Shapiro (1993, 1995, 2001) calls the model that guides the use of EMDR the adaptive information processing (AIP) model. She emphasises that it is just that - a model - and may be modified in the light of further experimental and clinical findings. The model uses the terminology of neuro-physiological information processing introduced by Bower (1981) and Lang (1979). The model begins by suggesting that there appears to be an innate and adaptive neurologically based information processing system within all of us that allows experience to be used constructively by the individual in an integrative way. However, with severe psychological trauma, an imbalance occurs in the nervous system caused possibly by changes in neuro-transmitters and hormonal changes. The result is that the information acquired from the trauma is not adaptively processed but is maintained within the system neurologically in all its disturbing state. This disturbing material can then be triggered by a variety of internal and external cues, resulting in the well-known symptoms of post traumatic stress disorder, such as flashbacks, nightmares and hyper-vigilance.
Shapiro suggests that under the AIP model, the procedural elements of EMDR stimulate a neuro-physiological process that facilitates information processing. The mechanism by which this activation of facilitation occurs may include:
• An effect of the client's dual focusing of attention as he simultaneously attends to the present stimuli and the past trauma.
• Changes in the neurological state of the brain, caused perhaps by the effects of neuronal bursts or the induction of a neurobiological state similar to that of REM sleep.
• De-conditioning caused by a relaxation response.
It is suggested that, with each set of bilateral stimulation, disturbing information is moved at an accelerated rate further along the appropriate neuro-physiological pathways until it is adaptively resolved.
Shapiro posits both a psychological and a neurobiological basis for accelerated information processing as a result of bilateral stimulation. The psychological explanation, she suggests, is related to dual attention focusing: 'Specifically, the information processing mechanism may be activated when attention is elicited by, or focused on, the external cues. The simultaneous focus on the traumatic memory may cause the activated system to process the dysfunctionally stored material' (Shapiro, 2001). Dual attention focusing as an important facilitator of EMDR effectiveness is given extra support by Lee et al. (2006).
The neurobiological explanation relates to her own hypothesis and those of others (such as Stickgold, 2002) that the eye movements themselves may induce an altered brain state that modifies the behaviour of the information processing system and that other rhythmical movements or repeated stimulation could have similar effects (auditory and tactile).
The theory also incorporates the concept of 'memory networks', which are a series of channels where related memories, thoughts, images, emotions and sensations are stored and linked to one another. In EMDR each channel is 'cleaned out' by reprocessing all the dysfunctionally stored material connected to the traumatic target (or 'node'). The reprocessing is done during each set of eye movements (or other stimulae), where images, thoughts and emotions complete a shift in their progress towards greater therapeutic resolution. Shapiro argues that there are a number of critical elements to the AIP model:
• That traumatic material is represented by dysfunctional information that is physiologically stored and that can be accessed and transformed. She argues that this is consistent with other researchers' views on, for example, declarative and non-declarative memory (Brewin, 1989; Brewin, Dalgleish & Joseph, 1996; Stickgold, 2002). Shapiro suggests that after EMDR traumatic memories may shift from being held primarily and dysfunctionally in non-declarative memory to appropriate storage in declarative memory. Certainly, work by Van der Kolk, Burbridge & Susuki (1997) using position emission topography (PET) scanning of the brains of PTSD patients before and after three sessions of EMDR shows the marked asymmetry in lateralisation of the traumatised brains appears to be corrected and it is suggested that these changes reflect a more realistic differentiation between real and perceived threat, and the reduction in hyper-vigilance.
• The second element is an information processing system that is intrinsic and adaptive. This belief is the basis of EMDR's client-centred model, which assumes that the client's shifting cognitions and affect during EMDR treatment will move optimally with minimal therapist intrusion.
• Concomitant with the transformation in disturbing information in EMDR is a shift in cognitive structure and self-reference. This leads spontaneously to new more self-enhancing behaviours.
• A final element is that the AIP model and the EMDR procedure produce rapidity in the transformation of disturbing traumatic material generally in much less time than has been traditionally thought. Shapiro (2001) suggests that 77 % to 90 % of civilian PTSD is eliminated within three 90 minute sessions.
A number of authors have speculated further and elaborated on the possible theoretical basis of EMDR, including McCulloch & Feldman (1996), Armstrong & Vaughan (1996) ('facilitation of an investigatory/orienting response'), Bergman (1995) ('re-synchronisation of hemispheric activity'), Stickgold (2002) ('the induction of a neuro-biological state similar to REM sleep optimally configured to support cortical integration of traumatic memories into general semantic networks').
Sweet (1995), building on the work of Foa and her colleagues, suggests that several areas are critical to emotional processing: exposure to the traumatic fear ('the conditioned stimulus'); the fear/arousal response; the cognitive or meaning aspects of the experience to be activated - all preferably to be activated simultaneously; moreover, corrective physiological and cognitive information must be introduced, leading to habituation and re-attribution. Sweet found EMDR alone amongst therapies reviewed to contain all these elements.
Hyer & Brandsma (1997) suggest that EMDR works because it involves the curative components of other packages in one package. Lipke (1996) sets out the stages in the EMDR procedure, highlighting the influence of already known therapeutic activities, but also pointing out the unique arrangement of these activities in EMDR: Boudewyns & Hyer (1996) suggest that the EMDR procedure contains five components of therapy necessary for change. Firstly, EMDR is a non-directive and phenomenological method. Secondly, it emphasises movement of information or processing. Successful information processing results in adaptive integration of previously held information and emotions as new or associated information is accessed in a process that has been labelled 'desensitisation using free association'. Thirdly, the clients are facilitated in becoming their own observers of their experiences as they make contact with the trauma - strengthening the observing ego - a kind of mindfulness. Fourthly, an important position is given to cognition by highlighting negative and positive anchoring cognitions. Cognitive reattribution is a vital part of EMDR processing, together with affective and physiological habituation and shift. Fifth is the 'now' processing, with the emphasis on affect and sensations.
Welch & Beere (2002) synthesise neurobiological and psychological explanations for EMDR's effectiveness. The authors set out three interrelated hypotheses with predictions stemming from their model. Firstly, they suggest that EMDR both intensifies and reduces arousal - that EMDR is a 'mood state activator'. The process by which this occurs is explained by the other two hypotheses. The second hypothesis is that the bilateral movements in EMDR lead to bilateral stimulation of the cerebral hemispheres, and here the authors point out that much research has demonstrated lateralisation effects in PTSD. This bilateral stimulation facilitates a reconnection of the two hemispheres. The third hypothesis is that the constricted and avoidant attention in PTSD sufferers is altered through the EMDR procedure, allowing the patient to begin attending to the internal processing of the trauma.
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