Brain Structure And Function In Left- And Right-handedness: A Multi-modal MRI Study

Objective:Handedness is also known as "dominant hand",that is preferred to be used in daily life.As we all know,there are some differences in behavioral characteristics,brain structure and brain function between left-(LH)and right-handedness(RH)adults.However,whether there are correlations between changes in macro-and micro-structure of brain white matter(WM),changes in brain function and brain structure,and how these changes relate to each other are still unclear.In the study,multi-modal magnetic resonance imaging(MRI)data analyses were used to compare differences in brain GM volume,macro-and micro-structure of brain WM,and brain functional activity between LH and RH adults,and correlations between these measures were also examined.Aims of the present study are to investigate the neural associations between human brain structure,brain function and behavioral habits or characteristics,providing experimental basis to clarify the neural mechanisms of handedness-related differences.Materials and methods:Fifty-five students from Tianjin Medical University were recruited for the study.Twenty-three were LH healthy subjects(13 males,age: 19-29 years,handedness scores:-66.52±2.09),and thirty-two were RH healthy subjects(16 males,age: 22-30 years,handedness scores: 95.31±1.77).Structural magnetic resonance imaging(s MRI),diffusion tensor imaging(DTI)and resting-state functional magnetic resonance imaging(f MRI)were performed on all subjects.The study consists of three parts.Part I: GM and WM volume and their brain asymmetries(measured using voxel-based morphometry),volumetric deformation(measured using deformation-based morphometry),fractional anisotropy(FA)and mean diffusivity(MD)were compared voxel-by-voxel between LH and RH groups.Then,deterministic fiber tracking was used to investigate group differences of parameter values in fiber bundle via the regions of interest(ROIs)with significant groups differences in WM volume,FA or MD,respectively.Part II: ALFF,Re Ho and functional connectivity density(FCD)were compared voxel-by-voxel between the two groups.Then,the same brain regions with group differences by various analytical methods were used as ROIs,ROI-based functional connectivity analysis was used to investigate the group differences in functional connectivity between ROI and whole brain voxels.Part III: Pearson correlation analysis was used to examine correlations between macro-and micro-structural changes in brain WM,between volume and shape changes in brain GM and WM,and between GM volume and brain functional changes both in LH and RH groups.Results:Compared with RH group,the LH group showed increased ALFF,short-and long-range FCD in the left precuneus(pre Cun),increased ALFF and Re Ho in the right anterior cingulate gyrus(ACG),left inferior parietal gyrus(IPG)and superior parietal gyrus(SPG)and positive correlations between ALFF and Re Ho both in the right ACG and left IPG.And there was increased brain GM volume in the left IPG the LH group.Although the group differences were detected both in brain function and GM volume,while there was no correlation observed between the changes in brain function and GM volume in the left IPG.The LH group also showed decreased brain WM volume in bilateral splenium of corpus callosum(SC)and positive correlation between WM volume and FA in the right SC,increased FA in WM of the left postcentral gyrus(Po CG)and the region above left insula(INS),right hippocampus(HIP)and negative correlation between FA and MD in these brain regions,and increased average FA values,average length and number of streamlines in WM tracts via the left Po CG and INS,and increased average FA values,average length of streamlines in WM tracts via the right HIP.Conclusions:1.There are differences in both brain function and structure in several brain regions between LH and RH adults,not only in macrostructure but also in microstructure of brain WM.2.Increased brain GM volume and brain functional activity in the left IPG may be related to the stronger spatial cognitive ability of LH adults.3.There are decreased brain WM volume and significantly positive correlation between brain WM volume and FA in the right SC in LH adults which suggest there may be some certain correlations between macro-and micro-structure changes in human brain underlying handedness-related cognition and behavior.4.The left preCun have much stronger brain activity and more functional connectivity with other brain regions,indicating that the pre Cun maybe a powerful neural hub in LH adults.5.There are higher FA values in WM of the left Po CG and right HIP,with better compactness,integrity,and parallelism in fiber bundle via these brain regions,respectively,suggesting that daily behavior habits may have impacts on WM developmental plasticity in human being.