Mapping the Structural Core of Human Cerebral Cortex

Structurally segregated and functionally specialized regions of the human cerebral cortex are interconnected by a dense network of cortico-cortical axonal pathways. By using diffusion spectrum imaging, we noninvasively mapped these pathways within and across cortical hemispheres in individual human participants. An analysis of the resulting large-scale structural brain networks reveals a structural core within posterior medial and parietal cerebral cortex, as well as several distinct temporal and frontal modules. Brain regions within the structural core share high degree, strength, and betweenness centrality, and they constitute connector hubs that link all major structural modules. The structural core contains brain regions that form the posterior components of the human default network. Looking both within and outside of core regions, we observed a substantial correspondence between structural connectivity and resting-state functional connectivity measured in the same participants. The spatial and topological centrality of the core within cortex suggests an important role in functional integration

Cerebral blood volume and flow, as derived from the IVIM parameters.

<p>Cerebral blood volume CBV [ml/100ml] and cerebral blood flow CBF [ml/100ml/min], as calculated from the corresponding IVIM perfusion parameters from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117706#pone.0117706.t001" target="_blank">Table 1</a>. Percentage variations and p-values stay the same and are not reproduced.</p><p>Cerebral blood volume and flow, as derived from the IVIM parameters.</p

Fit Simulation.

<p>(<b>A</b>) Simulation fitting result (mean (full line) ± standard deviation (area)) compared to ideal result (dashed line) as a function of SNR, for the perfusion fraction f, the pseudo-diffusion coefficient D*, the flow-related coefficient fD*, and the diffusion coefficient D. For better visualization, the plot of D was separated from the rest of the plot. The fitting results converge toward the ideal value between SNR 50 and 100. (<b>B-C</b>) Simulation results of the fitting method (full line) compared to ideal result (dashed line) as a function of the variables f and D*, including experimental noise. Interestingly, in all three simulations, the standard deviation of the fitting of fD* is generally smaller than the one of f and D*.</p

Quantitative measurement of IVIM parameters in the visual and the non-visual brain.

<p>The IVIM perfusion parameters D* [10^-3 mm²·s^-1], fD* [10^-3 mm²·s^-1] and f [%], as well as the diffusion coefficient D [10^-3 mm²·s^-1], obtained in the white and gray matter of a region of interest in the visual cortex and in the rest of a full axial slice excluding the occipital lobe.</p><p>Quantitative measurement of IVIM parameters in the visual and the non-visual brain.</p

IVIM flow maps.

<p>(<b>A</b>) In-plane high-resolution (1.2x1.2 mm) maps of the blood flow related IVIM parameter fD*, in 5 consecutive measurements in a single volunteer. An increase in perfusion in the activated primary visual cortex is observed during stimulation compared to baseline. Scale of the colorbar: mm²·s^-1. (<b>B</b>) Corresponding IVIM subtraction maps and the corresponding BOLD statistical t-map. Scale of the colorbar: 10^-3 mm²·s^-1 (IVIM) and t-value (BOLD).</p

IVIM flow subtraction maps.

<p>Maps of the difference in blood flow related IVIM parameter fD*, in all volunteers (except the one already shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117706#pone.0117706.g002" target="_blank">Fig. 2</a>), as obtained by subtracting the averaged flow maps obtained under baseline to the averaged maps obtained under visual stimulation. Scale of the colorbar: 10^-3 mm²·s^-1. The corresponding BOLD statistical t-map is given below each IVIM subtraction map.</p

Bland Altman comparison, average μ ± standard deviation σ, bias and p-values, between non-gated (n.g.) and respectively systolic and diastolic IVIM measurements (n = 11).

<p>Bland Altman comparison, average μ ± standard deviation σ, bias and p-values, between non-gated (n.g.) and respectively systolic and diastolic IVIM measurements (n = 11).</p

Phase contrast flow measurement (blue) and blood flow related parameter, fD*, as function of the cardiac cycle for five subjects (a–e).

<p>(<b>f</b>) Group average (errorbars give ± standard deviation) of fD* overlaid on a group average of flow measurements in the ACA (shading gives ± standard deviation).</p

Olivary-cerebellar cortex connections and olivary-dentate-olivary loop.

<p>A) Sagittal tractography view, in a DWI image background on the left, showing the connections between (i) the Inferior olivary nucleus (green region of interest -ROI) and the cerebellar cortex (light bright green fiber trajectories) and (ii) the Inferior olivary nucleus and the Dentate nucleus (dark green fiber trajectories). The ROI in the Inferior olive is shown in the sagittal, coronal, and axial planes in the images at bottom (from left to right). B), C) and D) Axial tractography view, in a DWI background, showing: B) the connections between (i) the Inferior olivary nucleus (green ROI) and the dentate nucleus (DN) through Dentate nucleus climbing fibers (DNCF) and (ii) the connections between the inferior olivary nucleus (green ROI) and the cortex through cortical climbing fibers (CCF); C) the intersection between the CCF and parallel fibers (PF) from the granule cell axons. D) PF in the cerebellar cortex. E) and F) Tractography magnification of an axial view of the cerebellar cortex, in DWI background. PF and on the left, PF intersecting CCF. G), H), I) 3D tractography view, in a DWI background, showing: G) some PF traversing the cerebellar cortex. H) PF crossing CF that are oriented perpendicular to them. I) Higher magnification of H).</p

Dentate nucleus connections.

<p>A) Sagittal view and B) sagittal and axial 3D view of the Dentate nucleus (DN - see yellow ROI) in a b0 background image. We show: (i) a subset of connections between DN and the cerebellar cortex (lateral hemisphere) and (ii) fibers identified by the ROI in the DN travelling in the MCP and the SCP. C) 3D localization of the Dentate Nucleus (yellow ROI) in a b0 background image in sagittal, coronal, and axial views (from left to right).</p