Theory of mind deficits in bipolar affective disorder

Abstract

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.

Introduction

Although cognitive deficits have been extensively studied in patients suffering from nonaffective psychoses (Green, 1998) they have been relatively neglected in studies of bipolar affective disorder. When those efforts have been made, similarities between schizophrenia and bipolar patients have been more apparent than differences. For example, bipolar patients have been found to perform poorly on the digit span with distraction task (Oltmanns and Neale, 1978), the backward masking task (Fleming and Green, 1995), the continuous performance test (Nuechterlein et al., 1991) and on other measures of attention (Serper, 1993) that are commonly compromised in schizophrenia.

Recently, research has focused on the possibility that impairments in the ability to understand others mental states may play a role in some schizophrenia symptoms. People who have this ability (which is known to be permanently impaired in autism; Happé, 1994) are said to possess a ‘theory of mind’ or ToM (Baron-Cohen, 1995). Frith (1994) has argued that problems of meta-representation in general, and theory of mind in particular, may be present during acute psychotic episodes, and may be linked specifically to paranoid symptoms and negative behavioural signs, and has found evidence consistent with this hypothesis (Corcoran et al., 1995, Corcoran et al., 1997, Frith and Corcoran, 1996, Doody et al., 1998). However, the specificity of these findings for particular symptoms remains a source of controversy. Drury et al. (1998) found no difference between paranoid and nondeluded patients on a series of ToM tasks, although some evidence was found that schizophrenia patients performed more poorly than a mixed group of psychotic patients who were assigned diagnoses other than schizophrenia. Sarfati et al. (1997) found strong associations only between ToM dysfunction and formal thought disorder, while Langdon et al. (1997) found evidence of ToM problems in groups of psychotic patients with negative features but not in patients with paranoid delusions.

Theory of mind deficits have not been adequately explored in psychiatric disorders other than schizophrenia. None of the ten psychotic controls in the study performed by Drury et al. (1998) had a diagnosis of bipolar disorder. In the study by Doody et al. (1998), ToM deficits were not observed in a group of affective disorder patients but, again, only two out of the 12 participants in this group were diagnosed as suffering from bipolar disorder. In this paper, we report a comparison of bipolar-manic, bipolar depressed, bipolar-remitted and normal individuals, using a ToM task previously used by Frith and Corcoran (1996) in a study of schizophrenia patients.