Inward versus reward: white matter pathways in extraversion.

The trait of extraversion is one of the longest-standing domains that captures the social dimension of personality and can potentially explain the covariation of a wide variety of behaviors. To date, there is a growing recognition that human behavior should be specified not only through the psychological mechanisms underlying each trait but also through their underlying neurobehavioral systems. While imaging studies have revealed important initial insights into the structural and functional neural correlates of extraversion, current knowledge about the relationships between extraversion and brain structures is still rather limited, especially with regard to the relationship between extraversion and white matter (WM). In this study, we aimed to investigate WM microstructure in extraversion in greater depth. Thirty-five healthy volunteers (21 women; mean age 35) underwent magnetic resonance imaging, as a part of a larger project aimed at investigating the longitudinal effect of motor training. WM integrity was assessed using the diffusion tensor imaging technique combining multiple diffusion tensor measures. Extraversion was assessed by the Eysenck Personality Questionnaire-Revised. Voxelwise correlation analyses between fractional anisotropy, axial diffusivities, and radial diffusivities maps and extraversion score showed decreased connectivity in the right inferior fronto-occipital fasciculus and forceps major among individuals who had high extraversion ratings. In conclusion, individual differences in extraversion may reflect differential organization of the WM tracts connecting frontal cortex, temporal, and occipital areas, which are related to socioemotional and control functions.

Multimodal assessment of hemispheric lateralization for language and its relevance for behavior.

Although different MRI-based techniques have been proposed to assess the hemispheric lateralization for language (HLL), the agreement across methods, and its relationship with language abilities, are still a matter of debate. In the present study we obtained measures of HLL using both task-evoked activity during the execution of three different protocols and task-free methods of functional [resting state functional connectivity (rs-FC)] and anatomical [diffusion tensor imaging (DTI) tractography] connectivity. Regional analyses focusing on the perisylvian language network were conducted to assess the consistency of HLL across techniques. In addition, following a multimodal approach, we identified macro-factors of lateralization and examined their relationship with language performance. Our findings indicate the existence of a negative relationship between the structural asymmetry of the direct segment of the arcuate fasciculus (AF) and the inter-hemispheric rs-FC of key nodes of the perisylvian network. Instead, despite all the language tasks exhibited a leftward pattern of asymmetry, measures of HLL derived from task-evoked activity did not show a direct relationship with those obtained with the two task-free methods. Furthermore, a robust brain-behavioral relationship was observed only with a specific macro-factor that combined HLL measures derived from all MRI techniques. In particular, general language performance was positively related to more symmetrical structural organization, stronger inter-hemispheric communication at rest but more lateralized activation of Wernicke's territory during production tasks. Our findings, while not supporting the existence of a direct relationship between indices of hemispheric lateralization for language derived from different MRI techniques, indicate that general language performance can be indexed using combined MRI measures. The same approach might prove successful for likewise complex human behaviours.