The Relationship of Verbal Working Memory and Theory of Mind in First Degree Relatives of Patients With Schizophrenia and Bipolar Disorder

Objective: We aimed to compare Theory of Mind (ToM) functions and investigate the relationship between ToM functions and verbal working memory (VWM) in first degree relatives of bipolar disorder and schizophrenia patients. Method: The sample consisted of first degree relatives of patients with bipolar disorder (n=22), schizophrenia (n=28), and age, gender, education and total IQ matched healthy volunteers (n=27) without a family history of schizophrenia or bipolar disorder. We administered Auditory Consonants Test (ACT) to evaluate VWM, first and second order false belief tests (ToM-1, ToM-2), Faux Pas Test (FPT), Hinting Test (HT) to evaluate different domains of ToM functions. Results: Both relative groups performed significantly lower in all components of ToM and VWM tests compared to the control group. When VWM scores were employed as covariate in the analyses, the FPT difference between the groups remained significant, HT difference regressed to a marginal level, and the difference between ToM-1 and ToM-2 disappeared. Conclusion: To our knowledge, this is the first study indicating the presence of ToM impairment among first degree relatives of bipolar disorder patients similar to relatives of schizophrenia patients. VWM performance seems to affect first and second order ToM functions in relatives of patients with schizophrenia and bipolar disorder. On the other hand, FPT and HT domains seem to be independent of VWM performances in these groups. FPT and HT impairments may be familial vulnerability markers that are independent from neurocognitive impairment.