Representation of arousal states by temporal dynamics of brain-wide traveling wave patterns in resting-state fMRI

As traveling waves mediate neural information processing that depends on arousal states, we hypothesized that traveling waves would represent arousal states. To investigate this, we aimed to analyze brain-wide patterns of traveling waves during resting states using functional magnetic resonance imaging (rsfMRI). Specifically we focused on the temporal dynamics of the brain-wide patterns of rsfMRI traveling waves in association with arousal states. Using a publicly available dataset (N = 27), we extracted infra-slow (0.01-0.1 Hz) activity from blood oxygen level dependent (BOLD) signals. From infra-slow activity, we measured traveling waves via local phase gradient (LPG). Then, we clustered brain-wide LPGs through the k-means algorithm to extract brain-wide patterns of traveling waves, where each cluster represented each pattern. The optimal number of clusters was found to be 2. We analyzed the temporal dynamics of these clusters in relation to arousal states. During low-arousal states, brain-wide patterns of traveling waves featured in Cluster 1 appeared more often. During high-arousal states, those in Cluster 2 did so and lasted longer. As arousal increased, cluster dwell times shortened and transitions between clusters became more frequent, with the opposite pattern observed as arousal decreased. These findings suggest that brain-wide patterns of rsfMRI traveling waves reflect arousal states through their temporal dynamics, forming a syntax underlying arousal.