Brain structural and functional asymmetry in human situs inversus totalis

Area of Science:

• Neuroscience
• Human Anatomy
• Medical Imaging

Background:

• Situs inversus totalis (SIT) is a rare condition involving complete reversal of visceral organs.
• Brain asymmetry, including language lateralization and brain torque, is a key area of neurodevelopmental research.
• The relationship between visceral asymmetry and brain asymmetry remains incompletely understood.

Purpose of the Study:

• To investigate brain structural and functional asymmetries in individuals with situs inversus totalis (SIT).
• To compare language-related brain lateralization and brain torque between SIT participants and controls.
• To explore potential differences in asymmetry patterns between SIT participants with and without primary ciliary dyskinesia (PCD).

Main Methods:

• Magnetic resonance imaging (MRI) was employed to assess brain structure and function.
• Fifteen participants with SIT were compared to fifteen matched control participants.
• Analysis focused on peri-Sylvian gray and white matter asymmetries, hemispheric language dominance, and Yakovlevian brain torque.

Main Results:

• Language-related brain structural and functional asymmetries were similar between SIT participants and controls.
• A reversal of typical Yakovlevian brain torque was observed in the SIT cohort compared to controls.
• Secondary analyses suggested different asymmetry patterns in SIT participants with and without PCD, with reversed torque more pronounced in those without PCD.

Conclusions:

• Complete visceral reversal (SIT) does not affect the lateralization of language-associated brain asymmetries.
• SIT appears to reverse the typical direction of brain torque, particularly in individuals without PCD.
• Symmetry breaking mechanisms for visceral laterality, brain torque, and language dominance may differ.