Abstract
The left and right sides of the human brain are specialized for different kinds of information processing, and much of our cognition is lateralized to an extent toward one side or the other. Handedness is a reflection of nervous system lateralization. Roughly ten percent of people are mixed- or left-handed, and they show an elevated rate of reductions or reversals of some cerebral functional asymmetries compared to right-handers. Brain anatomical correlates of left-handedness have also been suggested. However, the relationships of left-handedness to brain structure and function remain far from clear. We carried out a comprehensive analysis of cortical surface area differences between 106 left-handed subjects and 1960 right-handed subjects, measured using an automated method of regional parcellation (FreeSurfer, Destrieux atlas). This is the largest study sample that has so far been used in relation to this issue. No individual cortical region showed an association with left-handedness that survived statistical correction for multiple testing, although there was a nominally significant association with the surface area of a previously implicated region: the left precentral sulcus. Identifying brain structural correlates of handedness may prove useful for genetic studies of cerebral asymmetries, as well as providing new avenues for the study of relations between handedness, cerebral lateralization and cognition.
Highlights
Handedness is perhaps the most overt reflection of lateralization of the central nervous system in humans
At the time of this study the Brain Imaging Genetics (BIG) subject-pool consisted of 2337 self-reported healthy individuals (1248 females) who had undergone anatomical (T1-weighted) MRI scans, usually as part of their involvement in diverse smaller-scale studies at the Donders Centre for Cognitive Neuroimaging (DCCN), and who had given their consent to participate in BIG
In a large sample of primarily young adult and healthy individuals, we tested for associations of handedness with total and regional measures of hemispheric cerebral cortical surface area
Summary
Handedness is perhaps the most overt reflection of lateralization of the central nervous system in humans. 90% of humans are right-handed, while even other primates (e.g., chimpanzees and macaques) do not show such a strong degree of populationlevel handedness (Lonsdorf and Hopkins, 2005; Meunier et al, 2013). This motor asymmetry is observable at least as early during human development as 15 weeks of gestation, and is preceded by asymmetries of arm movements even earlier (Hepper, 2013). Knecht and colleagues found an increased incidence of bilateral and right hemisphere language lateralization among left-handers, compared to righthanders, the majority of left/mixed handers still showed left-hemisphere language dominance (Knecht et al, 2000a,b) This suggests that developmental mechanisms affecting cerebral language dominance overlap to an extent with those influencing hand motor control. It remains poorly understood how these different domains of functional lateralization are related to each other (Badzakova-Trajkov et al, 2010)
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