Theory of mind variability in schizophrenia: A neurodevelopmental perspective through neurological soft signs and premorbid adjustment.

Background: Theory of Mind (ToM) is impaired in individuals with schizophrenia (SZ). Given the neurodevelopmental nature of both social cognition and SZ, variations in ToM abilities likely originate early in life. Thus, indirect markers of altered neurodevelopment, such as neurological soft signs (NSS) and premorbid adjustment (PA), may help explain ToM differences. Methods: The study included 38 patients diagnosed with a schizophrenia-spectrum disorder (SSD), 26 healthy siblings and 47 controls. ToM was assessed using the Hinting Task (HT). NSS were evaluated with the Neurological Evaluation Scale (NES) and PA with the Premorbid Adjustment Scale (PAS), yielding Social and Academic scores. Intelligence Quotient (IQ, WAIS-III) and Family History (FH, Family Interview for Genetic Studies (FIGS)) were also assessed. Results: First, patients presented more deficits in two subscales of the NES (motor coordination and sequencing of complex motor acts) than siblings and controls, with siblings performing intermediate in the sequencing subscale. Patients showed worse social PA than siblings during childhood and late adolescence. Second, patients showed poorer HT performance than siblings and controls, but the neurodevelopmental markers did not modulate such differences. Third, within each group, neurodevelopmental vulnerability markers were not associated with ToM performance. Conclusion: In our sample, while patients showed more evidence of neurodevelopmental deviances than siblings and controls, such differences did not contribute to ToM variability. These results suggest a degree of independence between ToM and NSS/PA and that they could be potentially influenced by distinct neurodevelopmental mechanisms.