David Cohen (physicist)

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David Cohen was a physicist who helped start biomagnetism, the study of magnetic fields produced by the body. He was born in Winnipeg, Canada, to immigrant parents and earned a BA from the University of Manitoba. He then did graduate work at UC Berkeley, earning a PhD in experimental nuclear physics. While working with large magnets, he became interested in measuring extremely weak magnetic fields from the body, such as those from the heart and brain.

In 1963 Cohen proposed using a magnetically shielded room to block out external magnetic noise, similar to shielding used in nuclear experiments. The first measurements of the heart’s magnetic field (the magnetocardiogram, MCG) and the brain’s magnetic field (the magnetoencephalogram, MEG) were noisy. Cohen built a modest shielded room at first, and later, in 1969, created a much better shielded chamber at MIT. He teamed up with James Zimmerman, who had developed a very sensitive detector called the SQUID. Placing a SQUID in the shielded room produced clear heart signals and enabled the first clear MEG measurements. This work launched the modern era of biomagnetism and inspired other laboratories to start similar studies.

Today, most biomagnetic work focuses on MEG of the brain. Measurements are done in shielded rooms with a helmet holding hundreds of SQUID sensors. There are about 200 MEG systems worldwide. Cohen continued to contribute to the field, authoring many papers, and is often called the father of MEG. He has been a faculty member at Harvard Medical School and has mentored the MEG group at MIT’s Martinos Center at Massachusetts General Hospital.