The authors demonstrate detection and mapping of brain magnetic fields evoked by auditory stimulation with a noncryogenic magnetometer based on spin precession of potassium atoms in spin-exchange-relaxation-free regime. Optical readout using a photodiode array allows flexibility in detector placement while using common elements for most components of the multichannel system. Absence of a cryogenic dewar eliminates magnetic Johnson noise from radiation shields and allows the use of a compact magnetic shield with a high shielding factor. The magnetometer sensitivity is currently equal to 3.5 fT/ Hz 1/2 at 10 Hz, similar to superconducting quantum interference device magnetoencephalography systems.

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