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Abstract:
Abstract: The ideal brain imaging technique would provide
high resolution information both spatially and temporally. Dipole
source localization (DSL) using visual evoked potentials (VEPs)
offers millisecond temporal resolution, but poor spatial
resolution. Functional magnetic resonance imaging (fMRI) offers
millimeter spatial resolution, but poor temporal resolution. The
present study evaluates a new DSL method by comparing estimated
dipole locations and orientations to the corresponding fMRI
sources. VEPs were recorded at 49 scalp electrode sites over the
occipital pole while subjects viewed an m-sequence modulated mosaic
of 60 reversing checkerboards. A spherical head model was used for
DSL whereby source location, direction, magnitude and temporal
waveform were calculated for each stimulus patch using a new
algorithm that assumes a common time function for common sources.
Structural and functional MRIs were acquired in conjunction with
retinotopic mapping methods developed by Brian Wandells group at
Stanford. The representation of each patch in the VEP stimulus was
then localized on the MRI-generated cortical surface within primary
visual cortex. DSL and fMRI sources were compared in two subjects.
Regions of the visual field were found in which the DSL and fMRI
sources were in close agreement. There were also regions with
minimal agreement. This study shows that a fine-grained connection
between the VEP and fMRI sources is possible.
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