3 Things You Didn’t Know About David Cohen and MEG

In 2018, the Martinos Center dedicated its advanced magnetoencephalography facility as the David Cohen MEG Laboratory. David Cohen, the inventor of MEG, a leader in the field of biomagnetism for more than 50 years, and a Martinos Center faculty member who was instrumental in building and developing the facility in question, was on hand to help launch the rechristened lab.

In anticipation of the event, we delved into Cohen’s long, storied life and career, from his early days devising ways to measure the very weak magnetic fields originating in the human body to some of his equally impressive 21st-century accomplishments. Here are three of the many things we learned.

In another life, Cohen was actually a “really strong magnetic field” kind of guy

In 1957, two years after earning his PhD, Cohen joined the Argonne National Laboratory in Illinois, where he worked as an accelerator physicist specializing in strong magnetic fields. While he enjoyed the work, his thoughts kept drifting to another topic. “I have a fancy job doing high-energy physics and working with big magnets,” he says, looking back on those early days. “And for some reason I’m thinking, year in and year out, wouldn’t it be fun to measure very weak magnetic fields”—that is, the kind of fields generated by the human body.

In 1963 a group in Syracuse reported the first measurement of the magnetic field of the human heart. In order to minimize the magnetic disturbances associated with everyday urban life, they had performed the experiments in the middle of a field, far away from the hustle and bustle of the city. Cohen had another idea: instead of escaping background noise, block it out by building a magnetically shielded room.

MEG launched on New Year’s Eve 1969 with a prominent researcher stripped down to his shorts

What better way to celebrate the holiday, right?

By late 1969, Cohen had built a large, shielded room at the Francis Bitter lab at MIT—a pod-like structure with a stairway descending from an open panel on the side, it looked like something out of a science fiction movie—and was using it to measure the weak magnetic fields emanating from the human body. But the detector he had developed wasn’t yielding enough signal. To address this problem, he reached out to researcher James Zimmerman, who had helped introduce the superconducting quantum interference device (SQUID) some five years before. This device could measure extremely weak magnetic fields. It had not yet been shown to work in humans but only because no one had tried.

“Jim arrived near the end of December, complete with SQUID, electronics and nitrogen-shielded glass dewar,” Cohen says. “It took a few days to set up his system in the room, and for Jim to tune the SQUID. Finally, we were ready to look at the easiest biomagnetic signal: the signal from the human heart, because it was large and regular. Jim stripped down to his shorts, and it was his heart that we first looked at.”

Cohen has been recognized by Guinness World Records. Twice.

Though he “retired” in 1993, he has remained a highly productive investigator in the years since: as a visiting scientist at MIT and, since 2001, an associate professor of radiology at the Martinos Center. Today Cohen can look back on a lifetime of accomplishments. Many of these are now inscribed in the dusty, leather-bound tomes of the history of science. But there’s one accomplishment that has largely escaped the attention of the academic community.

In May 2013, Cohen and Sheraz Khan, a Center investigator who works closely with Cohen, reported the magnetic field of the wall of the shielded room in the Center’s MEG facility: an almost unimaginable 0.5 femtotesla/√Hz. (In recording biomagnetism, researchers want to account for any other sources of magnetism that might impact the measurement.) The paper caught the attention of the reference book and website Guinness World Records, which certified the finding as the “weakest magnetic field measured”—a record that still stands today.

This wasn’t the first time Cohen had made the pages of Guinness World Records. In the 1980s the book recognized him for what was then the weakest magnetic field ever measured: a field of 8 x 10-15 tesla, measured in the shielded room at the Francis Bitter lab at MIT. It was quite the accomplishment, recording such a weak signal. But of course, in 2013, as so many times over the six decades plus of his research career, David Cohen outdid himself.

David Cohen and his magnetically shielded room in 1969