Eye Movement Desensitization and Reprocessing (EMDR)
EMDR Certified Therapist
Member EMDR Canada
Affiliate Member EMDR International Association
What is EMDR and how does it work?
EMDR is an evidence-based therapy that stands for Eye Movement Desensitization and Reprocessing.  EMDR processes material that has been maladaptively stored in the brain and has not been processed adequately, which keeps the person stuck and symptomatic. 
One metaphor that can be helpful in conceptualizing how EMDR works is by thinking about a filing system. The traumatic memories, including sights, sounds, feelings, thoughts, and body sensations are not properly filed in the brain, which allows them to be easily triggered at any moment, often unexpectedly. EMDR takes intrusive memories and puts them in proper files, removing the vividness and the distressing emotional qualities.
What problems does EMDR treat?
EMDR can significantly reduce the symptoms associated with PTSD triggered by war, overseas peace-keeping, first-responder trauma, car accidents, or medical procedures. 
EMDR is also effective for past or current relational trauma. Relational trauma may include past childhood abuse and neglect, witnessing parental violence, childhood bullying, 
sexual harassment or assault, domestic violence in romantic relationships, being fired from work, abuse in the workplace, grief and loss, and other adverse life events. Anxiety, phobias, depression and other mental health concerns can treated successfully using EMDR.
Mechanisms of EMDR
Through brain imaging research, we know that the amygdala becomes hyper-activated in people who have PTSD, making them vulnerable to fight/flight/freeze reactions even when there is no longer an actual threat. Research also shows that (a) goal-directed eye movements alone can deactivate the amygdala and (b) taxing the working memory with distractor tasks can deactivate the amygdala (e.g., holding the memory in mind while visually tracking the therapist's  hand movements).
Activate the Traumatic Memory + Desensitize by taxing the working memory
During an EMDR session, one memory will be selected from a list of traumatic memories already developed by the client and therapist in session.  The therapist then asks the client to describe an image that represents the worst part of the memory, provide a negative cognition (e.g., I am powerless or I am unworthy), identify the emotions and body sensations that goes with it, and determine the Subjective Unit of Disturbance rating on a scale of 0 to 10.
Once the memory is fully activated and held in the client's working memory, the therapist engages the client in one or more distractor tasks to desensitize the memory. Typically the distractor task is very fast eye movements, but a growing body of research finds that additional distractor tasks (e.g. concurrent auditory or tactile stimulation, complex rhythms with or without music, spelling or math problems, surprise hand movements such as a clap,) can and should be used to maximally tax the working memory. During the desensitization, the vividness and emotionality of the memory decreases to the point that it is no longer disturbing.
Why does the traumatic memory change?
Research on memory reconsolidation provides evidence that activating a memory with strong emotion (e.g., a traumatic and fearful incident) under certain conditions can temporarily disrupt or destabilize the memory (e.g., open it up). When a prediction error is introduced with mismatched or contradictory information (e.g., doing distracting tasks or realizing that "I am safe now"), the new information has the potential to change and erase the old memory and its disturbing reactivity.