engleski

Multi-source modeling in magnetoencephalography: Simulation and empirical studies

Measurements of weak neuromagnetic fields provide the real-time monitoring of human brain functions in a noninvasive fashion. However, localization of the electric currents which give rise to the extracranial magnetic fields requires modeling assumptions in order to estimate the solution of the ''ill-posed'' biomagnetic inverse problem. The ability of MEG techniques to identify multiple sources active at a single instant in time and over a time interval, was examined by simulation and empirical studies. Numerical simulation studies examined the effects of: 1) source modeling assumptions (i.e., number of assumed dipoles) ; 2) actual source parameters ; and 3) measurements errors on the resolution of simultaneously active multiple neuromagnetic sources and accuracy and precision of the estimated parameters. Alternative statistical approaches were also evaluated for the assessment of model adequacy and determination of model order. These simulations helped to define the limits of spatial resolution and procedures for analyzing simulated as well as empirical data. When the procedures were applied to empirical visual data, three distinct cortical regions were identified (striate, occipito-temporal, and occipito-parietal). Shifts in source locations within the region identified, associated with changes in the location of the stimulus in the visual field, suggested topographic organization. These results represent the first noninvasive demonstration of retinotopic organization within extrastriate areas of human visual cortex.

magnetoecephalography (MEG); multi-source resolution; spatio-temporal source localization; biomagnetic inverse problem; human visual cortex; striate and exttrastriate retinotopy; selective visual attention; numerical simulations

Istraživanja uključena u ovu doktorsku radnju su u cijelosti napravljena i radnja napisana u Biophysics Group P-6, Physics Division, Los Alamos National Laboratory, Los Alamos, New Mexico, USA. Radnja je predana na ocjenu i obranjenja na Fizičkom odsjeku Prirodoslovno-matematičkog fakulteta Sveučilišta u Zagrebu. Radnja je u Los Alamos National Laboratory izdana kao Dissertation LA-UR-93-195