It’s not the shimmy, it’s the shift: Differential effects of valence shift type and stimulation mode during a simulated EMDR session in PTSD patients and healthy controls

ABSTRACT Introduction Mechanism-of-action studies on Eye Movement Desensitization and Reprocessing have so far focused mainly on the presumed active component of bilateral stimulation (BLS). In this pilot study, a further potential working mechanism was examined for the first time, involving stimulation-induced changes in emotional valence. Methods Twenty-five patients with posttraumatic stress disorder and 25 healthy controls between 19 and 64 years of age underwent a simulated intervention based on components of Eye Movement Desensitization and Reprocessing (EMDR). Each participant was presented with 18 individual script pairs, simulating different valence shifts (valence switch into neutral, valence switch into positive, no valence shift), whereas BLS vs. no BLS were applied. During the intervention, subjective and physiological emotional responses were measured. Results When valence shifted to positive or neutral, a significant change in treatment-relevant subjective and physiological effect measures was found compared to scripts without a valence shift. For stimulation type, no subjective, but significant physiological effects were observed: The controls showed a physiological de-arousal under BLS, indicated by a decreased skin conductance level, and the patients showed an accelerated heart rate and an increased M. zygomaticus activity. Significant interaction effects were observed: Under BLS, the arousal-reducing and valence-changing effects of negative to neutral switches increased. Interestingly, these BLS effects became conscious to the participants only when valence switches were applied. Discussion The findings provide new insights into the potential emotion-modulating physiological effects of BLS and its interplay with changes in emotional valence.