Mapping small-world properties through development in the human brain: disruption in schizophrenia

Area of Science:

• Neuroscience
• Network Science
• Medical Imaging

Background:

• The human brain exhibits a small-world network topology, crucial for efficient information processing.
• Existing global graph theory measures lack the spatial specificity to pinpoint regional brain abnormalities.
• Disruptions in brain network topology are implicated in various neurological and psychiatric disorders.

Purpose of the Study:

• To develop and validate an ultra-fast methodology for mapping local brain network topology.
• To assess the reliability and variability of novel local measures (local clustering coefficient, local characteristic path length, local small-worldness).
• To investigate age-related changes in brain network topology and identify alterations in schizophrenia.

Main Methods:

• Developed novel ultra-fast algorithms to compute local clustering (lC), local characteristic path length (lL), and local small-worldness (lS).
• Utilized resting-state functional magnetic resonance imaging (rs-fMRI) data to map these local network properties at 3-mm isotropic resolution.
• Validated the methodology using test-retest datasets from healthy children/adolescents and compared findings across age groups and schizophrenia patients.

Main Results:

• The novel measures demonstrated good test-retest reliability (intraclass correlation > 0.5 for lC and lL) and low inter-subject variability (< 29%).
• High local functional connectivity density (lFCD) regions (e.g., posterior parietal cortex) showed high lC and short lL.
• Children/adolescents exhibited distinct network properties compared to adults, with schizophrenia patients showing weaker connectivity in specific regions, suggesting exaggerated pruning.

Conclusions:

• The proposed ultra-fast methodology enables reliable and spatially specific mapping of local brain network topology.
• Age-related changes in brain connectivity are evident, with potential implications for understanding brain maturation.
• Altered local network topology in schizophrenia patients, particularly in thalamus and midbrain, supports theories of thalamic disconnection and exaggerated pruning in the disorder.