Autonomic physiological coupling of the global fMRI signal

The brain is closely attuned to visceral signals from the body's internal environment, as evidenced by the numerous associations between neural, hemodynamic and peripheral physiological signals. Here we show that a major mode of these brain-body cofluctuations can be captured by a single spatiotemporal pattern. Across several independent samples, as well as single-echo and multi-echo functional magnetic resonance imaging (fMRI) data acquisition sequences, we identify widespread cofluctuations in the low-frequency range (0.01-0.1 Hz) between resting-state global fMRI signals, electroencephalogram (EEG) activity, and a host of peripheral autonomic signals spanning cardiovascular, pulmonary, exocrine and smooth muscle systems. The same brain-body cofluctuations observed at rest are elicited by cued deep breathing and intermittent sensory stimuli, as well as spontaneous phasic EEG events during sleep. Furthermore, we show that the spatial structure of global fMRI signals is maintained under experimental suppression of end-tidal carbon dioxide variations, suggesting that respiratory-driven fluctuations in arterial CO₂ accompanying arousal cannot fully explain the origin of these signals in the brain. These findings suggest that the global fMRI signal is a substantial component of the arousal response governed by the autonomic nervous system.