Trauma shoves a mind into overdrive. The brain tries to block out fragments of disaster: the spray of shattered glass as one car slammed into another, the smell of smoke. People with post-traumatic stress disorder sometimes constrict their lives, avoiding streets, odors, or songs that make them think about what they’ve experienced. But memories are known — in nightmares, flashbacks, and intrusive thoughts.

Since PTSD was first included in the Diagnostic and Statistical Manual of Mental Disorders in 1980, clinicians have identified a handful of therapies that help people cope with traumatic memories. Over the past decade, a seemingly unconventional treatment has wedged into mainstream therapy.

Eye movement desensitization and reprocessing therapy, or EMDR, might look bizarre to an observer. The practice involves coaxing people to process traumatic memories while simultaneously interacting with images, sounds, or sensations that activate both sides of the brain. Patients might flit their eyes back and forth, following a therapist’s finger, or stare at bursts of light on alternating sides of a screen. The idea is to anchor the brain in the current moment as a patient recalls the past.

n recent years, EMDR has attracted more attention, thanks partly to increased demand for trauma treatment throughout the pandemic and celebrities who have shared their experiences. Prince Harry filmed an EMDR session for a documentary series with Oprah. Sandra Bullock said she turned to EMDR after a stalker broke into her home in 2014; “The Good Place” actress Jameela Jamil wrote in a 2019 Instagram post that EMDR “saved my life.”

Patients seeking EMDR may be inspired by another source: “The Body Keeps the Score,” a seminal book on trauma that has stayed on the New York Times best-seller list for over 200 weeks. Bessel van der Kolk, the book’s author, touts the treatment as one of the most effective ways to combat PTSD symptoms. “It’s not an innovative treatment anymore,” he said. “It’s very well-established.”

What is EMDR?

The psychologist Francine Shapiro developed EMDR in 1987 as she grappled with her disturbing memory — first, experimenting on herself, flitting her eyes back and forth as she walked through a park, and then gradually expanding the treatment to other people.

Therapists carry out EMDR in eight phases that typically unfold over six to 12 sessions, although that number varies from person to person. Each session tends to last between 60 and 90 minutes. First, a therapist will discuss the patient’s current challenges, gather information about their history, and then propose a treatment plan, said Deborah Korn, a clinician and co-author of “Every Memory Deserves Respect.”

She said the patient may need to “float back” from their current symptoms, exploring a recent emotional outburst or panic attack to isolate the triggers that provoked it. The goal is identifying a traumatic memory a patient can work through in the later EMDR phases.

“Most people don’t show up saying, ‘I want to work on my traumatic memories from ages 5 to 11,’“ Dr. Korn said. “They say, ‘I’m miserable.’“

Then, the patient and clinician devise coping strategies, like breathing exercises or meditation to help combat dissociation, that patients can use if they become distressed during or between sessions.

Once those strategies are established, typically after one or two sessions, the therapist instructs the patient to recall the most challenging aspect of the traumatic event. It could be an image, sound, or smell that intrudes on their thoughts most often; for some patients, the most vivid memory related to a trauma occurred just before an event transpired, said Sanne Houben, a researcher at Maastricht University who studies EMDR.

Patients focus on the sensations and emotions they experience while thinking about this aspect as they engage in activities like moving their eyes, tapping their bodies, or hearing a faint beeping sound alternating between their ears. Each set of these bilateral stimulations typically lasts between 30 and 60 seconds.

Periodically, the therapist will ask the patient what they notice or feel, encouraging them to consider the memory from a present-day perspective. “If you say, ‘It’s all my fault,’ a therapist might ask how old were you, did you think you could protect yourself as a child?” said Vaile Wright, the senior director of health care innovation at the American Psychological Association. “It’s not just that you sit there and think about the memory.”

How does EMDR work?

Pushing a patient to revisit the past deliberately isn’t a feature of just EMDR; most therapies for PTSD, including prolonged exposure and cognitive processing therapy, prompt patients to “actively go toward the trauma,” said Dr. Shaili Jain, a PTSD specialist at Stanford University.

