Functional Integration of the Subregions of the Primary Motor Cortex: The Impact of Handedness and Hemispheric Lateralization.

Objective: Cytoarchitectonic mapping has revealed distinct subregions within Broadmann area 4 (BA 4) - BA 4a and BA 4p - with varying functional roles across tasks. We investigate their functional connectivity using resting-state functional magnetic resonance imaging (rsfMRI) to explore bilateral differences and the impact of handedness on connectivity within major brain networks.

Methods: This retrospective study involved 54 left- and right-handed subjects. We employed regions-to-regions-network rsfMRI analysis to examine the Cytoarchitectonic mapping of BA 4a and BA 4p functional connectivity with eight major brain networks.

Results: Our findings reveal differential connectivity patterns in both right-handed and left-handed subjects: Both right-handed subjects' BA 4a and BA 4p subregions exhibit connections to sensorimotor, dorsal attention, frontoparietal, and anterior cerebellar networks. Notably, BA 4a shows unique connectivity to the posterior cerebellum, lateral visual networks, and select salience regions. Similar connectivity patterns are observed in left-handed subjects, with BA 4a linked to sensorimotor, dorsal attention, frontoparietal, and anterior cerebellar networks. However, BA 4a in left-handed subjects shows distinct connectivity only to the posterior cerebellum. In both groups, the right portion of BA 4 demonstrates heightened connectivity compared to the left portion within each subregion.

Conclusion: Our study uncovers complex patterns of functional connectivity within BA 4a and BA 4p, influenced by handedness. These findings emphasize the importance of considering hemisphere-specific and handedness-related factors in functional connectivity analyses, with potential implications for understanding brain organization in health and neurodegenerative diseases.