title: Broadband local field potentials correlate with spontaneous fluctuations in functional magnetic resonance imaging signals in the rat somatosensory cortex under isoflurane anesthesia.
abstract: Resting-state functional magnetic resonance imaging (fMRI) is widely used for exploring spontaneous brain activity and large-scale networks; however, the neural processes underlying the observed resting-state fMRI signals are not fully understood. To investigate the neural correlates of spontaneous low-frequency fMRI fluctuations and functional connectivity, we developed a rat model of simultaneous fMRI and multiple-site intracortical neural recordings. This allowed a direct comparison to be made between the spontaneous signals and interhemispheric connectivity measured with the two modalities. Results show that low-frequency blood oxygen level-dependent (BOLD) fluctuations (<0.1 Hz) correlate significantly with slow power modulations (<0.1 Hz) of local field potentials (LFPs) in a broad frequency range (1-100 Hz) under isoflurane anesthesia (1%-1.8%). Peak correlation occurred between neural and hemodynamic activity when the BOLD signal was delayed by ~4 sec relative to the LFP signal. The spatial location and extent of correlation was highly reproducible across studies, with the maximum correlation localized to a small area surrounding the site of microelectrode recording and to the homologous area in the contralateral hemisphere for most rats. Interhemispheric connectivity was calculated using BOLD correlation and band-limited LFP (1-4, 4-8, 8-14, 14-25, 25-40, and 40-100 Hz) coherence. Significant coherence was observed for the slow power changes of all LFP frequency bands as well as in the low-frequency BOLD data. A preliminary investigation of the effect of anesthesia on interhemispheric connectivity indicates that coherence in the high-frequency LFP bands declines with increasing doses of isoflurane, whereas coherence in the low-frequency LFP bands and the BOLD signal increases. These findings suggest that resting-state fMRI signals might be a reflection of broadband LFP power modulation, at least in isoflurane-anesthetized rats.
authors.affiliation: Department of Biomedical Engineering, Emory University/Georgia Institute of Technology, Atlanta, Georgia 30322, USA.
authors.forename: Wen-Ju
authors.initials: WJ
authors.lastname: Pan
authors.forename: Garth
authors.initials: G
authors.lastname: Thompson
authors.forename: Matthew
authors.initials: M
authors.lastname: Magnuson
authors.forename: Waqas
authors.initials: W
authors.lastname: Majeed
authors.forename: Dieter
authors.initials: D
authors.lastname: Jaeger
authors.forename: Shella
authors.initials: S
authors.lastname: Keilholz
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000769:Anesthesia, Inhalation / Q000379:methods*; D000818:Animals; D004567:Electrodes, Implanted; D007530:Isoflurane / Q000494:pharmacology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013003:Somatosensory Cortex / Q000187:drug effects* / Q000502:physiology*
chemical_list: D007530:Isoflurane