Comparison of the performance of distributed source estimation in the human brain using normal and vector magnetic field measurements

In neuromagnetism research, it is important to accurately estimate internal electrical sources in the human brain from the spatial and temporal distributions of magnetoencephalogram (MEG) activities over the head. In this study, we compared the performance of distributed internal source estimation in the human brain under two different MEG measurement conditions: (a) measurements of only the normal components of the external magnetic fields and (b) three-dimensional vector measurements of the external magnetic fields. We applied the sub-optimal least-squares subspace scanning source estimation technique to both measurement conditions. The results showed that with measurement of only the normal components, distributed sources tend to be estimated deeper in the brain than they should be, while three-dimensional vector measurements had the potential to provide a better estimation of the depth of the internal source distribution