Axial variation of deoxyhemoglobin density as a source of the low-frequency time lag structure in blood oxygenation level-dependent signals

Abstract

Perfusion-related information is reportedly embedded in the low-frequency component of a blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signal. The blood-propagation pattern through the cerebral vascular tree is detected as an interregional lag variation of spontaneous low-frequency oscillations (sLFOs). Mapping of this lag, or phase, has been implicitly treated as a projection of the vascular tree structure onto real space. While accumulating evidence supports the biological significance of this signal component, the physiological basis of the “perfusion lag structure,” a requirement for an integrative resting-state fMRI-signal model, is lacking. In this study, we conducted analyses furthering the hypothesis that the sLFO is not only largely of systemic origin, but also essentially intrinsic to blood, and hence behaves as a virtual tracer. By summing the small fluctuations of instantaneous phase differences between adjacent vascular regions, a velocity response to respiratory challenges was detected. Regarding the relationship to neurovascular coupling, the removal of the whole lag structure, which can be considered as an optimized global-signal regression, resulted in a reduction of inter-individual variance while preserving the fMRI response. Examination of the T2* and S0, or non-BOLD, components of the fMRI signal revealed that the lag structure is deoxyhemoglobin dependent, while paradoxically presenting a signal-magnitude reduction in the venous side of the cerebral vasculature. These findings provide insight into the origin of BOLD sLFOs, suggesting that they are highly intrinsic to the circulating blood.

Timescales of spontaneous fMRI fluctuations relate to structural connectivity in the brain

“…In this view, timescales vary hierarchically (because of variations in cortical microstructure or subcortical inputs), but may not be causally modulated by cortico-cortical structural connections. Regional variations in perfusion, perhaps to support the increased metabolic demands of highly connected hub areas (Liang, Zou, He, & Yang, 2013), could also manifest in corresponding spatial differences in BOLD dynamics (Aso, Urayama, Fukuyama, & Murai, 2019;Di et al, 2012). In the absence of experiments that can causally manipulate structural connectivity, computational modeling will continue to play a crucial role in distinguishing between possible mechanistic explanations of the statistical relationships characterized here, towards an understanding of the general and specific mechanisms through which intrinsic timescales may be shaped.…”

The relationship between attention and avoidance coping in anorexia nervosa: functional magnetic resonance imaging study

“…Finally, a recently proposed denoising method 27,28 was used to cope with contamination from non-neural signal components. This procedure involves tracking regional variations of low-frequency oscillations of systemic origin, using the bandpass-filtered (0.008-0.07 Hz) global signal as an initial seed.…”