Biomagnetic Measurements and Stimulation for Imaging and Estimation of the Functional Organization of the Human Brain

Two techniques in magnetics, magnetoencephalography (MEG) and magnetic brain stimulation, have made it possible in recent years to better understand the functional organization of the brain. The first part of this paper focuses on the detection and estimation of MEG activities in human subjects by means of a SQUID system. We have measured MEG activities in normal subjects during sleep and waking stages, and we have obtained more accurate information about sources of K-complexes and delta waves than obtained by electrical measurements alone. The latter part of the study focuses on magnetic stimulation of the brain. We have developed a method of focal and vectorial magnetic stimulation of the brain. The basic idea is to concentrate induced eddy currents locally in the vicinity of a target by a pair of opposing pulsed magnetic fields. Using this method, we were able to stimulate the human cortex within a 5-mm resolution.