  We describe a multichannel magnetoencephalography (MEG) system that uses
optically pumped magnetometers (OPMs) to sense the magnetic fields of the human
brain. The system consists of an array of 20 OPM channels conforming to the
human subject's head, a person-sized magnetic shield containing the array and
the human subject, a laser system to drive the OPM array, and various control
and data acquisitions systems. We conducted two MEG experiments: auditory
evoked magnetic field (AEF) and somatosensory evoked magnetic field (SEF), on
three healthy male subjects, using both our OPM array and a 306-channel
Elekta-Neuromag superconducting quantum interference device (SQUID) MEG system.
The described OPM array measures the tangential components of the magnetic
field as opposed to the radial component measured by all SQUID-based MEG
systems. Herein we compare the results of the OPM- and SQUID-based MEG systems
on the auditory and somatosensory data recorded in the same individuals on both
systems.