Revisiting trauma can activate the body’s stress response — cortisol levels spike, and heart rate jumps. But over time, the process can gradually desensitize you to your memories, habituating your body to the stress and anxiety you experience when confronted with a reminder of the trauma.

“That fight or flight response just gets brought down several notches, so you’re back in the driver's seat of your life,” Dr. Jain said. “Instead of ricocheting off triggers.”

With EMDR, the added component of bilateral stimulation theoretically anchors the patient in the current moment as they engage with a trauma. “We use the phrase: one foot in the present, and one foot in the past,” said Marianne Silva, a clinical social worker, and EMDR practitioner at the VA New England Healthcare System.

The bilateral stimulation must be compelling enough to distract patients but not so overwhelming that they focus on it. Multiplication tables, for instance, would require too much effort, said Richard McNally, a psychology professor at Harvard University.

Dr. Houben said, our brains cannot entirely focus on bilateral stimulation and traumatic memory. The theory behind EMDR is that memories become less vivid and emotional when a patient can’t focus on them entirely.

“At the end of a therapy session, you put it back in storage,” Dr. McNally said. “It’s in a degraded form. It’s not quite as emotionally evocative.”

Is EMDR effective?

Today, clinicians generally consider EMDR an effective trauma treatment. The World Health Organization and American Psychological Association have recommended it for people with PTSD and have issued guidelines for administering medicine. In England, the National Institute for Health and Care Excellence, a rigorous authority in the psychological field, lists EMDR as a tool for adults grappling with trauma and children who have not responded to trauma-focused cognitive behavioral therapy.

But scientists are debating whether EMDR is more effective than other trauma treatment methods. Pim Cuijpers, a professor of clinical psychology at the Vrije Universiteit Amsterdam, analyzed nearly 80 studies on EMDR and found that, while the research pointed to the treatment’s positive effects, “the quality of research is terrible,” he said.

He said many psychological treatments lack rigorous studies, but the evidence for EMDR was fragile, with small sample sizes and potential bias by clinicians conducting the research.

While EMDR is most likely effective, Dr. Cuijpers said, he cautioned against wholeheartedly endorsing the evidence behind the treatment.

And there are very few studies that show EMDR works in the long-term, said Henry Otgaar, a researcher and professor of forensic psychology at Maastricht University in the Netherlands.

Dr. Otgaar, Dr. Houben, and other researchers are investigating whether EMDR increases a patient’s susceptibility to false memories. While creating false memories is a risk in many therapies, Dr. Houben said, "it'sI too early to say if that’s inherent to EMDR.”

When EMDR started becoming more widely publicized in the late 90s and early 2000s, Dr. McNally, then a trauma researcher, was one of the most outspoken critics against the treatment — writing that EMDR was “merely one of the many therapeutic fuzz-balls that litter the landscape of psychology today,” in an issue of the Journal of Anxiety Disorders. He acknowledged that EMDR could desensitize people to their memories but did not think there was convincing evidence that the most distinctive feature of the therapy — the eye movements — had any additional benefit. Today, the issue of whether processing trauma with a therapist would lead to similar results remains debatable; Dr. Jain calls it “the multimillion-dollar question.”

Still, Dr. Jain said that some patients and clinicians swear by the treatment — and enough “solid data” to back it. Patients report fewer PTSD symptoms after sessions, Dr. Wright said, with more occasional flashbacks and intrusive thoughts.

Who could EMDR work for?

“Anybody who has experienced trauma” could benefit from EMDR, said Trisha Miller, a psychotherapist at the Cleveland Clinic. People with mental health conditions beyond PTSD, like depression, eating disorders, phobias, and addictions, may also benefit from EMDR, she added. However, there is not yet robust research confirming that the treatment is effective for those conditions.

People seeking EMDR practitioners should find a certified specialist, Ms. Miller stressed. The EMDR International Association, which runs certification and training for the therapy, keeps a directory of practitioners trained and certified by the organization.

“From a clinician’s perspective, I’m like, ‘whatever works,’“ Dr. Jain said. “If EMDR works for you, do it.”