Theory of mind in schizophrenia: a comparison of subgroups with low and high IQ

Background: Social cognitive impairment is common in schizophrenia, but it is unclear if it is present in individuals with high IQ. This study compared theory of mind (ToM) in schizophrenia participants with low or high IQ to healthy controls. Methods: One hundred and nineteen participants (71 healthy controls, 17 high IQ (IQ ≥115), and 31 low IQ (IQ ≤95) schizophrenia participants) were assessed with the Movie for the Assessment of Social Cognition, providing scores for total, cognitive, and affective ToM, along with overmentalizing, undermentalizing, and no-mentalizing errors. IQ was measured with Wechsler Abbreviated Scale of Intelligence; clinical symptoms with the Positive and Negative Syndrome Scale. Results: Healthy controls performed better than the low IQ schizophrenia group for all ToM scores, and better than the high IQ schizophrenia group for the total score and under- and no-mentalizing errors. The high IQ group made fewer overmentalizing errors and had better total and cognitive ToM than the low IQ group. Their number of overmentalizing errors was indistinguishable from healthy controls. Conclusion: Global ToM impairment was present in the low IQ schizophrenia group. Overmentalizing was not present in the high IQ group and appears related to lower IQ. Intact higher-level reasoning may prevent the high IQ group from making overmentalizing errors, through self-monitoring or inhibition. We propose that high IQ patients are chiefly impaired in lower-level ToM, whereas low IQ patients also have impaired higher-level ToM. Conceivably, this specific impairment could help explain the lower functioning reported in persons with intact IQ.