EMDR is an information processing therapy and uses an eight phase approach to address the experiential contributors of a wide range of pathologies. It attends to the past experiences that have set the groundwork for pathology, the current situations that trigger dysfunctional emotions, beliefs and sensations, and the positive experience needed to enhance future adaptive behaviors and mental health.
Basically, EMDR is a therapeutic technique in which the patient moves his or her eyes back and forth while concentrating on a problem or a traumatic memory. The therapist waves a stick or light in front of the patient and the patient is supposed to follow the moving stick or light with his or her eyes. The therapy was discovered by therapist Dr. Francine Shapiro while on a walk in the park.
Noone is really 100% sure of how EMDR actually works. A commonly proposed hypothesis is that dual attention stimulation elicits an orienting response. The orienting response is a natural response of interest and attention that is elicited when attention is drawn to a new stimulus.
Another theory is that humans naturally process memories and new informaion during REM sleep, but with traumatic memories this processing does not fully occur, leaving the memories unstored and still strongly connected to emotions and physical sensations. The idea here is that the eye movment in EMDR simulate REM sleep allowing the memory which is beng focused on to process.
However, there is a lot of empirical evidence for the effectiveness of EMDR, esspecially in the treatment of PTSD.