Two years ago, I wrote an opinion/commentary questioning the scientific validity of Eye Movement Desensitisation and Reprocessing (EMDR) as a psychotherapeutic intervention. It was based on a systematic review and meta-analytic study by Cuijpers and colleagues that was published in 2020. I had concluded then that exposure probably played a critical role as the main mechanism of action in EMDR. I had also noted that while bilateral stimulation did not appear to directly influence the treatment outcome, it could potentially influence the process by making the exposure more bearable. To quote my article then:
“Also, while the eye movement/bilateral stimulation in EMDR may not affect treatment outcomes, it might make the treatment process more tolerable. As much as exposure is the active ingredient in trauma and anxiety treatments, the process of exposure is difficult. Studies have found the attrition (dropping out of treatment) rates in exposure therapy for PTSD to range between 24-33%! That is to say, a quarter to a third of therapy clients drop out of their treatment for PTSD. If bilateral stimulation, which may reduce the emotional intensity of the exposure process through attentional shifting/dual task interference, could reduce attrition rates, perhaps EMDR might take the win in that regard.
As a counter point however, perhaps attentional shifting/task interference could also be achieved through the use of other strategies unrelated to EMDR, such as progressive muscle relaxation (PMR)/relaxation strategies during exposure. In my own clinical practice, some of my clients have made tremendous progress through exposure therapy when a technique like PMR was first introduced at the start of the exposure treatment, and subsequently faded off after they have built their confidence in confronting their feared stimuli.”
Since my previous article, new research has been published which lends credibility to this line of inquiry. In today’s article, I will be revisiting the topic of EMDR by reviewing a study published in November 2022 on the possible mechanism of action in EMDR.
Study premise
Wadji and colleagues were keen to evaluate if the observed effects of EMDR could be better explained by dual taxation on the working memory. Dual taxation essentially is the process of multi-tasking, which places a higher cognitive load on a person’s working memory as existing resources is split between two simultaneous tasks.
“Dual taxation takes place when an individual recalls a distressing memory while also performing a bilateral stimulation or secondary task, such as EM, mental arithmetic, or drawing complex figure. During the session, the therapist works on memory retrieval while getting the patient to engage in a secondary task. It can be suggested that the secondary task distracts attention away from the retrieval of memory.“
– Wadji, Martin-Soelch, & Camos (2022).
In order to evaluate their hypothesis, Wadji et al. trawled the literature for relevant articles. Using the PRISMA framework, they had identified 11 independent studies published between 2011 to 2021 which met their research criteria.
- Five studies included participants who had post-traumatic stress symptoms, while the other 6 included participants who did not have post-traumatic stress disorder (PTSD) or other mental health conditions, but who were exposed to traumatic stimuli.
- Ten of the 11 studies engaged in EMDR recall with eye movements, while 5 of the 11 studies engaged in exposure with other distractor tasks (e.g. counting, playing Tetris).
- Four studies directly compared EMDR (recall with eye movements) with exposure with secondary distractor tasks.
Findings
Based on the systematic review, the following were found:
- There was a reduction in the intensity (vividness and emotionality) of active recall (e.g. imaginal exposure) across dual taxation conditions (i.e. eye movement or another distractor task) in both participants with post-traumatic stress symptoms, or those without but were exposed to traumatic stimuli. That is to say, all participants who were exposed to trauma rated the intensity of their recall via imaginal exposure to be less intense when they had a distractor task.
- This effect of intensity reduction was moderated by the complexity of the distractor task. That is to say, the more complicated or cognitively taxing the distractor task was, the less intensive the recalled memories felt.
- In studies involving participants with PTSD, there was a larger decrease in self-reported symptoms among those in the dual taxation condition than in controls. That is to say, participants with PTSD who had imaginal exposure with dual taxation made greater improvements than those without.
- In two studies that included a follow-up, the effects of dual taxation appeared to disappear over time, in as short as 24 hours. That is to say, while distractor tasks reduced the intensity of experiences during imaginal exposure, the benefits were relatively short-lived.
- One study which included functional magnetic resonance imaging (fMRI) found decreased activation in the right amygdala and rostral anterior cingulate cortex (ACC) in dual taxation condition. That is to say, participants who had imaginal exposure to traumatic memories with a distractor task experienced less neurobiological activation in the brain regions that were associated with fear and anxiety, experiences which form part of the core symptoms of distress in PTSD. However, it should be noted that the single fMRI study only included 8 participants, which was an extremely small sample. Thus, findings should be interpreted with caution, and regarded as tentative.
Conclusion
Based on the systematic review, it appears that evidence in support of the dual taxation hypothesis is growing. Of note however, is the presence of some small studies showing that dual taxation + exposure conditions resulted in better improvements alone. If exposure (imaginal and prolonged) is the key mechanism of action that ultimately reduces the effects of PTSD, one would expect there to be no significant difference between conditions. However, that was not the case.
One possible reason that could explain the discrepancy could be due to the reconstructive nature of memories. Studies from cognitive neuroscience have shown that memories are dynamic and constantly undergo a process of reconsolidation. That means they get activated, recalled (retrieved), changed, and re-remembered (reconsolidated). This process often leads to memories being vulnerable to distortions and manipulation, such as in the case of false memories. While this process is particularly concerning in the justice system, the same process might be therapeutically beneficial. Memories which were once unpleasant and intense, could potentially be reconsolidated into one that is less disruptive and intense, with the right therapeutic procedure. The use of dual taxation might then play a role in helping clients reconsolidate distressing memories as less distressing with each repetition, allowing that fear to gradually extinguish.
Another possible reason for the observed difference could be due to the fact that aversive memories are challenging, and participants might consciously or subconsciously avoid recalling them in full, thereby reducing the therapeutic effect of prolonged imaginal exposure. Simply put, as participants in dual taxation conditions experience their recalled memories less intensely, they might be more likely to follow through with the process. In contrast, participants in the recall-only condition might experience their memories very intensely, and engage in ad-hoc coping strategies like avoidance and mind wandering (thinking of something else) instead of engaging in the exposure thoroughly, thereby diminishing the therapeutic effects.
Until more research is done in this area to shed light on the exact reason, an answer will remain elusive for now.
Nonetheless, research findings by Wadji and colleagues is promising in that clinicians working with trauma can now potentially devise novel protocols and procedures to treat traumatic memories through the use of dual taxation tasks. This opens up possibilities involving the use of games (e.g. tetris) or other fun activities that might increase motivation and lower the emotional barriers to treatment. With that, I hope that the attrition rate in trauma treatment will further decrease, and outcomes improve. For everyone else, I hope that this article continue to build upon your understanding of EMDR as psychotherapy.
Until my next review.
Eugene
Blue. Psychological Services 
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