Eye movement desensitization and reprocessing (EMDR) is an effective treatment for alleviating PTSD symptoms. In EMDR, the patient recalls traumatic memories while simultaneously making horizontal eye movements. There are three hypotheses as to why and how EMDR works:

1. EMDR works by recalling aversive memories and eye movements are not necessary
   This states that prolonged exposure as a result of the traumatic memories leads to the positive results of EMDR (e.g. imaginal exposure therapy). However, research shows that eye movements do have an additive effect.
2. EMDR works by stimulating “interhemispheric communication”
   This states that eye movements increase communication between left and right brain hemispheres. This is believed to enhance the ability to remember an aversive event while not being negatively aroused. This indicates that the stimulus does not matter as long as it is left and right. However, vertical eye movements are also effective, meaning that this hypothesis is disputed.
3. EMDR works by taxing the working memory
   This states that recalling an emotional memory while taxing the working memory makes the memory less emotional because the working model has less capacity for the memory.

During recall, a memory becomes labile (i.e. events during recall influence how the memory is reconsolidated). The imagination inflation effect states that attempting to form a vivid and realistic image during recall influences the original memory. This makes the memory more vivid and realistic. The imagination deflation effect may occur by taxing the working memory while recalling the memory.

Eye movements thus tax working memory and make sure that the traumatic memory is reconsolidated less vividly (i.e. working memory theory). This can also reduce the impact of flashforwards and flashbacks. Other tasks that task the working memory are also effective (e.g. mental arithmetic). EMDR may be useful in treating other disorders as many disorders are activated by a negative event. However, the evidence for this is sparse.

There is an inverted U when it comes to the effectiveness of increasing working memory load. The competition between the recall of the traumatic memory and distracting tasks decreases the vividness and emotionality of the memory. This means that the tax on the working memory should not be too great. People who have a stronger delay on a reaction time task when they make eye movements improve more as a result of EMDR. This means that people with lower working memory capacity benefit more from EMDR.

Clinicians appear to increasingly use tones in the right and left ear instead of eye movements with EMDR. This is based on the interhemispheric communication hypothesis and patient preferences. However, there is no clear evidence as to whether this is effective. It is less effective than eye movements.

Mindfulness-based treatments may be effective for the treatment of PTSD. These treatments make use of mindful breathing. This taxes working memory to the same extent as eye movements, making it effective for the same reasons that EMDR is effective.