Movement-related desynchronization of the cerebral cortex studied with spatially filtered magnetoencephalography

Event-related desynchronization (ERD) within the a and beta bands on unilat eral index finger extension and hand grasping was investigated on six norma l volunteers with magnetoencephalography (MEG). A novel spatial filtering t echnique for imaging cortical source power, synthetic aperture magnetometry (SAM), was employed for the tomographic demonstration of ERD. SAM source i mage results were transformed into statistical parametric images. On the sa me hand grasping task, a functional MRI (fMRI) study was conducted on two s ubjects and compared with the ERD result. When the MEG data were analyzed w ith the fast Fourier transformation, power attenuation within the alpha and beta bands was evident on the contralateral sensorimotor area just prior t o movement onset. The tomographic distribution of ERD was clearly obtained with SAM statistical imaging analysis. The equivalent current dipole (ECD) for the signal-averaged motor field was localized to the hemisphere contral ateral to the hand movement, roughly at the center of the region displaying beta-band ERD, The signal increase on fMRI roughly colocalized with the ER D on the contralateral sensorimotor area. Ln conclusion, with the novel spa tial filtering technique for the brain magnetic field, SAM, cortical region s contributing to ERD on finger movement were successfully demonstrated in a tomographic manner. The relative colocalization of the contralateral SAM ERD with ECD as well as the fMRI activation suggests that SAM is a practica lly useful technique to extract event-related signals from brain noise. (C) 2000 Academic Press.