INTRAOPERATIVE LOCALIZATION OF SENSORIMOTOR CORTEX BY CORTICAL SOMATOSENSORY-EVOKED POTENTIALS - FROM ANALYSIS OF WAVE-FORMS TO DIPOLE SOURCE MODELING

Intra-operative localization of sensorimotor cortex is of increasing i mportance as neurosurgical techniques allow safe and accurate removal of lesions around the central sulcus. Although direct cortical recordi ngs of somatosensory evoked potentials (SEPs) are known to be helpful for cortical localization, source localization models can provide more precise estimates than subjective visual analysis. In addition to int ra-operative analysis of waveforms and amplitudes of SEPs to median ne rve stimulation in 20 neurosurgical patients, we used a spatiotemporal dipole model to determine the location of the equivalent dipoles cons istent with the cortical distribution of the SEPs. The early cortical SEPs were modeled by 2 equivalent dipoles located in the postcentral g yrus. The first dipole was primarily tangentially oriented and explain ed N20 and P20 peaks. The second dipole was primarily radially oriente d and explained P25 activity. We found consistent localization of the first dipole in the postcentral gyrus, which was always located within 8 mm of the central sulcus, with an average distance of 3 mm. This fi nding provides an objective basis for using the SEP phase reversal met hod for cortical localization. We conclude that dipole source modeling of the cortical SEPs can be considered as an objective way of localiz ing the cortical hand sensory area.