veen, S. C., Sijbrandij, M., et al. (2020). Eye movement desensitization and reprocessing for mental health problems: A systematic review and meta-analysis. Journal of Behavior Therapy and Experimental Psychiatry, 69, 101564.
Gunter, R. W., & Bodner, G. E. (2008). How eye movements affect unpleasant memories: Support for a working-memory account. Behaviour Research and Therapy, 46(8), 913–931.
Lee, C. W., & Cuijpers, P. (2013). A meta-analysis of the contribution of eye movements in processing emotional memories. Journal of Behavior Therapy and Experimental Psychiatry, 44(2), 231–239.
Propper, R. E., & Christman, S. D. (2008). Interhemispheric interaction and saccadic horizontal eye movements. Journal of EMDR Practice and Research, 2(4), 269–281.
Shapiro, F. (2018). Eye Movement Desensitization and Reprocessing (EMDR) Therapy (3rd ed.). Guilford Press.
van den Hout, M. A., & Engelhard, I. M. (2012). How does EMDR work? Journal of Experimental Psychopathology, 3(5), 724–738.
Valiente-Gómez, A., Moreno-Alcázar, A., Treen, D., et al. (2017). EMDR beyond PTSD: A systematic literature review. Frontiers in Psychology, 8, 1668.
Yunitri, N., Chu, H., Kang, X. L., et al. (2020). The effectiveness of EMDR toward anxiety disorder: A meta-analysis of randomized controlled trials. Journal of Psychiatric Research, 123, 102–113.