Tracking brain arousal fluctuations with fMRI

Significance Changes in vigilance and arousal levels can interfere with the study of brain function with functional MRI (fMRI). However, the difficulty of tracking and modeling arousal state during fMRI typically precludes the assessment of arousal-dependent influences on fMRI measurements. Here, we present evidence that continuous variations in arousal level may be monitored from fMRI data alone and validate this approach with a combination of fMRI, intracortical electrophysiology, and a behavioral measure of arousal. We describe a spatial pattern whose time-varying expression in the fMRI data is found to track both electrophysiological and behavioral arousal fluctuations. These findings have implications for increasing the sensitivity of fMRI as a cognitive and clinical biomarker. Changes in brain activity accompanying shifts in vigilance and arousal can interfere with the study of other intrinsic and task-evoked characteristics of brain function. However, the difficulty of tracking and modeling the arousal state during functional MRI (fMRI) typically precludes the assessment of arousal-dependent influences on fMRI signals. Here we combine fMRI, electrophysiology, and the monitoring of eyelid behavior to demonstrate an approach for tracking continuous variations in arousal level from fMRI data. We first characterize the spatial distribution of fMRI signal fluctuations that track a measure of behavioral arousal; taking this pattern as a template, and using the local field potential as a simultaneous and independent measure of cortical activity, we observe that the time-varying expression level of this template in fMRI data provides a close approximation of electrophysiological arousal. We discuss the potential benefit of these findings for increasing the sensitivity of fMRI as a cognitive and clinical biomarker.