Eye movement desensitization and reprocessing (EMDR) therapy has been shown by empirical studies to be effective in relief from psychological traumas including posttraumatic stress disorder (PTSD). Several logical concepts regarding the origin of the EMDR effect have been presented, but no detailed neural explanation is available. This lack of a widely accepted scientific explanation for the EMDR effect has led to skepticism about the therapy by many therapists and potential clients. The authors present evidence based primarily on quantitative electroencephalogram studies that the neural basis for the EMDR effect is depotentiation of fear memory synapses in the amygdala during an evoked brain state similar to that of slow wave sleep. These studies suggest that brain stimulation during EMDR significantly increases the power of a naturally occurring low-frequency rhythm in memory areas of the brain, binding these areas together and causing receptors on the synapses of fear memory traces to be disabled. This mechanical change in the memory trace enables it to be incorporated into the normal memory system without the extreme emotions previously associated with it. EMDR is a medical procedure because it changes the physical structure of the brain to modify problematically stored memories.