A Parsimonious Description of Global Functional Brain Organization in Three Spatiotemporal Patterns

Summary

Resting-state functional MRI has yielded many, seemingly disparate insights into large-scale organization of the human brain. Representations of the brain’s large-scale organization can be divided into two broad categories - zero-lag representations of functional connectivity structure and time-lag representations of traveling wave or propagation structure. Here we sought to unify multiple observed phenomena in these two categories by applying concepts from the study of standing (zero-lag) and traveling (time-lag) waves. Using simulated data, we first described the behavior of zero-lag and time-lag analyses applied to spatiotemporal patterns with varying degrees of standing and traveling wave patterns. We then identified three low-frequency spatiotemporal patterns in empirical resting-state fMRI signals, composed of a mixture of standing and traveling wave dynamics, that describe both the zero-lag and time-lag structure of these signals. We showed that a wide range of previously observed empirical phenomena, including functional connectivity gradients, the task-positive/task-negative pattern, the global signal, time-lag propagation patterns, the quasiperiodic pattern, and the functional connectome network structure are manifestations of these three spatiotemporal patterns. These patterns account for much of the global spatial structure that underlies functional connectivity analyses, and therefore impact how we interpret everything derived from resting-state fMRI data from functional networks to graphs.