Background: Controversy continues to exist regarding how EMDR works and whether its mechanisms differ from those at work in standard exposure techniques.
Aims: To investigate first whether eye movement bilateral stimulation is an essential component of EMDR and, second, the current status of its theoretical basis.
Method: A systematic search for relevant articles was conducted in databases using standard methodology.
Results: Clinical research evidence is contradictory as to how essential EMs are in PTSD treatment. More positive support is provided by analogue studies. With regards to potential theoretical support, some evidence was found suggesting bilateral stimulation first increases access to episodic memories; and second that it could act on components of working memory which makes focusing on the traumatic memories less unpleasant and thereby improves access to these memories.
Conclusions: The results suggest support for the contention that EMs are essential to this therapy and that a theoretical rationale exists for their use. Choice of EMDR over trauma-focused CBT should therefore remain a matter of patient choice and clinician expertise; it is suggested, however, that EMs may be more effective at reducing distress, and thereby allow other components of treatment to take place.