[Beginnings of the Development of Magnetoencephalography Systems Using Superconducting and Spintronics Sensors]

Electroencephalography (EEG) and magnetoencephalography (MEG) are the only noninvasive imaging methods of human brain function with temporal resolutions of millisecond-order. MEG has theoretically superior spatial resolution to EEG. However, the weak signal of MEG can only be measured with the superconducting quantum interference device (SQUID). SQUID-MEG equipment has extremely high manufacture and running costs. Moreover, the theoretically high spatial resolution is practically limited by the necessary setback distances between the sensors and scalp, because the Dewar vessel containing liquid helium for the SQUIDs requires a thick vacuum wall. The latest developments in room temperature magnetometers, such as tunnel magnetic resistance (TMR) sensors, may solve the problem of setback distance in MEG scanners. Here I review my personal research history of MEG from the era of single-channel SQUID-MEG to the present era of single-channel TMR-MEG. I also propose the major considerations for the future development of MEG systems.