EMDR works... but how? Recent progress in the search for treatment mechanisms

Eye movement desensitization and reprocessing (EMDR) is a highly scrutinized but efficacious psychotherapy commonly used in the treatment of posttraumatic stress disorder. Despite much theorizing and speculation, EMDR’s mechanism of action remains unspecified. This article reviews several accounts of how EMDR works to reduce symptoms and/or aid memory reprocessing, including disruption of a traumatic recollection in working memory, increased psychological distance from the trauma, enhanced communication between brain hemispheres, and psychophysiological changes associated with relaxation or evocation of a rapid-eye-movement–like brain state. Several gaps in knowledge are also identified: The working memory account has received considerable support but has yet to be evaluated using clinical samples. How psychological distancing translates into symptomatic improvement is unclear. Psychophysiological effects of EMDR are well demonstrated but leave open the question of whether they constitute a treatment mechanism or an outcome of memory processing. Multiple mechanisms may work to produce treatment gains in EMDR; hence, an integrative model may be necessary to capture its myriad effects.