AbstractEye Movement Desensitization and Reprocessing represents a promising approach to treatment of posttraumatic disorders. The specific factors underlying its effectiveness rely particularly on bilateral stimulation, which seems to provoke a specific neurobiological response during traumatic recall particularly in individuals with PTSD. The empirical findings provide evidence for the effect of BLS on autonomic nervous system shifting the balance towards parasympathetic activation (reducing arousal) as well as the effect on subjectively perceived vividness and emotional burden of autobiographic memories (decrease). The most credible hypotheses derive the effects from neurobiological mechanisms employed in dual focus attention, orienting reflex and REM sleep. Further research is needed to explore the processes included in the EMDR therapy in more detail and clarify the role of bilateral stimulation.