Neuromagnetic SQUID measurement in a superconducting magnetic shield

A superconducting magnetic shield of high-Tc superconductor Bi(Pb)SrCaCuOx has been constructed whose diameter is 65 cm and length is 160 cm respectively. We have successfully observed somatosensory evoked magnetic fields coming out from human brains in the superconducting magnetic shield stimulating the median nerves of patients by current pulses. We made a 64-channel whole-head SQUID magnetometer of SNS (Superconductor/Normal metal/Superconductor) junctions. The sensitivities of the dc-SQUID of mesoscopic SNS junctions are around 5 fT//spl radic/(Hz) even in rather unfavorable surroundings. The magnetic shield can reduce a magnetic field to around -80 dB or 10/sup -4/ even at as low a frequency as 0.05 Hz.