Relative Hemodynamic Timing in Human White Matter

Hemodynamic lag in white matter (WM) remains poorly understood despite its relevance to neurovascular health. We developed Local Propagation Mapping to quantify the spatiotemporal architecture of relative hemodynamic timing within WM. In young adults, WM lag architecture was reliable, aligned with venous anatomy, and reconfigured during working-memory task engagement; the magnitude of macroscopic lag modulation was associated with cognitive performance. Across aging, resting-state WM lag showed tract-specific bidirectional shifts and increased spatial fragmentation, with partial overlap with task-sensitive systems observed in young adults. Static baseline markers did not significantly mediate age-related cognitive differences, suggesting that aging effects may not operate through a simple resting-state pathway. Together, these findings establish relative WM lag as an informative dimension of neurovascular regulation and motivate a baseline-load hypothesis for future studies of cognitive aging.