Electrophysiological lag threads reveal a temporal hierarchy of the human cortex

Abstract

The human brain is spatially organized along functional gradients, but the temporal organization of these gradients remains poorly understood. In EEG and MEG, this question has been difficult to address because volume conduction obscures temporal precedence. Here, we introduce lag-specific orthogonalization, an extension of pairwise orthogonalization that allows us to estimate non-zero-lag amplitude-envelope correlations. Applying this approach to large-scale resting-state MEG, we identify electrophysiological lag threads: reproducible maps of temporal ordering that are most coherent in the alpha and beta bands and organize activity from occipital and sensorimotor regions toward frontal and temporal association cortex. These fast electrophysiological lag threads share subject-specific spatial structure with much slower fMRI lag threads, supporting a neural rather than vascular origin of fMRI lag structure. Finally, we show that cortical lag threads are not fixed anatomical constraints. They covary with age and handedness and are selectively reconfigured during cognitive task performance. Together, these findings reveal a frequency-specific electrophysiological temporal hierarchy of the human cortex that links fast neural dynamics to slower hemodynamic propagation structure.