REDUCTION OF BRAIN NOISE INFLUENCE IN EVOKED NEUROMAGNETIC SOURCE LOCALIZATION USING NOISE SPATIAL CORRELATION

In magnetoencephalographic measurements, magnetic fields caused by spo ntaneous brain activities not related to the neural activities under s tudy are often referred to as brain noise. This is because the accurac y in neural source localization is considerably degraded by such spont aneous neuromagnetic fields. This paper reports the experimental resul ts of applying the previously proposed noise covariance method to redu cing the degradation caused by brain noise and to improving the accura cy in localizing auditory-evoked neural sources. Firstly we present th e results of our experiments using measured brain noise and computer-g enerated signal fields. These results confirm that the covariance meth od can, in principle, improve the accuracy of evoked neural source loc alization. Next, the method was applied to source localization for act ual neuromagnetic fields evoked by speech sounds. The results obtained strongly suggest that the method is effective in processing actual ev oked neuromagnetic data.