Synchronized delta oscillations correlate with the resting-state functional MRI signal - PubMed (original) (raw)

Synchronized delta oscillations correlate with the resting-state functional MRI signal

Hanbing Lu et al. Proc Natl Acad Sci U S A. 2007.

Abstract

Synchronized low-frequency spontaneous fluctuations of the functional MRI (fMRI) signal have recently been applied to investigate large-scale neuronal networks of the brain in the absence of specific task instructions. However, the underlying neural mechanisms of these fluctuations remain largely unknown. To this end, electrophysiological recordings and resting-state fMRI measurements were conducted in alpha-chloralose-anesthetized rats. Using a seed-voxel analysis strategy, region-specific, anesthetic dose-dependent fMRI resting-state functional connectivity was detected in bilateral primary somatosensory cortex (S1FL) of the resting brain. Cortical electroencephalographic signals were also recorded from bilateral S1FL; a visual cortex locus served as a control site. Results demonstrate that, unlike the evoked fMRI response that correlates with power changes in the gamma bands, the resting-state fMRI signal correlates with the power coherence in low-frequency bands, particularly the delta band. These data indicate that hemodynamic fMRI signal differentially registers specific electrical oscillatory frequency band activity, suggesting that fMRI may be able to distinguish the ongoing from the evoked activity of the brain.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

Effect of α-chloralose dose on resting-state functional connectivity in rat primary somatosensory cortex (S1FL). (A) 3D representation of color-coded group _t_-statistical maps thresholded at P < 0.025 (n = 6). The seed voxels were chosen from the left S1FL. Functional connectivity within the left hemisphere persisted during all three doses of α-chloralose, whereas the functional connectivity within the right hemisphere decreased as the anesthesia dose increased, suggesting that interhemispheric synchrony of the spontaneous fluctuations was significantly modulated by α-chloralose. (B and C) Low-pass-filtered resting-state fMRI time courses (with mean removed) at α-chloralose dose of 30 and 100 mg/kg from one animal (cutoff frequency = 0.1 Hz). Time courses from bilateral S1FL appear visually to be more synchronized at low anesthesia levels. CC values in bilateral S1FL at three anesthetic doses are shown in D. CC values in the right hemisphere were significantly reduced compared with those in the left hemisphere at α-chloralose doses of 70 and 100 mg/kg. There was no significant difference at 30 mg/kg. *, P < 0.05.

Fig. 2.

Fig. 2.

Semilog plot of the distribution of EEG power across frequency bands in α-chloralose-anesthetized rats. Low frequencies, in particular the δ band, dominate the power spectra. There were no significant differences in the power distributions between the three levels of anesthesia (n = 8 rats).

Fig. 3.

Fig. 3.

Power time courses showing variations of the EEG signal from the bilateral S1FL and the visual cortex from one animal. Dotted vertical lines indicate covariations of signals among the three recording sites. δ band power time courses from bilateral S1FL (LF, RF) exhibited more synchronized fluctuations than from right visual cortex (RV), and the synchrony was more pronounced at 30 mg/kg than at 100 mg/kg α-chloralose. Only δ and γ band power time courses are shown for graphic clarity.

Fig. 4.

Fig. 4.

Statistical comparisons of power correlations between electrode pairs and anesthesia levels. For the δ band, at 30 mg/kg α-chloralose, the power correlation between the left and right somatosensory cortical electrodes was significantly higher than at the two higher doses (Wilcoxon signed-ranks test, P < 0.04). No significant dose differences were found for either the LF or the RF electrode and the RV. Among electrode pairs, the differences were most pronounced at 30 mg/kg, where the power correlations between LF-RF electrodes were greater than those between LF-RV and between RF-RV pairs (Wilcoxon signed-ranks test, P = 0.01 and 0.02, respectively). *, P < 0.05. (Abbreviations as in Fig. 3.)

Fig. 5.

Fig. 5.

Anesthetic dose modulations of the δ band EEG power and resting-state fMRI signals in bilateral S1FL. Note the similar patterns of anesthetic dose modulation on these two signal types. C.C. is the cross-correlation coefficient of the EEG power time course and fMRI signal within bilateral S1FL.

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