Functional connectivity arises from a slow rhythmic mechanism

Significance Functional connectivity MRI has revolutionized our understanding of brain architecture. Correlated changes in oxygen levels reveal networks of regions. These networks, each linked to particular functions, are conserved across individuals and species. Normal development, learning, and mental disorders are associated with subtle network changes, providing insight into how brains work. Remarkably, the basis of functional connectivity remains unknown. Although some studies have reported data consistent with an oscillatory process, the leading hypothesis involves emergent, arrhythmic dynamics of complex and distributed networks (the “criticality” hypothesis). By using a new electrode-based technique, we show that functional connectivity is not related to criticality, but instead to specific and potentially localizable oscillatory processes. This finding provides a tool to identify the mechanisms underlying functional connectivity. The mechanism underlying temporal correlations among blood oxygen level-dependent signals is unclear. We used oxygen polarography to better characterize oxygen fluctuations and their correlation and to gain insight into the driving mechanism. The power spectrum of local oxygen fluctuations is inversely proportional to frequency raised to a power (1/f) raised to the beta, with an additional positive band-limited component centered at 0.06 Hz. In contrast, the power of the correlated oxygen signal is band limited from ∼0.01 Hz to 0.4 Hz with a peak at 0.06 Hz. These results suggest that there is a band-limited mechanism (or mechanisms) driving interregional oxygen correlation that is distinct from the mechanism(s) driving local (1/f) oxygen fluctuations. Candidates for driving interregional oxygen correlation include rhythmic or pseudo-oscillatory mechanisms.