The human brain processes and stores information about experience. It forges links between information currently being processed into memory and other relevant thoughts, ideas, and memories. Shapiro hypothesizes that during a traumatic event normal information processing may be disrupted. This may be due to the strong emotions being felt, or due to dissociation. As a result, information about the event is not fully processed into an adaptive network with other ideas, thoughts, and memories (1). An example of a maladaptive association is a rape survivor knowing that the rapist is the one to blame, and yet acutely feeling as if the rape were their own fault. Shapiro points to these mal-processed experiences as the seat of dysfunction and mental disorder, such as Post Traumatic Stress Disorder (PTSD) and Acute Stress Disorder (ASD), the two main mental disorders that Eye Movement Desensitization and Reprocessing (EMDR) is used to treat (1). The role of EMDR in Shapiro’s hypothesis is to resume and complete the processing of relevant information into adaptive networks. When the incident is recalled, post-therapy, according to Shapiro, the individual should have a new perspective and insight, and is no longer overcome with the excessive emotion and vividness of the incident that plague sufferers of PTSD and ASD.
EMDR therapy occurs in eight stages including assessing the patients readiness for the procedure, the procedure itself, closure, and evaluation of the success of the procedure. The procedure itself also occurs in repeated steps. The patient calls to mind a vivid visual image, negative thought, or bodily stimulus associated with the negative event while following the therapist’s finger as it moves back and forth for approximately 30 seconds (1). These eye movements can be replaced with auditory tones alternating between the left and right ear, or bilateral tactile stimulation of the left and right knees. This is called dual attention stimulus. This step is repeated numerous times until the patient does not report distress at the chosen negative association. The patient then chooses a positive image, thought, or sensation that they would like to replace the negative one and repeats the procedure (1). They follow the therapist’s finger back and forth for 30 seconds until they report that the positive association feels more valid than the negative one. This combination of recall and dual attention stimulus is the key to EMDR.
A number of studies have been done comparing EMDR to no therapy, cognitive behavioral therapy, non-exposure therapy and exposure therapy (without eye movements). EMDR has been shown to be more effective than no treatment and non-exposure treatments, but no more effective than other exposure treatments. This meta-analysis of 34 studies was done by Davidson and Parker (2). Even though EMDR may be no more effective than exposure therapies it still may be preferable. Exposure therapies involve putting the patient in a situation where they must confront the traumatic event or trigger with the therapist while they work through the initial fear to accept that the memory or thing is not truly threatening. This process, though effective, forces the patient to experience anxiety provoking stimuli which may be very distressing. Logistically the process also may be difficult to arrange. EMDR is (typically) not at all distressing, and is a very simple procedure to perform. Multiple other studies have had conflicting results, sometimes showing EMDR to be no more effective than alternative or no therapy.
Even with these inconsistent research results EMDR is still a novel treatment receiving attention by therapists and researchers, and is being used more frequently in PTSD and ASD patients. In 2004 it was approved by the American Psychiatric Association for treatment of PTSD (1). Perhaps the most interesting aspect of EMDR, and the reason it is being given attention, is its utilization of dual attention stimuli in a process that targets memory and emotion. There is something novel and intriguing about a psychological therapy that claims to benefit from the co-occurrence of a seemingly random and unrelated physical stimulus.
It is obvious that our bodies and minds are highly intertwined, that there is a strong psycho-physiological relationship. If EMDR with dual attention stimuli is more effective than without it there is a significant connection between information processing and eye movements (or any bilateral alternating stimulus). We smile when we are happy, we fall asleep when we lie down in bed, we walk to the refrigerator when we are hungry. The direction of interaction is hard to tease out, do we get into bed when we are tired or are we tired because we have gotten into bed? It could be either. These mentioned physical movements are an expression of, or action related to, a specific internal state such as fatigue. These relationships are clearer than the one that exists between dual attention stimuli and memory.
What possible role could eye movement have in the mechanism of information processing? When PTSD sufferers recall their traumatic memories there is increased activity in areas of the right hemisphere responsible for visual images and emotional activity, and decreased activity as compared to normal in Broca’s area (located in the left hemisphere), which is responsible for speech (6). This may explain why PTSD sufferers talk about their trauma in implicit perceptual terms, as opposed to a reflective story telling manner (6). The increase in norepinephrine, which is involved with the hippocampus in long term memory storage, experienced during stressful events may be responsible for the perpetual lifelike vividness of traumatic memories. The alternating bilateral nature of a dual attention stimulus may activate the left and right hemispheres alternatively. This may assist in the integration of the previously right hemisphere isolated traumatic memory into a bilateral network of associations with past memories and current thoughts related to the event (4). This may allow for a reflective interpretation of the event, now mediated by experience. Even if the stimuli does activate the hemispheres alternatively, it is unclear precisely what areas of the hemispheres are being activated and what specific role they play in processing memories. If the eye movements do have a neurobiological function in this treatment, is bilateral hemisphere activation the mechanism of its function or is there something else occurring?
There are three main hypotheses for the mechanism of action of the dual attention stimuli in EMDR. Kavanaugh posits that the dual attention stimulus serves to interrupt and disrupt the negative associations formed by the traumatic memory. When the existing associations are disrupted new associations can form (1). Because the new associations are formed in the context of therapy they are more adaptive than those formed during the traumatic event. The following two hypotheses are especially intriguing, due to their evolutionary and neurobiological foundations, if not terribly more scientifically provable than the first.
The second hypothesis is posited by MacCulloch, Feldman Barrowcliff, and Van Den Hout. It states that the eye movements are part of an investigatory response, which is part of orienting behavior (4). They seem to propose that when a danger is encountered the first response is fear and a negative physical response and the second step is investigatory behavior, looking for further danger, which can lead to avoidance or approach. Investigatory behavior can result in a positive physical response, relaxation, when it is assessed that there is no further threat (4). If this is the case then the relaxation should occur during EMDR only in trials where the patient is thinking about the traumatic memory. On the trials where the patient is targeting a positive memory no orienting response to danger, and therefore no investigatory response followed by relaxation should occur. Indeed this is supported in a study by a study done by Barrowcliff et al (5).
The third hypothesis is being investigated by Stickgold, Christman, and Garvey. They take a hard neurobiological approach to the problem. They believe that the dual attention stimuli trigger a neurobiological state which is conducive to the conversion of episodic memory to cortical semantic memory. They believe that the eye movements used in therapy mimic the saccades of rapid eye movement (REM) sleep, inducing a similar neurobiological state (4). Many researchers believe that REM sleep is a critical time for integration of stored episodic memory into long term semantic networks. They suggest that the integration of the hippocampally stored target memory into a general semantic network serves to lessen the strength of the memory and its associated amygdally located fear response.
There is still much contention as to the relative efficacy and mechanism of action of eye movement desensitization and reprocessing therapy. Further research with more strictly controlled conditions may elucidate the effects of EMDR as compared to alternative therapies, and serve to further validate its acceptance into common practice. EMDR is still in many ways a mystery. In our attempts to figure out exactly what is occurring inside this black box we are, and can learn a lot about the mechanism of information processing and memory storage, how these processes work, and how they are affected by external variables, such as trauma. Through studying its parallels with other biological processes such as sleep we can learn more about the mechanisms of both, as well as about common patterns underlying varied biological functions.