Anatomical Congruence of Metabolic and Electromagnetic Activation Signals during a Self-Paced Motor Task: A Combined PET–MEG Study

We have investigated the degree of spatial correlation between the cerebral blood flow variations measured by positron emission tomography (PET) and the electromagnetic sources as measured by magnetoencephalography (MEG) in five subjects while performing a self-paced right index finger tapping task. Data were processed independently for each technique using both single-case and intersubject analysis. PET and MEG were coregistered with anatomical magnetic resonance images for each subject. Both extension and flexion motor-related fields were extracted from the MEG signal. Using the single dipole model we identified the motor evoked field 1 (MEF1) in all subjects and the motor field (MF) in three subjects. Individual and intersubject averaged PET data showed consistent contralateral primary sensorimotor (PSM) hand area and bilateral supplementary motor area activation. MEG individual and intersubject averaged results demonstrated that both MEF1 and MF dipoles were localized within the PSM PET activated area. Individual PSM mass center to dipole distance was 12 and 15.3 mm on average for the MEF1 and the MF component, respectively. For the same components, the intersubject averaged analysis shows distances between the PETZ-score maximum and the dipole locations of 6.3 and 15.0 mm, respectively. These results show that PET and MEG MEF1 activation signals spatially coincide within instrumental, registration, and modeling errors.