Brain structural and functional asymmetry in human situs inversus totalis
Magnetic resonance imaging was used to investigate brain structural and functional asymmetries in 15 participants with complete visceral reversal (situs inversus totalis, SIT). Language-related brain structural and functional lateralization of SIT participants, including peri-Sylvian gray and white matter asymmetries and hemispheric language dominance, was similar to those of 15 control participants individually matched for sex, age, education, and handedness. In contrast, the SIT cohort showed reversal of the brain (Yakovlevian) torque (occipital petalia and occipital bending) compared to the control group. Secondary findings suggested different asymmetry patterns between SIT participants with (n = 6) or without (n = 9) primary ciliary dyskinesia (PCD, also known as Kartagener syndrome) although the small sample sizes warrant cautious interpretation. In particular, reversed brain torque was mainly due to the subgroup with PCD-unrelated SIT and this group also included 55% left handers, a ratio close to a random allocation of handedness. We conclude that complete visceral reversal has no effect on the lateralization of brain structural and functional asymmetries associated with language, but seems to reverse the typical direction of the brain torque in particular in participants that have SIT unrelated to PCD. The observed differences in asymmetry patterns of SIT groups with and without PCD seem to suggest that symmetry breaking of visceral laterality, brain torque, and language dominance rely on different mechanisms.
KeywordsBrain asymmetry Situs inversus Primary ciliary dyskinesia Language dominance Handedness
This study was funded by the Fonds Wetenschappelijk Onderzoek-Vlaanderen by FWO-grant n° G.0114.16N assigned to the first author. The authors would like to express their gratitude to the participants with situs inversus and control participants who took part in the study. We also want to thank the colleagues who contributed to the recruitment of SI and control participants, scoring of the behavioral data, or rating of the anatomical data: Eric Achten, Charlotte Boeykens, Charlotte Christiaens, Mattias De Coninck, Kirsty Gray, Peter Mariën, Emma Pauwels, and Sylke Vanrietvelde.
Compliance with ethical standards
This study was funded by the Fonds Wetenschappelijk Onderzoek-Vlaanderen by FWO-Grant No. G.0114.16N assigned to the first author.
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
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