Localization of cortical motor areas in humans by magnetoencephalography

: Movement-related MEG activity initiated by voluntary unilateral index finger movement was studied in 16 normal volunteers. Evoked motor field response was obtained by averaging with respect to movement onset detected by the actogram. Group averaging of single dipole solutions for the peak of the readiness field (Bereitschaftspotential) revealed activation of the cortical area corresponding to typical motor representation of the hand. Individual data showed strong individual differences in dipole localization, which may be associated with simultaneous activation of sensorimotor cortical areas. Readiness field obtained from each individual was localized either in the pre- or post-central gyrus. Individual differences in the localization may be related to simultaneous activation of the cortical areas incorporated in the sensorimotor complex. The study demonstrates that single dipole modeling may be used for the localization of the sensorimotor complex, but it is insufficient to separate the activity components of this complex.