Left-Handers Are Less Lateralized Than Right-Handers for Both Left and Right Hemispheric Functions.

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neuroimaging

Background:

• Cerebral asymmetries for language are well-documented, with most right-handers exhibiting typical left-hemisphere dominance.
• Previous research often compares handedness groups using central tendency measures, potentially masking individual variations in lateralization.

Purpose of the Study:

• To investigate differences in the degree of cerebral lateralization between left- and right-handers across multiple cognitive functions.
• To test whether reduced mean lateralization in left-handers is due to reversed asymmetry or generally reduced asymmetry.

Main Methods:

• Used functional magnetic resonance imaging (fMRI) localizer paradigms to assess hemispheric dominance.
• Matched left- and right-handers for hemispheric dominance across verbal fluency, face, body, and scene perception tasks.
• Compared the degree of dominance between groups using t-tests on laterality indices.

Main Results:

• Left-handers with typical cerebral asymmetries demonstrated less lateralization for language, face, and body perception compared to right-handers.
• This reduced lateralization was observed even when hemispheric dominance was matched between groups.

Conclusions:

• The findings suggest that left-handers, even those with typical asymmetry patterns, exhibit less pronounced lateralization across several cognitive functions.
• These results present a challenge to current theories explaining language lateralization and the neurobiological basis of handedness.