Inter-individual differences in cerebrovascular reactivity are synchronized within functional networks and tissue layers: evidence from healthy older adults and patients with hypertension

Functional-connectivity mapping has primarily relied resting-state functional MRI (rs-fMRI), and resting-state functional networks (RSNs) have been used widely to represent interactions within brain circuits. However, recent work demonstrated that resting-state functional networks (RSNs) may co-exist with vascular networks. In this work, we clarify the nature of these vascular networks by assessing the spatial covariation structure in breath-holding-based CVR amplitude and lag in a group of healthy older adults. We demonstrate a spatial synchrony in CVR amplitude and lag co-variations across participants confined to RSNs. Such a network structure is not seen when looking at the time-variate BOLD signal response to the breathhold. a network structure is also maintained in older adults with clinical hypertension, demonstrating its robustness against vascular pathologies. CVR amplitude is also found to vary with tissue layer in the grey matter and white matter, being most variable in deep WM and least variable in superficial cortex. Conversely, CVR lag appears to be organized by fibre tracts. This work demonstrates the use of cross-participant covariation patterns in CVR as an informative way of mapping the vascular routes in the GM and WM, and also raises questions about the nature and interpretation of RSNs.