Bilateral stimulation: differential effects in EEG and peripheral physiology

BACKGROUND: Bilateral sensory stimulation (BLS), such as eye movements or alternating tactile stimulation, is a key component of Eye Movement Desensitisation and Reprocessing (EMDR), a recommended treatment for post-traumatic stress disorder (PTSD). However, the neurophysiological mechanisms underlying BLS remain poorly understood. AIMS: This study examined the physiological effects of visual and tactile BLS on frontal electroencephalography (EEG) activity and autonomic arousal in patients with PTSD and healthy controls, by varying the type of stimulation in different emotional stimuli. METHOD: Twenty female PTSD patients and twenty matched healthy controls participated in a counterbalanced, within-subjects design. Participants recalled a subjectively stressful or neutral event while receiving visual or tactile BLS. Frontal EEG and peripheral psychophysiological measures were recorded before and after stimulation. Data were analysed using mixed model analysis to examine the effects of stimulation type, memory condition and group. RESULTS: Both visual and tactile BLS significantly increased the total power of frontal EEG and decreased spectral edge frequency and peripheral physiological activation. These effects were consistent between the groups and memory conditions. CONCLUSIONS: BLS, regardless of visual or tactile modality or emotional memory content, is associated with increased frontal EEG activity and reduced autonomic arousal. These findings support the hypothesis that BLS facilitates top-down cortical regulation, potentially aiding emotional processing in EMDR by using an inherent mechanism to promote psychological recovery. More research is needed to clarify the neural mechanisms and clinical implications.