How Does Eye Movement Desensitization and Reprocessing Therapy Work? A Systematic Review on Suggested Mechanisms of Action.
Ramon Landin-Romero, R., Moreno-Alcazar, A. ,Pagani , M., Amann, B. (2018).
Frontiers in Psychology

From EMD to EMDR: the standard EMDR therapy protocol

EMDR is a structured eight-phase approach using standardized procedures to address the past, present, and future aspects of a traumatic memory. The traumatic memory is composed of a set of multi-sensory images, negative cognitions, negative emotions, and related unpleasant physical sensations. The EMDR therapy standard protocol includes the following preparation steps. These are: 1) History and treatment plan 2) Preparation phase with an introduction to the EMDR protocol and development of coping strategies 3) An assessment phase with visualization of an image of the traumatic incident, identification of beliefs, and emotions associated with the disturbing event, rating of disturbance recalling the traumatic incident, and rating the validity of preferred cognitions of the client. 4) The desensitization and reprocessing. The client focuses on a dual attention stimulus, while holding in mind the image, thoughts and/or sensations associated with the disturbing memory Following each brief set of bilateral stimulation, the client is asked to identify the associative information that was elicited. 5) Incorporate and strengthen a positive cognition to replace the negative cognition associated with the trauma 6) The body scan to reprocess any remaining bodily sensations. 7)  The client is guided through relaxation techniques designed to re-establish emotional stability if distress has been experienced, and for use between sessions. 8) Re-evaluation, identifying outcomes from the prior session

The completion of EMDR requires attention, self-consciousness, autobiographical semantic memory, and metacognition to successfully identify the potential dysfunctional processes underlying the traumatic memory.

Evidence for the efficacy of EMDR in PTSD and other comorbid disorders

EMDR is recognized as a treatment for PTSD.

The adaptive information processing model

The adaptive information processing model postulates that humans have an innate information processing system that assimilates new experiences and stores them into existing memory networks in an adaptive state. These networks link the thoughts, images, emotions, and sensations associated with experiences. According to the model, pathology arises when new information is inadequately processes and then stored in a maladaptive mode in the memory networks, along with associated distorted thoughts, sensations and emotions.

External stimulation similar to the adverse experience can trigger sensations and images from the traumatic event so that the person re-experiences feelings or bodily sensations. If these memories remain unprocessed, they become the basis of the symptoms of PTSD. When the memories are adequately processed, symptoms can be eliminated and integrated. EMDR can assist in processing the traumatic memories, and different forms of bilateral stimulation would facilitate this processing.

Controversies surrounding EMDR therapy

Other bilateral tactile taps are also effective methods or reducing vividness in trauma.

Discussion

Psychological models

Classical conditioning: orienting and relaxation responses

The orienting response is a natural reflex that can occur with any novel environmental stimulus and procedures a specific set of changes that increase readiness to respond to danger. In the absence of danger, this initial response is rapidly replaced with a feeling of relaxation. According to some authors, this relaxation holds the potential to desensitize the traumatic memory, supressing its associated disturbance.

MacCullock proposed a theory whereby the dual attention task provoked by the eye movements, serves to trigger an oriental response. This orienting response pairs an adaptive explorative response with clinically induced unpleasant memories to remove their negative effect.

The working memory account

The multicomponent model of working memory proposes a ‘central executive’ system responsible for the integration and coordination of information stored in different slave subsystems. During EMDR sessions, memories are held in the visuospatial sketchpad. The dual task draw on the limited-capacity of the visuospatial sketchpad and central executive working memory resources. The competition in resources will impair imagery, and as such, the disturbing images would become less emotional and vivid. The degradation of a traumatic image held in working memory provides patients with a healthy sense of distance form a traumatic event.

Psychophysiological models

Physiological changes associated with the orienting response

Heart rate and galavanic skin response decreased over a set of eye movements. Eye movements are accompanied by changes in respiratory patterns, consistent with a relaxation response.

REM sleep

The rhythmic, multi-saccadic eye movements in EMDR might work as a brain-inhibitory mechanism to reduce anxiety when associated with the traumatic memory, in the same way the material surfacing during dreaming is desensitized by rapid eye movement (REM).

According to the REM hypothesis, the eye movements in EMDR would induce a similar brain state that occurring during REM sleep. REM sleep serves a number of adaptive functions, including memory consolidation via the integration of emotionally charged autobiographical memories into general sematic networks. EMDR would promote the reorganization of the traumatic memories, reducing the strength of the traumatic episodic memories that are mediated by the hippocampus and the associated negative emotion processed by the amygdala.

The authors speculated that the improvements observed after treatment where mediated by an EMDR-driven reduction of the sympathetic activation and suggested that EMDR played a role in restoring normal sleep patterns and lowering the probability of developing PTSD after a traumatic event.

Slow-wave sleep has a key role in memory consolidation and in the reorganization of distant functional networks, and leads to weakening of traumatic memories and reconsolidation of new information.

Neurobiological models

Neurobiological models that can be used to examine changes after intervention with EMDR and other psychotherapies .

Changes in interhemispheric connectivity

Some researchers have speculated that the eye movements in EMDR facilitate associative memory processing and episodic memory retrieval through increased interhemispheric communication via the corpus callosum.

Neural integration and thalamic binding model

The thalamus is centrally involved in the integration of perceptual, somatosensory, memorial, and cognitive processes. The thalamo-cortical binding model serves as a theory for the integration of sensory information and it is supported by neuroimaging studies that consistently find decreases in thalamic activity in PTSD.

Bilateral stimulation might facilitate the subsequent activation of the ventrolateral and central lateral thalamic nuclei via the activation of the lateral cerebellum. The activation of this circuitry is hypothesized to facilitate the integration of somatosensory, memory, cognitive, emotional, and synchronized hemispheric functions that are disrupted in PTSD.

Auditory, visual and tactile bilateral stimulation might facilitate the simulation of thalamocingulate tracts. This would lead to the deactivation of the ventral (affective)  anterior cingulate gyrus, which would enable the reciprocal inhibition of the dorsal (cognitive) anterior cingulate gyrus, which would result in increased cognitive control over overacting affective processing systems and to the reduction of emotional distress.

Structural and functional brain changes associated with EMDR therapy

There is decreased gray matter density in several limbic and paralytic regions in patients who don’t respond to EMDR.

After EMDR treatment, patients showed increases in bilateral hippocampal volume.

The anterior cingulate gyrus and the left frontal lobe facilitate the distinction between real threats and traumatic memories that are no longer relevant to current experience.

Successful EMDER therapy increases prefrontal control over hyperactive limbic subsystems.

Eye movements are associated with decreases in blood flow in the lateral prefrontal cortex. The effectiveness of EMDR might be associated with the reduction of lateral prefrontal cortex over activation during trauma-related recall.

Default mode network might dysfunction in several severe mental disorders.