Abstract
.Modulation of brain state, e.g., by anesthesia, alters the correlation structure of spontaneous activity, especially in the delta band. This effect has largely been attributed to the slow oscillation that is characteristic of anesthesia and nonrapid eye movement (NREM) sleep. However, the effect of the slow oscillation on correlation structures and the spectral content of spontaneous activity across brain states (including NREM) has not been comprehensively examined. Further, discrepancies between activity dynamics observed with hemoglobin versus calcium (GCaMP6) imaging have not been reconciled. Lastly, whether the slow oscillation replaces functional connectivity (FC) patterns typical of the alert state, or superimposes on them, remains unclear. Here, we use wide-field calcium imaging to study spontaneous cortical activity in awake, anesthetized, and naturally sleeping mice. We find modest brain state-dependent changes in infraslow correlations but larger changes in GCaMP6 delta correlations. Principal component analysis of GCaMP6 sleep/anesthesia data in the delta band revealed that the slow oscillation is largely confined to the first three components. Removal of these components revealed a correlation structure strikingly similar to that observed during wake. These results indicate that, during NREM sleep/anesthesia, the slow oscillation superimposes onto a canonical FC architecture.
Highlights
Correlation analysis of spontaneous brain activity has been increasingly used in systems neuroscience.[1,2,3,4] This methodology provides a powerful approach for mapping various cognitive processes as well as understanding specific clinical populations.[5]
To examine the influence of brain state on correlation structures, electroencephalography/ electromyography (EEG/EMG) recordings were simultaneously collected for scoring specific time epochs as wake, nonrapid eye movement (NREM) sleep, anesthesia, or movement artifact [Fig. 1(a)]
EEG and EMG were scored in 10-s epochs by standard criteria[36] as either wake, NREM sleep, anesthesia, or artifact and visualized using hypnograms [Fig. 1(c); see Supplementary Figure S1 for quantification of time spent in each brain state]
Summary
Correlation analysis of spontaneous brain activity has been increasingly used in systems neuroscience.[1,2,3,4] This methodology provides a powerful approach for mapping various cognitive processes as well as understanding specific clinical populations.[5]. Wide-field optical imaging modalities, such as optical intrinsic signal (OIS) imaging, allow for the same FC analysis to be performed in mice.[10] More recently, FC patterns extracted from wide-field optical imaging have been identified within neural calcium dynamics in mice that express genetically encoded calcium indicators (GECIs).[11,12,13] These fluorophores have extended the temporal frequency range in which FC can be studied and provide detailed maps of FC across the whole cortex.[14] Another advantage of fluorophore imaging is that fluorescence is dependent on cell-specific calcium flux, providing a more direct read-out of neural activity that is independent of neurovascular coupling. The delta band “slow oscillation” that is a hallmark of nonrapid eye movement (NREM) sleep appears to be a distinct physiological phenomenon from resting state FC, and it will be important to understand the potential confounding effects of these slow oscillations on FC analysis
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