Bilateral stimulation

Bilateral stimulation is a core element of eye movement desensitization and reprocessing (EMDR) therapy, one of the common treatments of post traumatic stress disorder (PTSD). The treatment has the patient think about a traumatic event. While the patient thinks about a traumatic event, the bilateral stimulation is applied.^[1]

While the treatment originally used eye movements as the bilateral stimulus, there are now many other forms of stimuli used as alternatives. There are also many theories for the inner working mechanisms of bilateral stimulation.

Role of Bilateral Stimulation in EMDR

Bilateral stimulation is one of the key components in EMDR. In the main form of the treatment, the patient focuses on a traumatic memory that is connected to their PTSD. While they do this, the therapist moves their finger in front of the patient, and the patient follows with their eyes. These simultaneous tasks allow them to reprocess the memory and better consolidate it.^[2] Other forms of EMDR use different types of eye movements, or a different type stimulus altogether.

Types of bilateral stimulation

When EMDR was first created, it was done with eye movements as the stimulus. The creator, Francine Shapiro, believed that eye movements in particular are a necessary part of the treatment. While Shapiro initially believed eye movements to be an essential part of the therapy, following research found that other forms of stimulation are also effective.^[3] Alternative stimuli include hearing tones, and tapping the therapist’s hands.^[4]

Eye Movements

Eye movements are the main form of bilateral stimulation used for EMDR. Shapiro created EMDR after noticing that eye movements resulted in less intense negative emotions.^[5] The eye movements are typically bilateral and horizontal.

One theory for eye movements is that by taking up resources in the working memory, the traumatic memories are less vivid. It is possible that eye movements make it easier to focus on trauma, and thus enables processing.^[3]

Bilateral Stimulation Theories

The classical view of EMDR is that bilateral stimulation is a necessary part of the treatment. However, it is still unclear whether or not the bilateral stimulation is what causes EMDR to work. According to Shapiro, bilateral stimulation may work because it improves the processing of all emotional information, or it may have a specific effect on traumatic information that has not been integrated and fully processed. One theory is that the dual attention task induces a mental state similar to REM sleep, which helps with reprocessing trauma.^[2]

Another theory holds that bilateral stimulation works by providing a dual task. This results in a physiological state that improves information processing, which may result in information being integrated and the trauma being less intrusive.^[6]

Another theory uses the working memory model, which states that the working memory has limited capacity. By having the patient perform a bilateral stimulation task while retrieving memories of trauma, the amount they can recall the trauma is limited, and thus the resulting negative emotions are less intense.^[5]

References