Theory of mind (ToM) deficits, difficulties in recognizing the intentions, propensities, and beliefs of others have been shown in individuals with bipolar disorder in several studies; however, it is not yet elucidated how ToM abilities changes over the course of bipolar disorder and is related to illness symptoms. This is one of the first longitudinal studies to compare the ToM abilities of euthymic bipolar individuals and healthy controls over a four and a half years period. ToM abilities were measured using the Reading the Mind in the Eyes Test (RMET). A total of 91 euthymic bipolar individuals and 91 healthy controls were included in the analyses. Linear mixed models were used to compare ToM abilities of bipolar individuals and healthy controls. It was found that bipolar individuals scored lower on average on the RMET than healthy controls and that these RMET scores were stable over four and a half years. The results of this study suggest that ToM deficits are a stable (possibly endophenotypic) trait of bipolar disorder. This understanding can contribute to better identification, assessment, and treatment strategies for individuals with bipolar disorder, ultimately improving their overall care and outcome.

Theory of mind abilities during the course of bipolar disorder: a longitudinal study using mixed models