The "Eye Movement" aspect of EMDR involves me asking you to move your eyes from side to side, following my hand, for short bursts of time, while allowing yourself to recall the bodily feelings, emotions and thoughts associated with a particular traumatic memory. The mechanism by which this works is still being explored in scientific research, but it seems to be concerned with the way in which we store memories. Traumatic events are, by definition, overwhelming: when our safety is at risk we automatically act from the primitive, “action" parts of the brain, without involving the more sophisticated “thinking" parts of the brain. This means that the memory gets stored as an experience to be learnt from in future situations that appear to be similarly threatening. For example, if we once had to escape a burning building, the smell of burning toast might always, even years later, trigger a panic reaction. You could say that we are interpreting the present situation (smoke from toaster) through the physiological effect (panic) of a previously stored experience (house fire).
By targetting the traumatic event and the way it is stored in memory, successful reprocessing with EMDR changes a disturbing memory into one that is no longer emotionally distressing and is now perceived to have taken its appropriate place in the historical past. You are remembering rather than re-experiencing.
We do not have to think of traumatic experiences as being overtly dramatic and life-threatening events. All of us have had experiences that we could call adverse or traumatic, often in childhood. These experiences - just as with more pleasant or positive experiences - contribute to how we shape ourselves, our relationships and our outlook on the world. If an adverse experience leads us to hold a belief that later becomes somewhat limiting, EMDR can help us to go back into our stored memories and do what is called Adaptive Information Processing so that we can come up with a more life-enhancing belief in relation to that particular experience. For example, if when I was six a teacher shouted at me for being selfish, I might, at a deep level, continue to feel ashamed and believe that I am not a nice person, a “truth” that I might have to carefully hide from people. This may sound trivial, but it seems to me that if I were to hold a whole range of negative beliefs about myself - or indeed about the world - then I might well feel very depressed, or perhaps develop obsessive behaviours in an attempt to manage my fears and bad feelings. EMDR reprocessing allows us to re-evaluate the memory that led to a negative self-belief, and to let it be an event that happened but need not shape how we feel about ourselves now.
As I continue to deepen my experience as an EMDR practitioner, I feel very excited about the possibilities that it offers.