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Hypothesized Mechanisms of Action

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. There are three different models for conceptualizing the role of the orienting response in EMDR: cognitive/information processing (Andrade, Kavanagh, & Baddeley, 1997; Lipke, 1999), neurobiological (Bergmann, 2000, 2008; Servan-Schreiber, 2000; Stickgold, 2002) and behavioral (Armstrong & Vaughan, 1996; MacCulloch & Feldman, 1996). These models are not exclusive; to some extent, they view the same phenomenon from different perspectives. Barrowcliff, Gray, Freemen, & MacCulloch (2004) posit that the orienting in EMDR is actually an “investigatory reflex,” that results in a basic relaxation response, upon determination that there is no threat; this relaxation contributes to outcome through a process of reciprocal inhibition. Others suggest that the inauguration of an orienting response may disrupt the traumatic memory network, interrupting previous associations to negative emotions, and allowing for the integration of new information.. It is further possible that the orienting response induces neurobiological mechanisms, which facilitate the activation of episodic memories and their integration into cortical semantic memory (Stickgold, 2002). It is additionally possible that EMDR’s sensory stimulation and procedures repair thalamic and thalamo-cortical function, facilitating the repair of maladaptive neural linkage of information processing (Bergmann, 2008). This theory has lately obtained experimental support (Richardson et al., 2009). Further, studies have shown a direct relationship between the orienting response and thalamic activation (Friedman, Goldman, Stern, & Brown, 2009; Menon, Ford, Lim, Glover, & Pfeff erbaum, 1997; Minamimoto & Kimura, 2002), findings that are highly consistent with information processing. Further research is needed to test these hypotheses.

There are several research studies (e.g., Andrade et al., 1997; Kavanaugh, Freese, Andrade, & May , 2001; van den Hout, Muris, Salemink, & Kindt, 2001) indicating that EMs and other stimuli have an effect on perceptions of the targeted memory, decreasing image vividness and associated affect. Two possible mechanisms have been proposed to explain how this effect may contribute to EMDR treatment. Kavanaugh et al. (2001) hypothesize that this effect occurs when EMs disrupt working memory, decreasing vividness, and that this results in decreased emotionality. They further suggest that this effect may contribute to treatment as a “response aid for imaginal exposure” (p. 278), by titrating exposure for those clients who are distressed by memory images and/or affect. Similar hypotheses have been proposed by Lilley et al. (2009), Hout et al. (2010), and van den Hout et al. (2013). Van den Hout et al. (2001) hypothesize that EMs change the somatic perceptions accompanying retrieval, leading to decreased affect, and therefore decreasing vividness. They propose that this effect “may be to temporarily assist patients in recollecting memories that may otherwise appear to be unbearable” (p. 129). This explanation has many similarities to reciprocal inhibition.

The majority of the speculative models can be seen from a theoretical perspective to possibly dovetail with each other. The underlying physiologies of temporal binding, neural mapping, hippocampal remapping, limbic depotentiation, frontal lobe activation, reciprocal ACC suppression, and REM systems activation are sufficiently interrelated with respect to the orienting response and neural systems linkage as to preclude mutual exclusion. Future findings will, undoubtedly, shed increasing light on their interrelationship.

Andrade, J., Kavanagh, D., & Baddeley, A. (1997). Eye-movements and visual imagery: a working memory approach to the treatment of post-traumatic stress disorder. British Journal of Clinical Psychology, 36, 209-223.
- Tested the working memory theory. Eye movements were superior to control conditions in reducing image vividness and emotionality.

Armstrong, M.S., & Vaughan, K. (1996).
An orienting response model of eye movement desensitization. Journal of Behavior Therapy & Experimental Psychiatry, 27, 21-32.

Barrowcliff, A.L., Gray, N.S., Freeman, T.C.A., & MacCulloch, M.J. (2004).
Eye movements reduce the vividness, emotional valence and electrodermal arousal associated with negative autobiographical memories. Journal of Forensic Psychiatry and Psychology, 15(2), 325-345.

Bergmann, U. (2000).
Further thoughts on the neurobiology of EMDR: The role of the cerebellum in accelerated information processing. Traumatology, 6(3), 175-200.

Bergmann, U. (2008). The neurobiology of EMDR: Exploring the thalamus and neural integration. Journal of EMDR Practice and Research, 2(4), 300–314.

 

Friedman, D., Goldman, R., Stern, Y., & Brown, T. (2009). The brain’s orienting response: An event-related functional magnetic resonance imaging investigation. Human Brain Mapping, 30(4), 1144–1154.

