Brain (A) symmetry in monozygotic twins

Area of Science:

• Neuroscience
• Human genetics
• Developmental biology

Background:

• The origins and development of human brain laterality, particularly handedness, remain largely unknown.
• Brain laterality, the asymmetrical organization of cognitive functions, is a hallmark of the human brain.
• The planum temporale is a key brain structure associated with language and functional laterality.

Purpose of the Study:

• To investigate the genetic and environmental influences on brain laterality using monozygotic twins.
• To examine the relationship between cerebral hemispheric asymmetry of the planum temporale and handedness.
• To explore the ontogenetic models that explain discordance in brain lateralization within twin pairs.

Main Methods:

• Utilized in vivo magnetic resonance morphometry to measure cerebral hemispheric asymmetry of the planum temporale.
• Analyzed pairs of monozygotic twins, both concordant and discordant for handedness.
• Calculated intraclass correlations to assess the similarity of planum temporale asymmetry within twin pairs.

Main Results:

• Intraclass correlations for planum temporale asymmetry were low in both concordant and discordant monozygotic twin pairs.
• Right-handed individuals exhibited significant leftward asymmetry of the planum temporale.
• Left-handed individuals showed a lack of significant planum temporale asymmetry.
• Observed discordance in lateralized brain anatomy suggests a role for non-genetic factors in utero.

Conclusions:

• The findings confirm a strong coupling between the lateralized structure (planum temporale asymmetry) and function (handedness) of the human brain.
• Early epigenetic factors, acting differentially within twin pairs in utero, likely play a crucial role in the development of anatomofunctional laterality.
• The study provides evidence supporting ontogenetic models that incorporate both genetic and non-genetic influences on brain lateralization.