Total cerebral blood volume changes drive macroscopic cerebrospinal fluid flux in humans
Fig 4
Changes in global brain blood volume mediate CSF in- and outflux.
(a) Representative example of the positioning of the most caudal fMRI slices on a sagittal T1-weighted image. The CSF voxels of slice 1 are indicated in orange, slice 2 in pink, and slice 3 in green; the dashed lines are schematic depictions of the respective imaging slices. (b) Average time courses of all transitions from hypercapnia to normocapnia. gGM (black), CSF fMRI signal in slice 1 (orange), slice 2 (pink) and slice 3 (green). The shaded areas represent SEM. Hypercapnia and normocapnia periods are indicated in purple. *p < 0.05, repeated-measures ANOVA (between slices) per subject (n = 17). (c) Average time courses of all transitions from burst to suppression. Global GM (black), CSF fMRI signal in slice 1 (orange), slice 2 (pink) and slice 3 (green). The shaded areas represent SEM. Burst and suppression periods are indicated in light orange and light blue, respectively. *p < 0.05, repeated-measures ANOVA (between slices) per event (n = 21). (d) Mean fMRI-based CSF signal intensities (a.u.) per event of slices 1-3 for steady-state suppression or steady-state burst periods. ** p < 0.005, ***p < 0.001, n.s. not significant. Repeated measures ANOVA with Dunn-Sidak post-hoc comparison. (e) Same as (b) for all transitions from normocapnia to hypercapnia. *p < 0.05, repeated-measures ANOVA (between slices) per subject (n = 17). (f) Same as (C) for all transitions from suppression to burst. ** p < 0.005, ***p < 0.001, repeated-measures ANOVA (between slices) per event (n = 22). (g) Schematic model of the link between neuronal activity (blue), CBV (black), CSF flux (↓ - efflux from the acquisition volume, ↑ - influx into the acquisition volume), fMRI-based CSF signal in slice 1 (orange) and slice 2 (pink). The pie charts symbolize the saturation state of CSF, being either fully saturated (white) or unsaturated (black); the rectangles indicate the signal intensity in the respective slice, which results from the mixing of RF-saturated and fresh CSF. Source data for Fig 4b–4f are available in the source data file (S1 Data).