Multi-SQUID Recordings of Human Cerebral Magnetic Fields May Give Information about Memory Processes

We have used a very-low-noise 7-channel SQUID magnetometer to record cerebral auditory responses of healthy humans to rare intensity changes in a tone sequence. The frequently presented “standards” triggered a signal with its maximum at 90 ms. The responses to the weaker “deviants” peaked at about 140 ms. This “mismatch field” seems to reflect an automatic reaction of the human brain to stimulus changes and it may be connected with neural processes involved in the sensory memory. The responses seem to be generated by partly overlapping sources in the auditory cortex, the differences between source locations did not exceed 1 cm. This type of source determination has not been possible with electric scalp recordings.