MEG COVARIANCE DIFFERENCE ANALYSIS - A METHOD TO EXTRACT TARGET SOURCE ACTIVITIES BY USING TASK AND CONTROL MEASUREMENTS

A method is proposed for extracting target dipole-source activities fr om two sets of evoked magnetoencephalographic (MEG) data, one measured using task stimuli and the other using control stimuli, The differenc e matrix between the two covariance matrices obtained from these two m easurements is calculated, and a procedure similar to the MEG-multiple signal classification (MUSIC) algorithm is applied to this difference matrix to extract the target dipole-source configuration, This config uration corresponds to the source-configuration difference between the two measurements, Computer simulation verified the validity of the pr oposed method, The method was applied to actual evoked-field data obta ined from simulated task-and-control experiments, In these measurement s, a combination of auditory and somatosensory stimuli was used as the task stimulus and the somatosensory stimulus alone was used as the co ntrol stimulus, The proposed covariance difference analysis successful ly extracted the target auditory source and eliminated the disturbance from the somatosensory sources.