Background: Bipolar affective disorder patients often show cognitive deficits that are similar to those found in schizophrenia patients. Theory of mind (the ability to understand others' mental states) is compromised in currently ill schizophrenia patients. This study aimed to establish whether similar deficits are found in bipolar patients.
Methods: We measured theory of mind ability in 20 bipolar-manic patients, 15 bipolar-depressed patients, 13 bipolar patients in remission and 15 normal controls. The task, which controlled for memory and comprehension, had previously been used in a study of schizophrenia patients.
Results: Impaired performance on theory of mind was found for both bipolar-depressed and bipolar-manic patients, even when memory was controlled for. No impairment was observed in the remitted patients.
Limitations: The manic patients scored lower than the remitted patients on a brief measure of intelligence; no other group differences in IQ were significant.
Conclusions: Theory of mind deficits are found in currently symptomatic bipolar patients. These findings add to growing evidence that common mechanisms may contribute to bipolar affective disorder and schizophrenia.