Human social activities are realized by a synergy of neuronal activity over various regions of the brain, which is supported by their connectivity. In the present study, we examined associations between social activities, represented by work hours, and brain connectivity as quantified using diffusion tensor imaging (DTI). In 483 healthy participants, DTI analysis was performed using 3 T magnetic resonance imaging, and work hours were calculated, considering hours of paid employment (the "Work for Pay" category), hours of housework (the "Work at Home" category), and hours of school-related study (the "Student" category). The correlations between each class of work time and DTI indices were analyzed. The mean diffusivity (MD) values of the anterior limb of the internal capsule (ALIC) and the superior fronto-occipital fasciculus (SFO) were negatively correlated with total work hours (ALIC: r = -0.192, p = 2.3 × 10-5; SFO: r = -0.161, p = 3.8 × 10-4). We also found that the MD values of the ALIC and the SFO were correlated with work hours in the Work for Pay category (ALIC: r = -0.211, p = 3.2 × 10-6; SFO: r = -0.163, p = 3.4 × 10-4) but not with those in the Work at Home category or the Student category. These results suggest that social activity is associated with the white matter microstructure of the ALIC and the SFO. The main difference between "Work for Pay" and the other two social activities appears to be the type of motivation-for example, external versus internal. Therefore, the white matter microstructure of the ALIC and SFO may be related to externally motivated social activities.
Keywords: Anterior limb of internal capsule; Diffusion tensor imaging (DTI); Mean diffusivity (MD); Superior fronto-occipital fasciculus; White matter; Work hours.
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