Hand preference and the corpus callosum: Is there really no association?

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Human Anatomy

Background:

• A long-held belief in cognitive neuroscience suggests the corpus callosum is larger in non-right-handers.
• Previous meta-analyses have challenged this, but were limited by data resolution and confounding factors like brain size.

Purpose of the Study:

• To investigate handedness-related differences in corpus callosum size and morphology.
• To address limitations of previous studies by controlling for brain size and using high-resolution analysis.

Main Methods:

• Analysis of midsagittal corpus callosum in 1057 participants from the Human Connectome Project (HCP).
• Comparison of handedness groups based on consistency and direction of hand preference.
• Accounting for forebrain volume (FBV) as a covariate and using relative area (callosal area/thickness / FBV).
• High-resolution analysis of callosal thickness at 100 points.

Main Results:

• No significant handedness-related differences were found in corpus callosum area or thickness.
• Effect sizes for differences between mixed-handers and consistent right-handers were small (Cohen's d < 0.1 for area, < 0.2 for thickness).
• Confidence intervals excluded meaningful effects (|d| < 0.2 for area, < 0.3 for thickness).

Conclusions:

• Hand preference has a minimal effect on corpus callosum morphology, with effect sizes smaller than those for age or sex.
• The common practice of attributing cognitive or behavioral differences between handedness groups to callosal architecture is questionable.
• Future research should consider other factors influencing cognitive and behavioral variations.