Mapping the Structural Core of Human Cerebral Cortex

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Overview #

This landmark 2008 PLoS Biology study by Hagmann et al. uses diffusion spectrum imaging (DSI) and advanced network analysis to map large-scale structural connectivity across the human cortex. The authors identify a highly interconnected structural core in posterior medial and parietal regions and demonstrate strong correspondence between structural and functional connectivity.

Study Objectives #

• Map cortico-cortical white-matter pathways at high spatial resolution using DSI.

• Construct whole-brain connectivity matrices (998 ROI and 66-region versions).

• Identify structural modules, hubs, and a cortical core using graph-theoretic methods.

• Compare structural connectivity to resting-state functional connectivity from fMRI.

Methods Summary #

Participants & Imaging #

• Five healthy adults underwent high-resolution T1 MRI and DSI scanning.

• 998 cortical ROIs were created using standardized anatomical partitioning.

• Whole-brain tractography estimated inter-regional fiber trajectories.

Network Construction #

• Weighted edges represented fiber density between ROI pairs.

• Supplementary analyses included k-core decomposition, modularity detection, betweenness centrality, and efficiency metrics.

Functional Connectivity #

• Resting-state fMRI was collected from the same participants.

• Structural–functional relationships were evaluated via correlation analyses.

Key Findings #

1. Discovery of a Posterior Medial Structural Core #

The strongest and most central connectivity occurred in:

• Precuneus

• Posterior cingulate cortex

• Isthmus of the cingulate

• Cuneus

• Paracentral lobule
  (all bilateral)

These regions showed:

• Highest degree and strength

• Highest centrality and efficiency

• Persistence in highest-level k-core and s-core networks

2. Modular Network Organization #

Six major cortical modules were identified:

• Bilateral medial modules (posterior cingulate and precuneus centered)

• Contralateral frontal and temporo-parietal modules
  Connector hubs were concentrated along the anterior–posterior medial cortical axis, linking major modules.

3. Structural–Functional Correspondence #

Structural connectivity was significantly predictive of functional connectivity:

• For precuneus/posterior cingulate: r² = 0.53

• Across all regions: r² = 0.62

Functional maps resembled the canonical default mode network, especially in posterior medial regions.

4. Validation & Consistency #

• High intra-participant reliability across scans.

• Consistency with macaque tract-tracing (∼79% concordance).

• Robustness to simulated noise and perturbation of connection matrices.

Interpretation & Implications #

The posterior medial cortex forms a structural backbone integrating information across widespread brain systems. Its overlap with high-metabolic-activity regions and default-mode nodes suggests a central role in:

• Internally oriented cognition

• Integrative processing

• Baseline network architecture

This work represents one of the earliest high-resolution connectome analyses and foundational evidence for a structurally anchored “core” of human brain networks.