ABSTRACT
The neural activity of the brain generates electrical currents that, in accord with general physical laws, can be monitored outside the head by means of their resulting electrical and magnetic fields. The corresponding recordings are known as the electroencephalogram (EEG) and magnetoencephalogram (MEG), respectively. Whereas EEG recordings have been used for many years to evaluate clinical conditions such as epilepsy, the technologies that permit MEG recordings to be made are relatively recent. Due to the intrinsic noise present in the sensors and amplifiers used to obtain MEG records, only the relatively strong fields produced by the simultaneous firing of large ensembles of similarly oriented neurons can be detected.
