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Eye movement desensitization and reprocessing, or, as it is more commonly known, EMDR, is a much-hyped and highly successful psychotherapy technique used to treat anxiety as well as post-traumatic stress disorder and addiction. The subjects have to recall the traumatic or anxiety-producing event while performing various directed eye movement exercises. EMDR has been spreading quickly in psychiatric practices all over the world, given its success rate.
The problem is that it is not at all obvious why EMDR works, let alone why it works as well as it does. Why would moving your eyes help you with your traumas? Given the questions about the exact mechanism of EMDR, there are some voices calling it a pseudo-scientific fad. I want to argue that there is a straightforward and very clear explanation for why EMDR works, but for that we need to put together three very different sets of empirical findings about the mind:
- A. We know from a number of studies that mental imagery is a central ingredient of episodic memory. The loss of the capacity to form mental imagery results in the loss (or loss of scope) of episodic memory. An even more important set of findings is that relevant sensory cortical areas are reactivated when we recall an experience.
- B. We also know that episodic memory is constructive: Remembering an event we have experienced is not the mere accessing of the memory trace, but the active construction of a memory. So recalling a memory is not like taking it out of a box and then, when you're done with it, putting it back where you found it. The very act of remembering changes the memory trace. In short, remembering an event changes the way it is encoded, so next time you will remember it differently.
- C. Finally, we have also have a lot of evidence for the role of eye movements in mental imagery. Our eye movement during visual imagery re-enacts that of the perception of the same visual scene. When we visualize a scene, our spontaneous eye movements reflect the content of the visual scene. For example, when we perceive a pattern in a grid, our eye movements are isomorphic to our eye movements when we visualize the same pattern. Further, artificially blocking eye movements impairs the vividness (and often even the feasibility) of mental imagery formation.
If we put these three pieces together, it explains why EMDR works the way it does. When the subject recalls the traumatic event while moving their eyes, this reduces the vividness of the mental imagery involved in that episodic memory, given that incongruous eye movement reduces the vividness of mental imagery. And because the very act of remembering an event changes its representation in memory, when this memory gets re-encoded, it will be encoded in a less vivid manner.
So EMDR is not a pseudo-scientific fad. There are clear reasons why it works, but these come from different corners of psychological research. And understanding these reasons can help us to improve this already effective way of treating a wide range of trauma-related problems.
