The Part of EMDR Nobody Can Fully Explain

What bilateral activation is, how it works in practice, and the intuition behind it.

The origin story of EMDR is unusually humble for a therapeutic technique that has since accumulated decades of research and clinical application. In the late 1980s, a psychologist named Francine Shapiro went for a walk. She noticed something about the way her eyes moved as she walked — a natural, rhythmic side-to-side quality — and connected it to a shift in how she was feeling. She wondered if that movement might mean something. She brought the idea into her clinical work, and EMDR was born.

There's something worth sitting with in that story. Not a laboratory discovery. Not a theoretical framework that preceded the practice. A walk. An observation. A question worth trying.

It set the tone for the most mysterious component of EMDR — the part that even its most experienced practitioners can't fully explain.

What bilateral activation actually is

EMDR's full name is Eye Movement Desensitization and Reprocessing, which gives you some sense of where it started. The original technique involved the therapist guiding a client's eyes back and forth — left, right, left, right — while holding a difficult memory or experience in mind. The bilateral movement of the eyes, it turned out, seemed to support the processing of that material in ways that sitting still did not.

Over time, clinicians discovered that eye movement wasn't the only way to achieve this effect. Bilateral audio — alternating tones delivered through headphones, first to one ear then the other — produced similar results. So did tactile activation: small handheld devices that pulse alternately in each hand, or tapping alternately on the knees. The bilateral principle, it seemed, mattered more than the specific method.

In my own practice, I tend to defer to whatever a client finds most comfortable, or whatever is logistically available in a given moment. My working assumption is that any form of bilateral activation has a similar effect on how information gets processed — that the left-right rhythm is what matters, not the particular channel it travels through.

The honest answer about why it works

Here is where I have to be straightforward with you: nobody fully knows.

There are theories. One early explanation pointed to the similarity between bilateral activation and the rapid eye movements of REM sleep — the idea that something about dreaming already does what EMDR does deliberately. It's an appealing connection, but it remains speculative.

What I can offer instead is the closest thing I have to a working intuition about it.

Consider what happens when you go for a walk to work something out. Most people know this experience — the way movement seems to help, the way things that felt stuck begin to loosen. Part of that is probably the change of scene, the rhythm of breathing, the simple act of being in a body in motion. But part of it might also be the bilateral quality of walking itself. Left, right, left, right. Something about that alternating rhythm seems to support the kind of internal processing that sitting still sometimes doesn't.

EMDR may be, in part, a deliberate and concentrated version of something the body already knows how to do.

Vertical and horizontal

I find it useful to think about what EMDR is doing structurally in terms of two directions of connection.

The first is vertical — connecting the layers of experience from top to bottom. Thoughts, emotions, body sensations. Getting them in contact with each other so that experience is held whole rather than in fragments. This is the work of grounding and integration that runs through everything EMDR does.

The second is horizontal — the bilateral activation itself, connecting left to right. Whatever is happening neurologically, the felt experience of bilateral activation is one of the nervous system being engaged across both of its sides simultaneously. Something about that seems to support processing in a way that purely vertical, top-down work doesn't always reach.

Together — top to bottom, left to right — there's something that feels structurally complete about it. I hold that lightly, as a working model rather than an established fact. But it's the frame that makes the most sense to me after years of doing this work.

What it feels like in a session

One thing I can say with more confidence is that bilateral activation creates a container.

When the bilateral activation begins, processing begins. When it stops, processing stops. That boundary — that clear demarcation between being in it and being out of it — is one of the things that makes EMDR feel manageable to people who worry about opening something up without being able to close it again. The bilateral rhythm isn't just a processing tool. It's a frame around the work.

That's not nothing, even if we can't fully explain why it works. Sometimes the most important thing a therapeutic tool can do is make it possible to go somewhere you couldn't go before, and come back.