Neurobiological Correlates of EMDR Monitoring – An EEG Study

The following fascinating study (1)  imaged for the first time the specific brain area activations associated with the therapeutic actions typical of EMDR protocol. The findings suggest that traumatic events are processed at cognitive level following successful EMDR therapy, thus supporting the evidence of distinct neurobiological patterns of brain activations during bilateral ocular stimulation (BS) associated with a significant relief from negative emotional experiences.

“Investigations by positron emission tomography (PET) and single photon emission computed tomography (SPECT) have identified an impairment of the medial prefrontal cortex (mPFC), associated with a hyper-reactivity of the amygdalae, to constitute the core neural correlate of post-traumatic stress disorder (PTSD) [2]. On the other hand, several studies have provided evidence for the clinical efficacy of Eye Movement Desensitization and Reprocessing therapy (EMDR) in the treatment of PTSD [3]. EMDR is an information processing therapy for anxiety disorders that focuses on trauma elaboration or highly stressful recollections [4].

A distinct characteristic of EMDR is the use of alternating bilateral stimulation such as eye movement, tactile or auditory. The patient is asked to focus upon the traumatic memory image while simultaneously attending to an alternate stimulus for brief eye movements (right-left) sets of approximately 30 seconds. As a result EMDR has been included in many international trauma treatment guidelines[5]–[8] and in 2011 has also been shortlisted as evidence-based practice for the treatment of PTSD [9], anxiety and depression symptoms [10].

This Study’s Discussion

The first relevant result of the study was the ability to perform an on-line monitoring of the cortical firing occurring during EMDR therapy by means of the EEG, more specifically during bilateral ocular stimulation. For the first time, maximal brain activations associated with the therapeutic actions envisaged by the EMDR protocol could be outlined and represented on the cortical surface. To the best of our knowledge this is also the first time psychotherapy is monitored and dynamically represented by functional imaging throughout its entire duration. The logistic and technical effectiveness of such complicated methodology carried out by psychotherapists, psychologists, psychiatrists and EEG technicians, all at the same time, provided the opportunity of performing the experiments in a totally patient-friendly environment, i.e. in a comfortable private practice therapy room, avoiding possible biases resulting from physical and psychological discomfort for the patient due to an unfriendly examination environment [28].

Following successful EMDR therapy, the main neurobiological finding of the study was the shift of the maximal cortical firing, during both autobiographic script listening and BS, from prefrontal and limbic regions at T0 to fusiform and visual cortex at T1 (Figure 4 and ​and 5, respectively).

Fig 4

Fig 5.

The significantly higher activation found in patients during the BS at T0 compared to T1 in rPFC (Figure 5) confirms the leftward differences found during the same phase in patients as compared to controls.

Prefrontal activation is associated with evaluation of self-generated material [30] being anterior cingulate cortex the point of integration of emotional information involved in the regulation of affect [31] as well as a key substrate of conscious emotional experience monitoring information with affective consequences. Rostral PFC as part of the limbic system is thought to be involved in processes concerning the emotional value of incoming information and to be critically implicated in functions altered in psychic trauma response. Its activation upon emotional induction is considered to represent the neurobiological correlate of the affective valence of the stimulus [32]. Moreover, episodic memory retrieval is known to activate PFC [33], and a close relationship between autobiographical/episodic memory, the self and the involvement of PFC was described [34]. PFC has also been found to be activated while suppressing unwanted memories [35] and was found by near infrared spectroscopy to be activated during trauma recall before EMDR therapy [36]. All these functions may be exaggerated in patients before EMDR therapy in which the self-referential emotional contents cause an activation in rPFC larger than in normal individuals or in the patients after having processed the traumatic event.

One relevant neurobiological effect of EMDR in patients was represented by the differences found between the cortical activation at T0 as compared to T1 during script listening (Figure 4). In this comparison we found at T1 a significant increase of the EEG signal in right FG as well as in right visual cortex (VC). These changes suggest a better cognitive and sensorial (visual) processing of the traumatic event during the autobiographic reliving after successful EMDR therapy with a preferential activation moving from the emotional fronto-limbic cortex (at T0) towards the associative temporo-occipital cortex (at T1). Once the memory retention of the traumatic event can move from an implicit subcortical to an explicit status different cortical regions participate in processing the experience. On the other hand FG is implicated in the explicit representation of faces, words and abstract thoughts [37] and its prevalent activation after successful EMDR therapy might be associated with an elaboration at higher cognitive level of the images related to the event.

