What is Bilateral Stimulation (BLS), and why is it important in EMDR?
If you've been researching EMDR therapy, you've probably come across the term bilateral stimulation. Bilateral stimulation, or BLS, is the eye movements, tapping, or sounds used in EMDR. While this seems unique and maybe a little strange, I’ve watched it play a role in shifting what years of talk therapy couldn’t. As an EMDRIA Certified therapist with over 25 years of clinical experience, I use bilateral stimulation in every EMDR reprocessing session. Here I share what bilateral stimulation is, why it works, and what you should know if you’re considering EMDR therapy for yourself.
What Are the Different Types of Bilateral Stimulation?
Bilateral stimulation, or BLS, refers to any form of sensory input that alternates from one side of the body to the other. Left, right, left, right. Francine Shapiro, the founder and developer of EMDR, originally got the idea when she was on a walk in 1987. She noticed that as she walked and paid attention to the rhythmic patterns of her footsteps, a distressing thought that had been on her mind became less bothersome to her. This was the origin of EMDR (originally called EMD, or Eye Movement Desensitization), and BLS was an integral piece from the very start.
While there are many variations on BLS, in EMDR therapy, it typically looks like one of three things:
Eye movements. You follow a moving dot, a light bar, or your therapist’s fingers back and forth across your screen or visual field. This is the most commonly known form of BLS, and the one that gave EMDR its name, Eye Movement Desensitization and Reprocessing.
Tapping. You tap alternately on your knees, your shoulders, your thighs, or even on an object such as the desk in front of you. You can do the tapping yourself, or with the help of handheld tappers that vibrate gently from side to side. One popular version of tapping that I use quite a bit in my practice is called the Butterfly Hug (Artigas, 1998), where you cross your arms over your chest and gently tap on the sides of your chest, or shoulders.
Audio tones. You listen through headphones to a tone that alternates from ear to ear.
All three accomplish the same thing: alternating stimulation from the left side of the body to the right. The method we use is largely a matter of personal preference and what feels most comfortable for you.
Why Does Bilateral Stimulation Work?
While researchers are still working to fully understand the mechanisms behind BLS, there are several compelling theories as to why it works.
The Working Memory Hypothesis
The Working Memory Hypothesis suggests that engaging in bilateral stimulation while holding a distressing memory in mind taxes your working memory—the mental system that holds information in the short term. When your brain is occupied with tracking the left-right movement, it has fewer resources available to process the memory with the same emotional intensity. The memory becomes less vivid, less charged, and easier to work with. In short, the BLS is providing just the right level of distraction to keep “one foot in the present, one foot in the past.” You’re focused enough on the past memory to activate it and move through the trauma, but distracted enough that you don’t become emotionally overwhelmed, or flooded, by slipping too deeply into the memory (Van den Hout, Muris, Salemink, & Kindt, 2001).
The Orienting Response Theory
The Orienting Response Theory proposes that the rhythmic back-and-forth movement mimics the natural eye movements we make when scanning our environment for safety. This activates a calming response in the nervous system, similar to what happens when we feel safe enough to look around and take in our surroundings (Armstrong & Vaughan, 1996).
The REM Sleep Hypothesis
The REM Sleep Hypothesis posits the idea that eye movements used in EMDR closely resemble the rapid eye movements that occur during REM sleep, the stage of sleep associated with memory consolidation, and emotional processing. This is also, not surprisingly, the stage of sleep in which dreams happen. Since dreams are widely understood to be a mechanism for the brain to process and make sense of your experiences and thoughts, this theory makes a lot of sense. Some researchers believe BLS may activate a similar process, helping the brain integrate and make meaning of difficult experiences in a way it does naturally during sleep (Stickgold, 2002).
Can You Do EMDR Without BLS?
Yes and no. To do EMDR without BLS is essentially to provide talk therapy. What we know from decades of research is that EMDR with bilateral stimulation is more effective than EMDR without it, and that, when administered properly, EMDR produces measurable changes in how the brain stores traumatic memories.
What Does BLS Feel Like?
In my experience, I’ve found that most of the people I’ve worked with tend to find bilateral stimulation surprisingly calming. The rhythmic quality often has a grounding effect, giving your body something predictable to follow while your mind does the deeper work.
Some people have a strong preference for one type of BLS over another. I've worked with clients who find eye movements too distracting and prefer tapping. Others love the headphone tones because it feels more contained. There's no right answer, and we'll figure out together what works best for you.
Does Bilateral Stimulation Work Online?
Virtual EMDR works, and bilateral stimulation translates well online. In sessions with my clients, I use a browser-based BLS tool that displays a moving dot on your screen, while I control the speed of the dot and the duration of each set of BLS from my computer. I also have the option of adding in audio tones that can be delivered through your headphones. Alternately, tapping can be self-directed with simple guidance. Since I opened my private practice in 2019, I’ve offered exclusively virtual sessions, and have watched countless clients find deep healing through EMDR, all using online forms of bilateral stimulation. Virtual EMDR works, and it works well.
The Bottom Line on BLS
Bilateral stimulation is a core component of EMDR, and provides an integral piece of the puzzle for trauma resolution through this modality. EMDR’s specific blend of focusing on the memory, and what you think and feel when focusing on the memory, combined with BLS, allows your brain to process stuck memories in a way that talk therapy alone can't access.
If you’d like to learn more about BLS and EMDR, reach out to schedule a free consultation call where we can discuss your needs and whether EMDR may be the right path for you.
Susan Candiloro, LCSW-R, is an EMDRIA Certified Therapist and EMDRIA Approved Consultant offering virtual therapy in New York and Florida. With over 25 years of experience in the mental health field, Susan specializes in working with women navigating trauma, anxiety, perfectionism, and late-diagnosed ADHD. Interested in working with Susan? Reach out here.