Cortical thickness correlates of psychotic experiences: Examining the effect of season of birth using a genetically informative design

• MRI twin study on cortical thickness, psychotic experiences (PEs) and seasonality.
• Healthy individuals with high PEs displayed cortical thickening.
• This cortical thickening is in line with theories of compensatory brain features.
• The cortical thickness–PEs relationships may depend on birth season.
• Effects may be driven by familial factors influencing PEs and cortical morphology.

Season of birth has been shown to influence risk for several neuropsychiatric diseases. Furthermore, it has been suggested that season of birth modifies a number of brain morphological traits. Since cortical thickness alterations have been reported across some levels of the psychosis-spectrum, this study was aimed at i) assessing the scarcely explored relationship between cortical thickness and severity of subclinical psychotic experiences (PEs) in healthy subjects, and ii) evaluating the potential impact of season of birth in the preceding thickness–PEs relationship. As both PEs and brain cortical features are heritable, the current work used monozygotic twins to separately evaluate familial and unique environmental factors.High-resolution structural MRI scans of 48 twins (24 monozygotic pairs) were analyzed to estimate cortical thickness using FreeSurfer. They were then examined in relation to PEs, accounting for the effects of birth season; putative differential relationships between PEs and cortical thickness depending on season of birth were also tested.Current results support previous findings indicative of cortical thickening in healthy individuals with high psychometrically assessed psychosis scores, probably in line with theories of compensatory aspects of brain features in non-clinical populations. Additionally, they suggest distinct patterns of cortical thickness–PEs relationships depending on birth seasonality. Familial factors underlying the presence of PEs may drive these effects.