Whole-brain, gray and white matter time-locked functional signal changes with simple tasks and model-free analysis

Recent studies have revealed that blood oxygenation-level dependent (BOLD) signal changes correlate with task timings throughout a majority of the cortex, challenging the idea of sparse and localized brain functions, and highlighting the pervasiveness of potential false negative fMRI findings. However, these studies have focused on gray matter only. We extend the analysis to white matter and find widespread BOLD signal changes in both white and gray matter, challenging the idea of sparse functional localization, but also the prevailing wisdom of treating white matter BOLD signals as artefacts to be removed.