Cognitive, neuroimaging, and genetic insights on the interthalamic adhesion from a large cohort study of 591 subjects.

Both thalami can be connected by the Interthalamic Adhesion (IA), a white matter tract that crosses the 3rd ventricle. Its presence varies among individuals and remains poorly understood. This study examines the IA's prevalence, anatomical variations, genetic determinants, and cognitive associations. Data from 591 healthy subjects (25-35 years) from the Human Connectome Project were analyzed, and grouped into monozygotic (MZ) or dizygotic (DZ) twins, non-twin siblings, and unrelated individuals. MRI was used to characterize the IA, while neuropsychological assessments and Freesurfer parcellations were used to assess cognition and anatomical differences between subjects with or without an IA. The IA was absent in 12.7% of subjects, more commonly in males (20.0%) than females (6.3%). No significant differences in age, education, or cognition were found between individuals with or without an IA. IA absence was associated with increased cerebrospinal fluid volumes, enlarged third ventricles, and thinning in several cortical areas. Genetic analysis on the IA presence or absence revealed a heritability estimate of 34% with a higher concordance among MZ twins (96%) than in other groups. The remaining 4% discrepancy was observed in male pairs only. This study underscores the genetic basis of IA, highlighting sexual dimorphism and neuroanatomical differences associated with its absence, despite unaffected cognition in healthy individuals.