As found in the script analysis, FG showed a higher activation also during BS at T1. Interestingly, in our patients these comparisons showed different outcomes with a clear lateralization towards the left hemisphere during BS (Figure 5) and on the right side during the script listening (Figure 4). According to the emotional asymmetry theory the right hemisphere is dominant over the left for emotional expressions and perception. Furthermore, both hemispheres function as somewhat of a functional unit and an increased activation in one of them will result in an inhibition in the contralateral one. The prominent activation found during BS at T1 in association areas in left hemisphere might then correspond to a cognitive processing of traumatic memories reaching the explicit state after successful EMDR therapy associated to a significant restraint of negative emotional experiences. The left hemisphere has also an important role in explicating emotions and left FG was also found to be activated during tasks implying episodic memory and memory retrieval associated with attentional control [37].

…interregional connectivity changes reported while reliving of the traumatic event, representing the variations in brain activity networking upon different conditions, were found in three cluster pairs. The loss of functional connectivity between left VC and FG found in patients at T1 as compared to T0 during the script listening was associated with the disappearance of symptoms and speaks in favor of disconnection of a pathological visual network after successful EMDR therapy. At this stage, as an effect of successful trauma elaboration, the visual images of the event are processed and stored in primary and associative visual cortex and likely decoupled from the emotional memory of faces and bodies linked to the event, typically processed by FG. Moreover, affectively valenced stimuli were shown to prompt event-related synchronization in posterior brain regions in the theta frequency band [38]. Such synchronization might have disappeared once the images of the traumatic event lost their emotional meaning.

The findings of decreased pair-wise interactions between PFC, ACC and PCC found in patients as compared to controls during BS show that the functional connectivity during trauma relieving and involving three important frontal regions was not present in patients. This underscores the pathological nature of the changes occurring in post-traumatic conditions in the limbic system and the central role of the latter in properly processing negative autobiographical events. Event-related activity in gamma band was observed in healthy volunteers in ACC and left PFC upon exposition to emotional stimuli [39], suggesting that gamma activity in PFC may be modulated by emotional processing in ACC.

A recent theory postulates that traumatic memories are retained in amygdalar synapses due to powerful electric signals overpotentiating alpha-amino-3-hydroxy-5-methyl- 4-isoxazole (AMPA) receptors. During slow wave sleep (SWS) this would prevent their merging with the cognitive memory trace via anterior cingulate cortex (for review see[59]). Animal studies have demonstrated that a low-frequency tetanic stimulation using one to five pulses per second can cause in the synapses of the basolateral tract of the amygdale a depotentiation of AMPA receptors proportional to the stimulation frequency and extinguishing the traumatic memories [61].

Such stimulus is similar to the one administered during EMDR sessions (about 2 Hz) and the pathophysiological mechanism of the therapy might be related to the slowing of the depolarization rate of neurons in the limbic system elicited by BS. This in turn would result in the emotional memories pathologically confined in the amygdale moving to higher brain centers and being fully processed [59]. At macroscopic level, our findings (hyperactivation of parahippocampal gyrus and limbic cortices at T0 in both BS and script listening) seem to support such hypothesis …

According to the Adaptive Information Processing theory [62] when a traumatic event occurs, information processing may be incomplete, probably due to the fact that strong negative feelings or neurobiological reactions interfere with it. This prevents the forging of associative connections of memory with other networks and memory is dysfunctionally stored. During an EMDR session memory distressing components are linked to more adaptive information existing in the neural networks and therefore memory desensitization and reprocessing take place, thus contributing to symptom reduction and ultimately remission.

Our findings point to a highly significant activation shift following EMDR therapy from limbic regions with high emotional valence to cortical regions with higher cognitive and associative valence. This suggests a strong neurobiological rationale of EMDR, thus supporting its efficacy as an evidence- based treatment for trauma.”

References

1. Pagani, M., Di Lorenzo, G., Verardo, A. R., Nicolais, G., Monaco, L., Lauretti, G., … & Siracusano, A. (2012). Neurobiological correlates of EMDR monitoring–an EEG study.