 

Hout, M.A., Engelhard, I.M., Smeets, M.A., Hornsveld, H., Hoogeveen, E., and de Heer, E. (2010).

Counting during recall: taxing of working memory and reduced vividness and emotionality of negative memories. Applied Cognitive Psychology, 24(3), 303-311.


Kavanagh, D. J., Freese, S., Andrade, J., & May, J. (2001). Effects of visuospatial tasks on desensitization to emotive memories. British Journal of Clinical Psychology, 40, 267-280.
- Tested the working memory theory. Eye movements were superior to control conditions in reducing within-session image vividness and emotionality.  There was no difference one-week post.


Lilley, S.A., Andrade, J., Turpin, G., Sabin-Farrell, R., & Holmes, E.A. (2009). Visuospatial working memory interference with recollections of trauma. British Journal of clinical psychology, 48 (3), 309-321.

 

Lipke, H. (1999). Comments on "thirty years of behavior therapy..." and the promise of the application of scientific principles. The Behavior Therapist, 22, 11-14.

MacCulloch, M.J., & Feldman, P. (1996).
Eye movement desensitization treatment utilizes the positive visceral element of the investigatory reflex to inhibit the memories of post-traumatic stress disorder: A theoretical anaylsis. British Journal of Psychiatry, 169(5), 571-579. doi:10.1192/bjp.169.5.571

Menon, V., Ford, J. M., Lim, K. O., Glover, G. H., & Pfefferbaum, A. (1997).
Combined event-related fMRIand EEG evidence for temporal-parietal activation during target detection. Neuro  Report, 8, 3029–3037

 

Minamimoto, T., & Kimura, M. (2002). Participation of the thalamic CM-Pf complex in attentional orienting. Journal of Neurophysiology, 87(6), 3090–3101.

 

Richardson, R., Williams, S. R., Hepenstall, S., Gregory, L., McKie, S., & Corrigan, F. (2009). A single-case fMRI study EMDR treatment of a patient with posttraumatic stress disorder. Journal of EMDR Practice and Research, 3(1), 10–23.

Servan-Schreiber, D. (2000). Eye movement desensitization and reprocessing. Is psychiatry missing the point? Psychiatric Times 17(7), 36-40.

Stickgold, R. (2002).
EMDR: A putative neurobiological mechanism of action. Journal of Clinical Psychology, 58, 61-75.


Van den Hout, M., Muris, P., Salemink, E., & Kindt, M. (2001). Autobiographical memories become less vivid and emotional after eye movements. British Journal of Clinical Psychology, 40, 121-130.
- Tested their theory that eye movements change the somatic perceptions accompanying retrieval, leading to decreased affect, and therefore decreasing vividness. Eye movements were superior to control conditions in reducing image vividness. Unlike control conditions, eye movements also decreased emotionality.


Van den Hout, M.A., Eidhorf, M.B., Verboom, J., Little, M., & Engelhard, I.M. (2013). Blurring of

emotional and nonemotional memories by taxing working memory during recall. Cognition and Emotion, doi: 10. 1080/02699931. 2013. 848785.


Bergmann, U. (2010). EMDR's Neurobiological Mechanisms of Action: A Survey of 20 Years of Searching. Journal of EMDR Research and Practice, 4, 22-42.


El Khoury-Malhame, M. et al. (2011).
Attentional bias in post-traumatic stress disorder diminishes after symptom amelioration. Behaviour Research and Therapy 49, 796-801.
- Attentional bias toward aversive cues in PTSD has been hypothesized as being part of the dysfunction causing etiology and maintenance of PTSD. The aim of the present study was to investigate the cognitive strategy underlying attentional bias in PTSD and whether normal cognitive processing is restored after a treatment suppressing core PTSD symptoms.” An average of 4.1 EMDR sessions resulted in remission of PTSD. Post treatment "similarly to controls, EMDR treated patients who were symptom free had null e-Stroop and disengagement indices.


Elofsson, U.O.E., von Scheele, B., Theorell, T., & Sondergaard, H.P. (2008).
Physiological correlates of eye movement desensitization and reprocessing. Journal of Anxiety Disorders, 22, 622-634.
- Changes in heart rate, skin conductance and LF/HF-ratio, finger temperature, breathing frequency, carbon dioxide and oxygen levels were documented during the eye movement condition.  It was concluded the "eye movements during EMDR activate cholinergic and inhibit sympathetic systems. The reactivity has similarities with the pattern during REM sleep.”


