Vascular density and distribution in neocortex

Abstract

An amazingly wide range of complex behavior emerges from the cerebral cortex. Much of the information processing that leads to these behaviors is performed in neocortical circuits that span throughout the six layers of the cortex. Maintaining this circuit activity requires substantial quantities of oxygen and energy substrates, which are delivered by the complex yet well-organized and tightly-regulated vascular system. In this review, we provide a detailed characterization of the most relevant anatomical and functional features of the cortical vasculature. This includes a compilation of the available data on laminar variation of vascular density and the topological aspects of the microvascular system. We also review the spatio-temporal dynamics of cortical blood flow regulation and oxygenation, many aspects of which remain poorly understood. Finally, we discuss some of the important implications of vascular density, distribution, oxygenation and blood flow regulation for (laminar) fMRI.

A dynamical model of the laminar BOLD response

“…Occasionally, a distinguishable local fMRI signal maximum (sometimes referred to as 'bump') is observed in the middle depths (Chen et al, 2013;Goense and Logothetis, 2006;Harel et al, 2006;Koopmans et al, 2010), deviating by ~0.2-2% with respect to surrounding depths. Location of this bump may correlate with a higher density of vasculature around middle cortical depths, for example in the primary visual cortex (Lauwers et al, 2008;Schmid et al, 2017a;Weber et al, 2008). Therefore, this observation has led to the suggestion that the bump in the LBR may purely be a result of CBV0 variation across cortical depths (i.e.…”

“…see (Kim and Ogawa, 2012;Ogawa et al, 1993;Uludağ et al, 2009). Although it is known, especially from optical imaging studies, that there are larger CBV changes at the arterial side (in particular for short stimulus durations) (Hillman et al, 2007;Vazquez et al, 2010), the CBV0 of arterial vessels is less than 1/3 compared to that in the capillaries and venous vessels (Gagnon et al, 2015;Schmid et al, 2017a), which together with small amount of dHb in arterial vessels makes the arterial contribution to the fMRI BOLD signal small, and, thus, can be ignored to capture the main effects influencing the LBR. By saying that, our depth-specific model compartments of MV do not represent only venules, but rather a simplified model of both capillaries and venules, being more weighted towards venules.…”

The morphology of the human cerebrovascular system

“…The human brain consumes about 20% of the daily intake of oxygen and glucose, which are supplied to the cortex via arteries, arterioles, and capillaries and drained via the venous system and large sinuses (Schmid, Barrett, Jenny, & Weber, 2017). It is well documented that acute impairment of the cerebral arteries can cause collateral damage (Ossenkoppele et al, 2015) and that venous atrophy may play an important role in the early stages of a number of neurological disorders (Gorelick, Counts, & Nyenhuis, 2016;Kaufman, Milstein, Kaufman, & Milstein, 2013).…”

TDM: a temporal decomposition method for removing venous effects from task-based fMRI

“…Note that the ground-truth expectation is not necessarily a perfectly flat depth profile. This is because vascular density varies, to some degree, across cortical depth (Schmid et al, 2019). Moreover, our 0.8-mm measurements sampled within gray matter are certainly susceptible to partial volume effects from cerebrospinal fluid and white matter.…”