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INNOVATIVE METHODOLOGY

Methods for Determining Frequency- and Region-Dependent Relationships Between Estimated LFPs and BOLD Responses in Humans

¹Radiology Service and ⁴Neuropsychology and Neurorehabilitation Service, University Hospital Center and University of Lausanne, Lausanne, Switzerland; ²Signal Processing Institute, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; ³Center for Biomedical Imaging of Lausanne and Geneva, Lausanne, Switzerland; ⁵Functional Brain Mapping Laboratory and ⁶Electrical Neuroimaging Group, Department of Neurology, University Hospital, Geneva, Switzerland; and ⁷Neurodynamics Laboratory, Department of Psychiatry and Clinic Psychobiology, University of Barcelona, Catalonia, Spain

Submitted 6 March 2008; accepted in final form 9 September 2008

The relationship between electrophysiological and functional magnetic resonance imaging (fMRI) signals remains poorly understood. To date, studies have required invasive methods and have been limited to single functional regions and thus cannot account for possible variations across brain regions. Here we present a method that uses fMRI data and singe-trial electroencephalography (EEG) analyses to assess the spatial and spectral dependencies between the blood-oxygenation-level-dependent (BOLD) responses and the noninvasively estimated local field potentials (eLFPs) over a wide range of frequencies (0–256 Hz) throughout the entire brain volume. This method was applied in a study where human subjects completed separate fMRI and EEG sessions while performing a passive visual task. Intracranial LFPs were estimated from the scalp-recorded data using the ELECTRA source model. We compared statistical images from BOLD signals with statistical images of each frequency of the eLFPs. In agreement with previous studies in animals, we found a significant correspondence between LFP and BOLD statistical images in the gamma band (44–78 Hz) within primary visual cortices. In addition, significant correspondence was observed at low frequencies (<14 Hz) and also at very high frequencies (>100 Hz). Effects within extrastriate visual areas showed a different correspondence that not only included those frequency ranges observed in primary cortices but also additional frequencies. Results therefore suggest that the relationship between electrophysiological and hemodynamic signals thus might vary both as a function of frequency and anatomical region.