Biology:Bilateral stimulation

Bilateral stimulation is the use of visual, auditory, or tactile external stimuli occurring in a rhythmic side-to-side pattern. It is a core element of eye movement desensitization and reprocessing (EMDR) therapy, a common treatment for post traumatic stress disorder (PTSD). While the client thinks about distressing memories and feelings, the therapist uses external stimuli to facilitate bilateral stimulation. The treatment originally used only left-to-right eye movements as the bilateral stimulus but other forms of stimuli, often physical vibration in combination with binaural sounds, are now commonly being used as alternatives.

Proponents of EMDR therapy hypothesize that bilateral stimulation assists clients in the processing of painful or traumatizing memories.

Role of Bilateral Stimulation in EMDR

Bilateral stimulation is one of the key components in EMDR. In the most common form of treatment, the client focuses on a traumatic memory and the negative thoughts or feelings associated with that memory. The client then follows with their eyes while the therapist moves their finger or some other object in front of them from left to right. Alternatively, the therapist may choose to use other types of bilateral stimuli. The hypothesis is that doing this allows the client to access and reprocess negative memories, eventually leading to decreased psychological arousal associated with the memory. Therapy then focuses on fostering a positive belief or emotion in the client.

Types of bilateral stimulation

Eye movements are the main form of bilateral stimulation used for EMDR. Originally EMDR used only visual stimuli and the resulting eye movements to facilitate the therapy process. The creator of EMDR therapy, Francine Shapiro, postulated that eye movements in particular were a necessary part of the treatment. However, research found similar efficacy using other types of stimulation and other stimuli are now commonly used by EMDR practitioners. These alternative stimuli include auditory stimuli that alternate between left and right speakers or headphones, and physical stimuli such as tapping of the therapist’s hands.

Bilateral Stimulation Theories

There are various theories as to the mechanisms that make bilateral stimulation effective.

The classical view of EMDR is that bilateral stimulation is a necessary part of the treatment. According to Shapiro, bilateral stimulation may work because it improves the processing of 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.

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 of information they can retrieve about the trauma is limited, and thus the resulting negative emotions are less intense.