Gunter, R. & Bodnar, G. (2009)
. EMDR Works...But How? Recent Progress in the Search for Treatment Mechanisms. Journal of EMDR Practice and Research, 3, 161-168.


Hornsveld, H. K., Landwehr, F., Stein, W., Stomp, M., Smeets, S., & van den Hout, M. A. (2010).
Emotionality of loss-related memories is reduced after recall plus eye movements but not after recall plus music or recall only. Journal of EMDR Practice and Research, 4, 106-112.
- Recall-plus-music was added to investigate whether reductions in emotionality are associated with relaxation. . . Participants reported a greater decline in emotionality and concentration after eye movements in comparison to recall-only and recall-with-music. It is concluded that eye movements are effective when negative memories pertain to loss and grief.


Kapoula Z, Yang Q, Bonnet A, Bourtoire P, & Sandretto J (2010)
. EMDR Effects on Pursuit Eye Movements. PLoS ONE 5(5): e10762. doi:10.1371/journal.pone.0010762
- EMDR treatment of autobiographic worries causing moderate distress resulted in an "increase in the smoothness of pursuit [which] presumably reflects an improvement in the use of visual attention needed to follow the target accurately. Perhaps EMDR reduces distress thereby activating a cholinergic effect known to improve ocular pursuit.


Kristjánsdóttir, K. & Lee, C. M. (2011).
 A comparison of visual versus auditory concurrent tasks on reducing the distress and vividness of aversive autobiographical memories. Journal of EMDR Practice and Research, 5, 34-41.
- Results showed that vividness and emotionality ratings of the memory decreased significantly after eye movement and counting, and that eye movement produced the greatest benefit. Furthermore, eye movement facilitated greater decrease in vividness irrespective of the modality of the memory. Although this is not consistent with the hypothesis from a working memory model of mode-specific effects, it is consistent with a central executive explanation.


Lee, C.W., Taylor, G., & Drummond, P.D. (2006).
The active ingredient in EMDR: Is it traditional exposure or dual focus of attention? Clinical Psychology and Psychotherapy, 13, 97-107.
- This study tested whether the content of participants’ responses during EMDR is similar to that thought to be effective for traditional exposure treatments (reliving), or is more consistent with distancing which would be expected given Shapiro’s proposal of dual focus of attention. Greatest improvement on a measure of PTSD symptoms occurred when the participant processed the trauma in a more detached manner, which indicates the underlying mechanisms of EMDR and exposure therapy are different.


Lilley
, S.A., Andrade, J., Graham Turpin, G.,Sabin-Farrell, R., & Holmes, E.A. (2009). Visuospatial working memory interference with recollections of trauma. British Journal of Clinical Psychology, 48, 309–321.
- Tested patients awaiting PTSD treatment and demonstrated that the eye movement condition had a significant effect on vividness of trauma memory and emotionality compared to counting and exposure only.  In addition, "the counting task had no effect on vividness compared to exposure only, suggesting that the eye-movement task had a specific effect rather than serving as a general distractor” (p. 317)


MacCulloch, M. J., & Feldman, P. (1996).
Eye movement desensitization treatment utilizes the positive visceral element of the investigatory reflex to inhibit the memories of post-traumatic stress disorder: A theoretical analysis. British Journal of Psychiatry, 169, 571–579.
- One of a variety of articles positing an orienting response as a contributing element (see Shapiro, 2001 for comprehensive examination of theories and suggested research parameters).  This theory has received controlled research support (Barrowcliff et al., 2003, 2004).


Pagani, M., et al. (2013)
. Correlates of EMDR Therapy in Functional and Structural Neuroimaging: A Critical Summary of Recent Findings. Journal of EMDR Practice and Research, 7, 29-38.


Propper, R., Pierce, J.P., Geisler, M.W., Christman, S.D., & Bellorado, N. (2007).
Effect of bilateral eye movements on frontal interhemispheric gamma EEG coherence: Implications for EMDR therapy. Journal of Nervous and Mental Disease, 195, 785-788.
- Specifically, the EM manipulation used in the present study, reported previously to facilitate episodic memory, resulted in decreased interhemispheric EEG coherence in anterior prefrontal cortex. Because the gamma band includes the 40 Hz wave that may indicate the active binding of information during the consolidation of long-term memory storage (e.g., Cahn and Polich, 2006), it is particularly notable that the changes in coherence we found are in this band. With regard to PTSD symptoms, it may be that by changing interhemispheric coherence in frontal areas, the EMs used in EMDR foster consolidation of traumatic memories, thereby decreasing the memory intrusions found in this disorder.


