Functional MRI studies rely on detecting hemodynamic changes as revealed by BOLD signals to infer underlying changes in local neuronal activity. The local spatial specificity and resolution are dependent on limitations introduced by non-neuronal factors. LFPs are electrophysiological signals generated by the summed electric currents flowing from populations of neurons within small volumes of nervous tissue around the recording electrode tips, and are considered more direct indicators of neuronal activity. Understanding how BOLD signals are related to electrical activity of neuron populations is essential for the quantitative interpretation of fMRI data. Here, we evaluated the spatial extents of LFPs in functionally distinct areas 3b and 1 of S1 cortex in new world monkeys, using two 49-channel multi-electrode arrays, and in separate experiments we performed fMRI at very high field strength (9.4T) to obtain very high resolution spatial extents of stimulated activations. Images of both modalities were co-registered within 0.10 mm accuracy. We are thereby able to relate fMRI data directly to a ‘gold standard’ electrophysiological measurements LFPs with good sensitivity and spatial resolution. The spatial extents of BOLD and LFP responses of S1 cortex were fitted with Gaussian point spread functions (PSFs). We found that the mean full-width at half maximum (FWHM) of the fitted PSFs in both LFP and very high resolution BOLD fMRI responses at stimulus condition were around 1 mm, in which stimulus responses in area 3b were stronger and more mediolateral focal than those in area 1. In addition, our results showed that the PSFs of the BOLD response in very high resolution (0.274 × 0.274 mm2) were significantly narrower than those in relatively lower resolution imaging (0.547 × 0.547 mm 2), due to partial volume effects, indicating that data acquisition methods for higher resolution functional images increase the spatial specificity of BOLD fMRI. Finally, Wilcoxon signed-rank test showed that there was no significant difference on PSFs between LFP and very high resolution BOLD fMRI at 9.4 T in the stimulus condition, and the reproducibility and stability of stimulus-evoked activation locations within and across both modalities were robust.
|Advisor:||Gore, John C.|
|Commitee:||Anderson, Adam W., Chen, Li Min, Gore, John C., Rogers, Baxter P., Wilkes, D. Mitchell|
|School Location:||United States -- Tennessee|
|Source:||DAI-B 80/08(E), Dissertation Abstracts International|
|Keywords:||BOLD fMRI, Functional connectivity, Local field potentials, Spatial correspondence|
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