Abstract
The brain structural and functional basis of lateralization in handedness is largely unclear. This study aimed to explore this issue by using voxel-mirrored homotopic connectivity (VMHC) measured by resting-state functional MRI (R-fMRI) and gray matter asymmetry index (AI) by high-resolution anatomical images. A total of 50 healthy subjects were included, among them were 13 left-handers, 24 right-handers, and 13 mixed-handers. Structural and R-fMRI data of all subjects were collected. There were significant differences in VMHC among the three groups in lateral temporal-occipital, orbitofrontal, and primary hand motor regions. Meanwhile, there were significant differences in AI that existed in medial prefrontal, superior frontal, and superior temporal regions. Besides, the correlation analysis showed that the closer the handedness score to the extreme of the left-handedness (LH), the stronger the interhemispheric functional connectivity, as well as more leftward gray matter. In general, left/mixed-handedness (MH) showed stronger functional homotopy in the transmodal association regions that depend on the integrity of the corpus callosum, but more variable in primary sensorimotor cortices. Furthermore, the group differences in VMHC largely align with that in AI. We located the specific regions for LH/MH from the perspective of structural specification and functional integration, suggesting the plasticity of hand movement and different patterns of emotional processing.
Highlights
Between-group differences in voxel-mirrored homotopic connectivity (VMHC) are shown in Figure 1 and Table 2
We found that the LH showed a decrease in rightward on the STG compared with RH, which suggested that LH could be related to the enhancement of language lateralization in the right superior temporal gyrus
We found the differences of asymmetry index (AI) in the medial prefrontal cortex and the superior frontal gyrus (SFG), which indicated that different handedness had different or the same but different degrees of hemispheric dominance in emotional expression and self-awareness
Summary
Human brain behaviors exhibit significant lateralization (Ocklenburg et al, 2014), including language (Ocklenburg et al, 2013; Yazbek et al, 2020), visuospatial (Vogel et al, 2003; Tokgoz et al, 2020), memory (Babiloni et al, 2006; Zhou et al, 2020), attention (Duecker et al, 2013), and emotional processing (Lindell, 2013). The brain basis of these lateralized behaviors is supposed to be associated with prominent structural asymmetries, including the lateral fissure (Rubens et al, 1976; Toga and Thompson, 2003; Essen, 2005) and the supratemporal sulcus (Shapleske et al, 1999; Hirayasu et al, 2000); the structure and the function of lateralization behavior, such as the handedness, is still an open question. Previous research (Willems et al, 2014) suggests that left-handers tend to weaken brain lateralization, as compared to right-handers. The evidence in these documents suggests that left-handers may have distinct interhemispheric interaction patterns and macroscale organization, both structurally and functionally
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