The story of biomagnetism didn’t end with that one experiment, of course. The next step was for David to tell the world what he and Zimmerman had achieved. In the early days of the new decade, he wrote a paper announcing their success. “Jim happily reviewed it and agreed to be co-author,” David wrote in his 2004 retrospective. “In my enthusiasm, I also included Edelsack’s name, as the facilitator.”
The publication of the paper, in 1970, was a watershed moment. Nearly 20 years later, in 1989, the journal Science described it as the ‘birth’ of biomagnetism, citing the interdisciplinary appeal of the technology, which led to the emergence of a new field and a new community of researchers encompassing physicists and psychologists, epidemiologists and computer scientists. “The main point,” David wrote in 2004, “was that a new physics system (SQUID plus shielded room) was now available for a new, low-noise type of measurement, so that biomagnetism now had a reason to grow.”
And grow it did, not least through David’s own work. In the first years of the 1970s, he and his group at MIT reported the first clear direct current (DC) signal from the heart, the first clear signal from skeletal muscle and, “more dramatically,” he says, the first clear MEG signal over the head. Next, he turned his attention to the lungs, exploring the “dust clearance rate” in the lungs of normal subjects vs. those of a small group of smokers (ultimately revealing a possible mechanism of lung cancer in smokers, and thus incurring the wrath of the tobacco industry).
Even as David continued his development of MEG, other labs were also advancing the technique. In 1971, for example, Zimmerman built the first SQUID gradiometer, enabling biomagnetic measurements without shielding. In Finland, in about 1972, Toivo Katila and his group started exploring the potential of the technology. By 1974, they had produced the first fetal magnetocardiogram (MCG). Also by then, David had measured magnetic particles in the lung.
In August 1976, David and his group organized the first “Biomag” conference, with 23 attendees from the U.S., Canada, Finland, France and Japan representing the burgeoning biomagnetism community. Discussions at the workshop mostly centered on instrumentation and measurements of the heart. Only four or five of the attendees were directly interested in the brain, in part because of the technical challenges associated with measuring the magnetic signals associated with brain activity.
“The trouble was,” David says now, with respect to those challenges, “using the SQUID at only one location over the head wasn’t too useful. What we needed was a magnetic map over the entire head.” To this end, in the late 1970s, manufacturers working in the MEG space began to develop multi-SQUID MEG systems. By the mid-1980s, the first commercial multichannel systems were introduced. Instruments enabling whole-head measurements with the technology were constructed in the early 1990s.
This, in turn, prompted researchers to tackle the inverse problem: how to determine the location of electrical neural activity based on the magnetic signals recorded using MEG. Members of the burgeoning community of MEG researchers in several countries launched a concerted—and ultimately successful—effort to solve the inverse problem, allowing studies of many phenomena in the brain. Thus MEG finally came into its own as a means of revealing new information in the brain.
In the decades since, MEG has also been introduced into clinical care. It is most widely used today for both presurgical evaluation and surgical planning in epilepsy patients: for localizing epileptic discharges, determining the language-dominant hemisphere, and more. But other applications are emerging.
Clinicians are exploring, for example, the potential of the technique to aid in the diagnosis of schizophrenia. Historically, such diagnosis was based on clinical assessment and evaluation of patients’ self-reported experiences, especially as their symptoms become more evident over time. As a more objective measure, MEG could offer a means to identify biological markers of the disease. Applications in autism and traumatic brain injury (TBI) are also on the horizon.
The usefulness of the MEG lies in the fact that it sees less than the EEG does, but sees it more accurately. (See Figure 15 below.)
David has kept quite busy himself.
In the early 2000s, Finnish researchers Matti Hämäläinen and Seppo Ahlfors moved to the Athinoula A. Martinos Center for Biomedical Imaging at Massachusetts General Hospital in Boston as part of an endeavor to launch an MEG program—adding to the center’s pioneering efforts in multimodal imaging. To build the shielded room for their MEG system, they enlisted none other than David Cohen, PhD, recently retired from MIT. Joining the Martinos Center’s faculty as an associate professor at Harvard Medical School, David oversaw construction of the room and, in the years and decades that followed, helped steer the direction of the MEG program.
In 2018, the Martinos Center recognized David’s contributions to the center and his foundational role as the “father of MEG” by renaming the Center’s advanced MEG facility the David Cohen MEG Laboratory. The rechristened facility honored an extraordinary career in biomagnetism, a career that now spanned 70 years and a few months, dating back to when he entered the graduate program at the University of California, Berkeley, in the fall of 1948.
Today, at 97 years old, David still plays an active role in advancing the field of study he launched more than half a century ago. Not least: In 2022, he established the David Cohen (DC) Biomagnetism Fellowship. This five-year postdoctoral program supports MEG researchers in developing experimental and analytical tools to measure ultra-low-frequency or direct current (DC) magnetic fields originating in the body—and in applying those tools to basic science and clinical research studies of neurological, psychiatric or other disorders.
It’s a long way from tinkering with crystal set radios in a basement workshop in an immigrant community in Winnipeg. And yet, it’s not a long way at all. David identified early in life an interest in the principles of magnetism and hasn’t stopped pursuing this interest—this passion—in the nine decades and counting since.
Parents who could not understand his desire to pursue science. Struggles with feeling unprepared for the coursework in graduate school. The higher-ups at Argonne deciding not to fund his seemingly fanciful but ultimately fruitful ideas. And academic antagonists denying him tenure at the University of Illinois. These and any number of other challenges and setbacks might have derailed him, convinced him to give up once and for all the study of biomagnetism. But he never did.
He kept looking forward, even after, at age 42, he successfully demonstrated the potential of measuring biomagnetism with a SQUID and a shielded room, and in the process launched a new field of study, the full significance of which, for both science and medicine, has yet to be felt. Well more than 50 years later, the field—and David’s impact—only continue to grow.
