Reliability and validity of neuroelectric source imaging in primary somatosensory cortex of human upper limb amputees

The present study investigated the test-retest reliability of EEG source localizations of somatosensory evoked potentials (SEPs) in human upper limb amputees over a long time frame (several months) and examined the validity of source reconstruction. In two sessions spaced several months apart five unilateral upper limb amputees were stimulated at the first and fifth digit of the intact hand and at the left and right lower corner of the mouth. To examine the validity of the results of the neuroelectric source reconstruction a comparison with neuromagnetic source localization was performed for two subjects. The source localizations of the SEP components were found to be highly reproducible: the mean standard deviation of the dipole locations was 8.80 mm in the x-, 7.00 mm in the y- and 4.15 mm in the z-direction. The match of the comparison of EEG and MEG data was in the range of one centimeter. These results 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 in upper limb amputees and suggest high stability of cortical reorganization in these subjects.