Remembering Mark Hallett, leader in transcranial magnetic stimulation

Mark Hallett saw the therapeutic promise of transcranial brain stimulation right from the start. When he opened his lab at Harvard Medical School in 1977, he had a transcranial electrical stimulation device—not yet available in the United States—flown over from the United Kingdom.

He had first seen one the year prior, when he was a fellow studying neurology at the London Institute of Psychiatry, working with pioneers Anthony Barker, an electrical engineer, and John Rothwell, a neurologist. Hallett, who died 2 November, had been fascinated.

In 1985, when Barker and Rothwell created the first and far more comfortable transcranial magnetic stimulation devices, Hallett, then clinical director of the U.S. National Institute of Neurological Disorders and Stroke, procured one of those, too.

In those days, safety protocols were more loosely enforced than they are now. Things were “a bit Wild West,” says neurologist Mark George, who collaborated with Hallett from 1990 to 1996 while on a National Institutes of Health fellowship. “You could do things you couldn’t do now.”

But Hallett and his NINDS colleagues, particularly in Eric Wasserman’s lab, set about creating protocols for the intensity, duration and frequency of current needed to use TMS effectively but safely. In 1992, the Food and Drug Administration and the NIH approved those protocols, and NINDS accelerated its TMS research.

For four years, things rolled along nicely. Then someone in Wasserman’s lab, trying to save time, shortened the intervals between TMS applications in one healthy volunteer. This caused a “very frightening” seizure, Hallett told the “Stimulating Brains” podcast in 2024. The institutional review board shut down the project to investigate. The group was eventually cleared to restart their work, but it took two more seizure cycles before they finally got the protocols right.

Through it all, Hallett guided the anxious, ambitious research teams and the institutional review board through new parameters. “Those seizures could have been a complete show-stopper,” George says. “There’s no doubt in my mind that we would not be doing TMS—I would not be using TMS in the ways I do for depression, for instance—without Mark’s early leadership and pioneering skills in that crisis.”

Hallett is credited with picking up a damaged TMS field and setting it back on its feet. He went on to become what George and many other colleagues consider one of the most productive and foundational leaders in TMS science, while also revolutionizing the study of movement disorders.

“I think he’s one of those rare birds who have been truly essential to two different, independent fields,” George says.

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orn in Philadelphia in 1943, Hallett stood out as a young man: a high school tennis champion, senior class president and drama star, playing a lead role in a school production of “Father of the Bride.” His wife, Judith Peller Hallett, a classics scholar, wrote in a remembrance that Hallett disobeyed his parents only once, by leaving Philadelphia to attend Harvard. Hallett meant to study astronomy there, but when he learned about the work Harvard professors Timothy Leary and Richard Alpert (aka Ram Dass) were doing with psychedelics, he decided the brain could prove even more complex and mysterious than the cosmos. He dropped astronomy for biology.

After graduation, he went on to Harvard Medical School, followed by a neurology residency at Massachusetts General Hospital, a two-year fellowship at the NIH, and, in 1975, a pivotal year at the Institute of Psychiatry, Psychology and Neuroscience in London, where he encountered the brain stimulation field. Hallett returned to Boston to take up an associate professorship at Harvard Medical School and head the new Clinical Neurophysiology Laboratory at Peter Bent Brigham (now Brigham and Women’s) Hospital, where he played a key role in founding the neurological study of functional movement disorders. In 1984, he moved to the Washington, D.C., area to join the new NINDS, setting up his own program, the Human Motor Control Section.

He stayed for almost four decades. In 1994, he and his colleagues published a paper showing that TMS could modulate activity in the motor cortex, and then in 1995 showed that it could improve mood in depression. He published reports in 1997 and 1998 showing TMS’s power to study and induce brain plasticity.

Through this work, says George, Hallett exerted a primary, essential force behind the creation and development of two large and distinct fields: the development of TMS and other brain stimulation technologies, and understanding movement disorders. In the latter field, Hallett’s pioneering use of TMS revolutionized the treatment of functional neurologic disorders, in which people suffer involuntary movements that appear to be voluntary. Doctors tended to receive these patients skeptically, referring to their symptoms as psychogenic movements. Hallett’s use of TMS in the 2000s showed these movements are almost always involuntary, and his insight helped inspire the new functional neurological disorders term and treatment regimens that were evidence based and respectful of patient experience. Along the way, he published more than 1,200 papers.

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allett had two children, Nicholas and Victoria, and also mentored more than 150 NIH fellows from all over the globe. Dozens of his protégés rose to lead high-profile research centers, labs and departments in imaging, movement disorders and the neurology of dystonia, speech and parkinsonism. His colleagues and trainees found him good-natured and bighearted. As one encomium put it, “There was a quiet humility about him—a rare combination of brilliance and warmth that made colleagues, trainees, and patients feel truly heard.”

Hallett loved traveling, particularly with his family. He relished exploring the many cities where he and other researchers convened. “He seemed to know everything about any city we went to,” George recalls. “Not just where to eat, but everything about its history.”

Neurologist Helen Mayberg, who pioneered deep-brain stimulation for depression, got a taste of Hallett’s skills as a tour guide about a decade ago, when she and Hallett were in Paris to review a research program. One afternoon, Hallett invited her to the Louvre. “It was stunning what he knew about painting,” she says. “We spent a good half hour in front of this one painting; he never ran out of things to say about it, and it was all fascinating. I essentially had my own docent.”

In his last few weeks of a year-long battle with glioblastoma, dozens of his trainees and collaborators scheduled video calls to thank him, and to talk with him one more time. Valerie Voon, a neuropsychiatrist who worked alongside Hallett at the NIH from 2004 to 2009, was one of those trainees. Voon is now herself a leader in expanding the use of TMS in neuropsychiatry. Hallett was extremely kind, she says, with an encyclopedic knowledge and deep expertise. But also, she says, he was unflappable, a trait that arose from having confidence not just in himself but in his colleagues and in the power of knowledge.

“He’s most brilliant,” she says, “when something has gone wrong. There’s no anxiety. There’s no stress.”