Working Memory Theory of EMDR

The working-memory theory is one of the most-studied explanations of why bilateral stimulation may help in EMDR. In one sentence: recalling a memory and performing a demanding task at the same time compete for limited working-memory capacity, so the memory is held less vividly and emotionally, and it may be stored again in that less intense form.

The mechanism. Working memory is the limited system that holds and manipulates information over short periods (Baddeley, 2000). Andrade, Kavanagh and Baddeley (1997) showed that eye movements reduced the vividness and emotionality of recalled images, and that other visuospatial tasks had similar effects. Gunter and Bodner (2008) found that eye movements and other demanding tasks reduced the unpleasantness of memories, and that the effect was not limited to horizontal eye movements — consistent with a general working-memory account rather than something unique to bilateral movement.

Load matters. Van den Hout and Engelhard (2012) reviewed experiments showing that tasks which tax working memory more tend to produce larger reductions, and that the effect depends on individual capacity. Studies on eye-movement speed point the same way (Maxfield et al., 2008; van Veen et al., 2015).

Meta-analytic support. Lee and Cuijpers (2013) concluded that eye movements contribute to the effect of processing emotional memories in both laboratory and clinical studies.

What is supported: dual tasks during recall reduce the vividness and emotionality of memories in laboratory studies, and load appears to matter.

What remains theoretical or uncertain: most experiments use non-clinical participants and short-term outcome measures; how fully these effects explain the clinical results of EMDR for PTSD is not settled. Other mechanisms have been proposed, including orienting responses and physiological de-arousal (Landin-Romero et al., 2018). Neuroimaging findings are preliminary and should not be presented as proof of a mechanism.

What it suggests for practice: stimulation should engage the client's attention without overwhelming them, and speed or modality may be adjusted to the individual. Exact settings remain a clinical decision — see BLS speed and set length.

The Adaptive Information Processing (AIP) model is the clinical framework that guides the eight-phase protocol. The working-memory theory is a narrower, testable account of what happens during sets of bilateral stimulation. They are generally seen as complementary rather than competing. More in the AIP model.

If load matters, modalities that tax working memory more might be expected to have larger effects. In one laboratory study, alternating tones taxed working memory less than eye movements and produced smaller effects (van den Hout et al., 2012). See visual vs. auditory vs. tactile BLS and the bilateral stimulation overview.