Sexual dimorphism in the corpus callosum: methodological considerations in MRI morphometry

Area of Science:

• Neuroanatomy
• Neuroimaging
• Human anatomy

Background:

• Sexual dimorphism in the corpus callosum (CC) is well-documented.
• Previous studies show inconsistent findings due to varied measurement and normalization techniques.
• Understanding these variations is crucial for accurate interpretation of CC morphology.

Purpose of the Study:

• To evaluate the impact of different normalization strategies on the assessment of sexual dimorphism in the corpus callosum (CC).
• To demonstrate how varying data manipulations can yield discordant results from the same raw magnetic resonance imaging (MRI) data.
• To compare the effectiveness of stereotaxic, ratio, and covariate methods in normalizing CC area for brain size differences.

Main Methods:

• Midsagittal corpus callosum (CC) area was measured from MRIs of 137 healthy young adults.
• Three normalization strategies (stereotaxic, ratio, covariate) were applied.
• Five different normalization variables were used in conjunction with these strategies.

Main Results:

• Males exhibited significantly larger absolute total CC area, anterior third, and posterior midbody.
• Females showed relatively larger total CC area, anterior midbody, and splenium when using stereotaxic and ratio normalization methods.
• The covariate method did not reveal significant sex differences in CC area at the 0.05 significance level.

Conclusions:

• Normalization and analysis methods are not interchangeable and significantly influence findings on CC sexual dimorphism.
• The choice of normalization strategy critically affects the interpretation of relative CC size differences between sexes.
• Further research should standardize normalization techniques to ensure consistent and reliable results in neuroimaging studies.