Why Bilateral Stimulation Works
The honest answer: we do not know for certain. There are several well-supported theories, and the research is ongoing. The evidence base is substantial — decades of controlled trials and a large body of clinical data consistently support its effectiveness — though the precise mechanism remains under investigation.
Here are the leading explanations.
The most empirically supported explanation. When you hold a distressing memory in mind while simultaneously tracking bilateral stimulation (eye movements, taps, tones), you are taxing working memory. Working memory has limited capacity. Dividing it between the memory and the BLS task reduces the vividness and emotional intensity of the memory.
Bilateral stimulation — particularly eye movements — resembles the rapid eye movements of REM sleep. The brain’s natural memory consolidation and emotional processing happens during REM. EMDR may be activating a similar process artificially — allowing the brain to do what it would have done during sleep if the experience had not been too overwhelming.
Alternating stimulation may promote communication between the brain’s hemispheres — left (verbal, analytical) and right (emotional, somatic). Traumatic memories are often stored in a predominantly right-hemisphere, non-verbal form. EMDR may support integration across hemispheres, allowing the verbal/analytical brain to come online for material that was previously inaccessible to it.
Over repeated sets, the memory becomes less vivid, less emotionally charged — the emotional charge diminishes. This is measurable, replicable, and does not require accepting any particular neurological mechanism.
In this program, we use bilateral stimulation for stabilisation only — strengthening Calm Place, building positive resources. We do not use it for trauma processing without clinical oversight. The mechanism is the same; what differs is the material being held in mind and the intensity of what gets activated.
Research on BLS mechanisms
The working memory explanation has the strongest empirical support. See Gunter & Bodner (2008) and Maxfield et al. (2008) for experimental work on eye movements and memory vividness. The REM analogy was proposed by Stickgold (2002) and remains influential though debated. For a comprehensive review of proposed mechanisms, see Lee & Cuijpers (2013), who conducted a meta-analysis specifically on the contribution of eye movements in EMDR.