Sub-Regional Motor–Somatosensory Connectivity and Lifespan Plasticity in Functional Networks

Objectives: To determine how cytoarchitectonically defined subdivisions of the primary motor cortex, somatosensory cortex, and supplementary motor area (SMA) reorganize their integration with large-scale brain networks during healthy aging. This study investigated the lifespan trajectories of functional connectivity within cytoarchitectonically defined subregions of the primary motor cortex, somatosensory cortex, and supplementary motor area (SMA). Methods: We conducted a cross-sectional analysis of resting-state fMRI data from 150 healthy individuals (aged 23–80 years), stratified into young, middle-aged, and older groups. Data were sourced from the Southwest University Adult Lifespan Dataset (SALD) and analyzed between June 2024 and June 2025. Using the Jülich Brain Atlas, we defined seed regions for the M1 (BA4a, BA4p), premotor cortex (6d1–3), PSC (BA1–3), and SMA (pre-SMA, SMA proper). Functional coupling was calculated between these seeds and canonical large-scale networks, including the default mode (DMN), salience, dorsal attention, and frontoparietal systems. Results: Our analysis identified distinct age-dependent connectivity patterns. While all groups maintained robust motor–somatosensory coupling, older adults exhibited a significant loss of network segregation. Specifically, younger adults displayed strong sensorimotor integration with negative DMN coupling, whereas older adults showed widespread, diffuse positive connectivity across the DMN and frontoparietal networks. Middle-aged participants presented a transitional profile with expanded salience network interactions. Conclusion: Aging is associated with a gradual shift from segregated sensorimotor processing to a more dedifferentiated, globally connected architecture. These findings highlight the importance of analyzing specific cytoarchitectonic subdivisions to detect subtle compensatory neuroplasticity mechanisms.