Differences between Meg

The electrical sources in the brain not only produce an electric potential on the scalp, but also a magnetic field over the head (Cohen 1972). A recording of the potential is the well-known electroencephalogram (EEG), while a recording of the magnetic field is relatively new and is called the magnetoencephalogram (MEG). Although the MEG and EEG are produced by the same sources, an MEG map over the head shows a different spatial pattern than does an EEG map. These differences in the pattern may be useful, since they may allow the MEG to provide new information about the sources. Mostly for this reason, an increasing number of MEGs are being recorded (reviewed by Reite and Zimmerman 1978, and by Williamson and Kanfman 1981). Some of these recordings do suggest pattern differences which are useful; for example, they suggest that the MEG can better localize a source. However, these data are not conclusive. Theoretical studies have also been made which address these differences (Cuffin and Cohen 1979; Romani et al. 1982a). These studies, too, indicate useful differences. They predict pattern differences which, if true in actual recordings, would allow the MEG to better localize and differentiate the neural sources, in some ways, than does the EEG. The purpose of this work is to perform a test and see if these predicted differences can be experimentally demonstrated. Demonstration is needed because the theoretical studies are based on spherical models of the head, and it is not