Reproducibility and stability of neuroelectric source imaging in primary somatosensory cortex

The present study investigated the test-retest reliability of EEG source localization of somatosensory evoked potentials (SEPs) over an extended time period and tested the accuracy of source reconstruction co-registred with individual brain morphology (MRIs). Seven healthy subjects were stimulated pneumatically at the first digit and fifth digit of each hand and at the left and right lower corner of the mouth in two sessions spaced several weeks apart. At each location 1000 stimuli were presented. The overlay of the dipole localizations with the individual anatomic structure of the subjects' cortex was accomplished by the use of magnetic resonance images. A spherical 4-shell model of the head was used to localize the neuroelectric sources of the EEG data. In two cases a more realistically shaped 3 compartment model was computed using the boundary element method (BEM). The source localizations of the SEP component were found to be highly reproducible: the mean standard deviation of the dipole locations was 5.21 mm in the x-, 5.98 mm in the y- and 4.22 mm in the z-direction. BEM was not found to be superior to a 4-shell model. These data support the use of multi-electrode EEG recordings combined with MRI as an adequate method for the investigation of the functional organization of the somatosensory cortex.