Abstracts

Rationale: To identify the similarities in the spatial spectra of the cortical surface with the 2-D spatial spectra of the scalp EEG.Methods: The spatial power density (PSDx) of the cortical surface in a brain model of an adult male subject was computed with two dimensional (2-D) fast Fourier transform (FFT). The voxel resolution in the model was 2x2x3.2 mm. The slice thickness was 3.2 mm and the in plane resolution was 2x2 mm. The model was built from segmented MR images. The electrical activity was modeled with distributed dipolar sources confined to the top portion of the cortex above the eyebrow circle. The resulting scalp potentials were calculated with a finite element model of the head. The PSDx of the simulated EEGs was also calculated with the 2-D FFT.Results: There were broad peaks present in the 2-D plots of the PSDx of the cortex and EEGs. These were mainly in the frequency range of 0.15 to 0.5 cycles/cm. This could be due to gyri structures of 1-3 cm width on the cortical surface.Conclusions: These results suggest that information was present in the EEG at the spatial frequencies of gyri. This also suggests that the Nyquist frequency for sampling the scalp EEG should be 3.0 cycles/cm and an optimal interelectrode spacing of 3.0 mm is desirable for extraction of cortical information from scalp EEG in humans.