RESUMO
A new method is described to calculate epicortical potential fields from scalp fields based on linear algebra. It requires detailed anatomical information, for each subject, obtained from MR images. The calculation is validated in a physical model of the human head and applied to human subjects. The results suggest that the method yields reliable epicortical fields that help to localize evoked cortical activity in humans.
Assuntos
Encéfalo/fisiologia , Potenciais Evocados Visuais/fisiologia , Couro Cabeludo/fisiologia , Encéfalo/anatomia & histologia , Eletroencefalografia , Humanos , Imageamento por Ressonância Magnética , Modelos NeurológicosRESUMO
The performance of two methods, used to localize brain activity from evoked potential fields measured on the scalp, was assessed in a tank model of the human head. This physical model contained a human skull encased in a polymer simulating the resistivity and geometry of brain and scalp. The dipole localization method mislocalized the positions of known dipole sources by several centimeters. The mislocalization was systematic. The dipoles were localized too deeply in the head. The Laplacian method yielded a field resembling the brain surface field (epicortical potential field) provided that the iso-potential contours of the scalp field closed within the measurement range. Clipping resulted in a serious mislocalization of the position of the peak of the epicortical potential field.
Assuntos
Mapeamento Encefálico/métodos , Potenciais Evocados Visuais/fisiologia , Estimulação Elétrica , Humanos , Modelos Anatômicos , Couro Cabeludo/fisiologiaRESUMO
Potential fields on the surface of the brain were estimated from discretely sampled scalp fields in human subjects. Relatively simple methods of linear algebra were combined with detailed anatomical information from magnetic resonance imaging. The method was verified using a tank model of the human head that encased a fully hydrated human skull in a polymer matrix of controlled resistivity matching that of human brain and scalp. Brain surface fields evoked by checkerboard contrast reversal, spread less than their scalp field counterparts, and provided information helpful in localizing brain activity.