How EMDR therapy works

I have been researching EMDR, which is a psychotherapy for PTSD. Many advocates and practitioners of EMDR therapy hypothesize that “bilateral stimulation” is an essential component of the therapy’s effectiveness. But recent research on a Working Memory model (“WM”) provide evidence that any sufficiently distracting activity is as effective as directed eye movements or bilateral stimulation. From the best paper I read on this subject:

Traditionally, during EMDR, eyes are moved horizontally. In line with the WM account, but in contrast to original explanations, moving eyes vertically is equally effective. Crucially, the same effects occur if WM is taxed during recall with non-eye-movement secondary tasks, like listening to a series of non-words (auditory shadowing), drawing a complex figure, or counting. Tasks that are presumably hardly taxing, like simple finger tapping, do not have beneficial effects, while more complex tapping does. Likewise, activating memories about a previously seen trauma film while playing taxing computer game reduced flashbacks in the week afterwards. Whereas EMDR has been advocated as treatment for past trauma, the WM theory implies that negative images about future events (‘flashforwards’) can be treated as well. Experimental evidence confirms this. Finally, WM rightly predicts that individuals who are bad at multi-tasking derive more benefit from eye movements, counting, et cetera during recall of negative memories.

EMDR: Eye movements superior to beeps in taxing working memory and reducing vividness of recollections, Behaviour Research and Therapy 49 (2011) 92-98