Source current estimation of brain magnetic field evoked by mental rotation task using minimum-norm method with MUSIC prescanning

In this study, a dynamic estimation of the current distribution in a mental rotation task from the measurements of the brain magnetic field was presented. The authors used a current reconstruction algorithm based on the weighted minimum-norm estimation (WMNE) with the weighing factors calculated from the results of simplified multiple signal classification (MUSIC) scan. In this method, in addition to the depth normalisation technique, weighting factors of the WMNE are determined by the cost value distribution previously calculated by the MUSIC scan which contains the temporal information of the measured data. This method is able to handle the noisy data without introducing large distortion into the source estimation, and is also able to suppress the large estimation error related to the temporal correlation of the multiple source activation. Source current distributions in the mental rotation and the control tasks were estimated from the magnetoencephalographic (MEG) signals for five subjects in the latency range between 100 and 250 ms after the stimulus onset. Activation of the right lateral posterior temporal region about 200 ms was observed in 3 out of 5 subjects in the mental rotation task, while only the primary visual cortex was activated continuously up to about 200 ms in the control task.