Sub-Networks of the Brain R2 Structural Connectome Integrity Matrix (SCIM) and Older Adult Cognitive and Motor Functioning.

Factor analysis of the R2 structural connectome integrity matrix revealed four distinct Sub-Networks (SN) with characteristic regional node compositions.

• SN-1 involved most frontal nodes, all parietal nodes, and key subcortical (basal ganglia) structures.
• SN-2 involved most albeit slightly different frontal nodes than SN-1, nearly all temporal and key subcortical (limbic) nodes.
• SN-3 was primarily characterized by edges involving select parietal and temporal and all occipital nodes.
• SN-4 was confined to cerebellum, basal ganglia, and limbic nodes.
• The sample consisted of 1239 participants with mean age approximately 79 ± 7 years.

Lower R2 in SN-1, SN-2, and SN-4 was associated with lower baseline global cognition.

• Associations were identified using a linear mixed-effects regression model containing weighted composite scores representing each Sub-Network.
• Models adjusted for relevant confounders.
• Three of the four Sub-Networks (SN-1, SN-2, SN-4) showed associations with baseline global cognitive performance.
• SN-3 was not associated with baseline global cognition.

Lower R2 in SN-2 and SN-3 was associated with faster declines in global cognition over time.

• Longitudinal cognitive decline was assessed using linear mixed-effects regression models.
• SN-2 and SN-3 were specifically implicated in cognitive decline trajectories.
• SN-1 and SN-4 were not associated with rate of change in global cognition over time.
• Sub-Networks were also differentially associated with domain-specific cognitive functions at baseline and over time.

Nearly all Sub-Networks were negatively associated with global motor function, dexterity, and gait speed at baseline.

• Global motor function, dexterity, and gait speed were the motor outcomes examined.
• The association with baseline motor functioning was present across almost all four Sub-Networks.
• This suggests broad structural connectome integrity relevance to motor functioning at a single time point.

Only SN-1 and SN-4 were associated with change in motor functioning over time, specifically gait speed.

• Longitudinal motor associations were more selective than baseline motor associations.
• SN-2 and SN-3 were not associated with change in motor functioning over time.
• The specific motor domain associated with longitudinal change was gait speed.
• SN-1 involves frontal, parietal, and basal ganglia nodes; SN-4 involves cerebellum, basal ganglia, and limbic nodes.

The study used transverse relaxation rates (R2) derived from white matter connections defined via a structural connectivity-based atlas to form the structural connectome integrity matrix.

• R2 is a measure of transverse relaxation rate applied to white matter connections.
• A structural connectivity-based atlas was used to define white matter connections.
• The resulting matrix was termed the Structural Connectome Integrity Matrix (SCIM).
• The sample included 1239 older adult participants with mean age approximately 79 ± 7 years.
• This approach was applied to neuroimaging data from what appears to be a large cohort study of aging.