Resting states affect spontaneous BOLD oscillations in sensory and paralimbic cortex.

The brain exhibits spontaneous neural activity that depends on the behavioral state of the organism. We asked whether the blood oxygenation level-dependent (BOLD) signal reflects these modulations. BOLD was measured under three steady-state conditions: while subjects kept their eyes closed, kept their eyes open, or while fixating. The BOLD spectral density was calculated across brain voxels and subjects. Visual, sensory-motor, auditory, and retrosplenial cortex showed modulations of the BOLD spectral density by resting state type. All modulated regions showed greater spontaneous BOLD oscillations in the eyes closed than the eyes open or fixation conditions, suggesting that the differences were endogenously driven. Next, we examined the pattern of correlations between regions whose ongoing BOLD signal was modulated by resting state type. Regional neuronal correlations were estimated using an analytic procedure from the comparison of BOLD-BOLD covariances in the fixation and eyes closed conditions. Most regions were highly correlated with one another, with the exception of the primary visual cortices, which showed low correlations with the other regions. In conclusion, changes in resting state were associated with synchronous modulations of spontaneous BOLD oscillations in cortical sensory areas driven by two spatially overlapping, but temporally uncorrelated signals.