Localization of Visual Cortex with Coregistered Functional Magnetic Resonance Imaging, Bioelectrically Modeled Cortical Visual Evoked Potential, and Transcranial Magnetic Stimulation Induced Visual Suppression

Abstract:
This study localizes visual stimulus processing using coregistered functional magnetic resonance imaging (fMRI), bioelectrically modeled cortical visual event-related potential (vERP) distribution, and transcranial magnetic stimulation (TMS) induced visual suppression in a single subject. Lateralized vERPs and fMRI activiations were elicited with letters presented to the right and left of fixation. Lateralized TMS induced visual suppression was assessed by errors in reporting portions of letter trigrams. The cortical distribution of the vERP was calculated using an inverse finite-element technique on an anatomically accuate conductivity model constructed from the subject's tissue-type segmented (skin, bone, white matter, gray matter, cerebrospinal fluid) MRI. Electrode locations were magnetically digitized and TMS locations were optically digitized. Coregistration was achieved by fitting the digitized facial contours with the MRI face reconstruction. The location of fMRI activations, the vERP cortical field distribution, and the effective TMS sites were mapped on a 3D model of the cortical surface extracted from the MRI, illustrating the contralateral distribution of visual stimulus reception in secondary visual cortex.