What Is the Interference Stimulus?

EMDR (Eye Movement Desensitization and Reprocessing) has transformed the way clinicians approach trauma. But what exactly makes it so effective? Is it the bilateral stimulation? The eight-phase protocol? Or is there something deeper at play in the brain?

In this blog post, we unpack one of the leading theories behind EMDR’s effectiveness: working memory taxation. Drawing from neuroscience, clinical research, and therapist experience, we explore how EMDR works by engaging specific brain systems and redistributing attention and memory resources. This post is ideal for clinicians, students, and curious learners who want to understand the science behind EMDR in clear, accessible terms.

What is Working Memory, and Why Does It Matter in Trauma Therapy?

Working memory is your brain's ability to hold and manipulate information over short periods of time. It’s the mental workspace where you solve problems, remember a phone number long enough to dial it, or pay attention while taking notes.

In the context of trauma, working memory becomes critical because:

• Traumatic memories often dominate attention.
• When the brain is flooded with fear or shame, it struggles to stay in the present.
• Engaging working memory during trauma recall may disrupt the brain’s typical response pattern.

This is the heart of working memory theory in EMDR: if a client holds a traumatic image in mind while simultaneously completing a working memory task (like tracking a moving object), the emotional vividness of the memory is reduced.

"It’s not just distraction—it’s reconsolidation. You’re using one part of the brain to loosen the grip of another."

Research supports this. Studies by Van den Hout, Engelhard, and others (2012) show that taxing working memory reduces the emotional intensity and vividness of traumatic memories.

Understanding the Brain: From Modules to Networks

Early neuroscience often focused on modular thinking:

• Fear = amygdala
• Memory = hippocampus
• Attention = prefrontal cortex

While useful, this model doesn’t explain why trauma affects everything at once.

Enter network neuroscience, a more recent and comprehensive model. Instead of isolated parts, brain functions are distributed across large-scale systems called intrinsic connectivity networks. These networks regulate everything from thought and memory to emotion and attention.

Among the most important are:

1. Default Mode Network (DMN) – self-reflection, autobiographical memory
2. Salience Network (SN) – threat detection, switching between networks
3. Central Executive Network (CEN) – working memory, decision-making

When trauma occurs, these networks lose synchrony. Clients may:

• Loop in shame (DMN)
• Feel hypervigilant or numb (SN)
• Struggle to think clearly (CEN)

What EMDR Is Doing in the Brain

During EMDR, when a distressing memory is activated:

• The Salience Network (SN) flags it as important.
• The Default Mode Network (DMN) brings up self-referential associations.
• The Central Executive Network (CEN) tries to stay present.

Dual attention tasks, such as bilateral stimulation, tax the CEN, anchoring the client in the present moment. This reduces the cognitive resources available to the DMN, weakening the emotional grip of the memory. Meanwhile, the SN helps orchestrate the shift between past and present.

"The SN becomes the conductor, coordinating two orchestras: past (DMN) and present (CEN)."

Memory Reconsolidation in EMDR

Neuroscience shows that memories are not fixed. According to Nader et al. (2000), a memory becomes labile (changeable) when it is reactivated. If, during that reactivation, new information is introduced, the memory can be reconsolidated in a less distressing form.

EMDR leverages this by:

• Activating the memory (DMN)
• Providing a new experience (CEN + therapeutic presence)
• Re-tagging the emotional salience (SN)

It’s not that the memory disappears. It’s that the brain knows how to relate to it differently.

Critiquing Working Memory Theory: What It Gets Right and What It Misses

What It Gets Right:

• Working memory tasks disrupt trauma memory vividness.
• Bilateral stimulation engages attention and reduces fear.
• Dual-task interference is measurable and repeatable in lab settings.

What It Misses:

• EMDR is not a mechanical task. Relationship matters.
• Trauma isn’t just about intensity—it’s about meaning.
• The SN requires emotional safety to flag experiences as worth integrating.

"The working memory load softens the emotional punch, but it’s the network reconnection—guided by safety and co-regulation—that allows transformation."

Clinical Takeaways: How to Use This Understanding in Practice

• When you slow down and attune to your client, you’re helping their Salience Network reclassify experience from threat to meaning.
• When you invite parts to speak, you’re engaging DMN + SN.
• When you use BLS while grounding, you’re co-activating CEN + SN.

By working relationally with the client, you’re helping the brain do what it was always meant to do: integrate.

Want More?

• Episode 2 of the series explores large-scale brain systems and how EMDR creates reconnection across networks.
• Upcoming episodes dive into AI-supported EMDR and EMDR 2.0 with Dr. Suzy Matthijssen.

Further Reading:

• Van den Hout, M., & Engelhard, I. (2012). How does EMDR work? Journal of Experimental Psychopathology.
• Nader, K., Schafe, G. E., & LeDoux, J. E. (2000). Fear memories require protein synthesis in the amygdala for reconsolidation after retrieval. Nature.
• Chamberlin, E. (2022). The Neurophysiology of EMDR and the Three Core Networks.
• Siegel, D. J. (2012). The Developing Mind: How Relationships and the Brain Interact to Shape Who We Are.

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