Rogers, S., & Silver, S. M. (2002).
Is EMDR an exposure therapy? A review of trauma protocols. Journal of Clinical Psychology, 58, 43-59.
- Theoretical, clinical, and procedural differences referencing two decades of CBT and EMDR research.


Rogers, S., Silver, S., Goss, J., Obenchain, J., Willis, A., & Whitney, R. (1999).
A single session, controlled group study of flooding and eye movement desensitization and reprocessing in treating posttraumatic stress disorder among Vietnam war veterans: Preliminary data. Journal of Anxiety Disorders, 13, 119–130.
- This study was designed as primarily a process report to compare EMDR and exposure therapy.  A different recovery pattern was observed with the EMDR group demonstrating a more rapid decline in self-reported distress.


Sack, M., Hofmann, A., Wizelman, L., & Lempa, W. (2008).
Psychophysiological changes during EMDR and treatment outcome. Journal of EMDR Practice and Research, 2, 239-246
- During-session changes in autonomic tone were investigated in 10 patients suffering from single-trauma PTSD.  Results indicate that information processing during EMDR is followed by during-session decrease in psychophysiological activity, reduced subjective disturbance and reduced stress reactivity to traumatic memory.


Sack, M., Lempa, W. Steinmetz, A., Lamprecht, F. & Hofmann, A. (2008).
Alterations in autonomic tone during trauma exposure using eye movement desensitization and reprocessing (EMDR) - results of a preliminary investigation. Journal of Anxiety Disorders, 22, 1264-1271.
- The psycho-physiological correlates of EMDR were investigated during treatment sessions of trauma patients.  The initiation of the eye movements sets resulted in immediate changes that indicated a pronounced de-arousal.


Servan-Schreiber, D., Schooler, J., Dew, M.A., Carter, C., & Bartone, P. (2006).
EMDR for PTSD: A pilot blinded, randomized study of stimulation type. Psychotherapy and Psychosomatics, 75, 290-297.
- Twenty-one patients with single-event PTSD (average IES: 49.5) received three consecutive sessions of EMDR with three different types of auditory and kinesthetic stimulation.  All were clinically useful.  However, alternating stimulation appeared to confer an additional benefit to the EMDR procedure.


Stickgold, R. (2008).
Sleep-dependent memory processing and EMDR action. Journal of EMDR Practice and Research, 2, 289-299.
- Comprehensive explanations of mechanisms and the potential links to the processes that occur in REM sleep.  Controlled studies have evaluated these theories (see Christman et al., 2003; Kuiken et al. 2001-2002).


Suzuki, A., et al. (2004).
Memory reconsolidation and extinction have distinct temporal and biochemical signatures. Journal of Neuroscience, 24, 4787– 4795.
- The article explores the differences between memory reconsolidation and extinction. This new area of investigation is worthy of additional attention.  Reconsolidation may prove to be the underlying mechanism of EMDR, as opposed to extinction caused by prolonged exposure therapies. "Memory reconsolidation after retrieval may be used to update or integrate new information into long-term memories . . . Brief exposure … seems to trigger a second wave of memory consolidation (reconsolidation), whereas prolonged exposure . . leads to the formation of a new memory that competes with the original memory (extinction).”


van den Hout, M., & Engelhard, I. (2012).
How does EMDR work? Journal of Experimental Psychopathology, 3, 724-738.


van den Hout, M., et al. (2012).
EMDR: Tones inferior to eye movements in the EMDR treatment of PTSD. Behaviour Research and Therapy, 50, 275-79.
- EMs outperformed tones while it remained unclear if tones add to recall only. . . EMs were superior to tones in reducing the emotionality and vividness of trauma memories. [I]n contrast to EMs, tones hardly tax working memory and induce a smaller reduction in emotionality and vividness of aversive memories. Interestingly, patients’ preferences did not follow this pattern: the perceived effectiveness was higher for tones than for EMs. . . . Clearly, the superior effects of EMs on emotionality and vividness of trauma memories were not due to demand characteristics.


Wilson, D., Silver, S. M., Covi, W., & Foster, S. (1996).
Eye movement desensitization and reprocessing: Effectiveness and autonomic correlates. Journal of Behaviour Therapy and Experimental Psychiatry, 27, 219–229.
- Study involving biofeedback equipment has supported the hypothesis that the parasympathetic system is activated by finding that eye movements appeared to cause a compelled relaxation response. More rigorous research with trauma populations is needed.


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