Theory of mind impairments in euthymic bipolar patients

Abstract

Background

Deficits in social cognition, e.g. theory of mind (ToM) represent core characteristics involved in the etiology of psychopathological symptoms and an important predictor of social competence. In bipolar affective disorder, evidence for ToM deficits is scant, although brain imaging studies and impairments in non-social neurocognitive domains indicate deficits of prefrontal functions.

Methods

Twenty-nine euthymic patients with bipolar affective disorder and 29 matched healthy controls were examined with the ‘Movie for the Assessment of Social Cognition’ (MASC). Target parameters comprised 1) ‘cognitive’ and ‘emotional’ ToM scores, 2) qualitative analysis of errors brought about by ‘undermentalizing’ or ‘overmentalizing’ strategies and 3) non-social inferencing as a control factor.

Results

Patients compared to controls scored significantly lower for ‘cognitive’ (F = 9.417, df = 1, p = 0.003) but not for ‘emotional’ ToM. Bipolar patients showed significantly higher ‘undermentalizing’ (F = 4.830, df = 1, p = 0.032) but not ‘overmentalizing’ scores. A significant correlation (controlled for age) between the number of (hypo)manic episodes and ‘undermentalizing’ (r = 0.527, p = 0.030) as well as ‘emotional’ ToM (r = − 0.546, p = 0.023) was observed.

Limitations

Sample size did not allow for the analysis of medication effects.

Discussion

This is the first study of ToM in euthymic bipolar patients with a realistic video-based examination. Independently from basic cognitive dysfunctions, patients displayed a pronounced deficit in the cognitive domain of ToM with preserved emotional mentalizing abilities. The correlation with the number of manic episodes may indicate an increase of the deficit with disease progression. It can be assumed that social cognition reflects an important dimension of the persisting cognitive deficits in bipolar disorder with possible impact on disease outcome.

Introduction

Theory of mind (ToM; Premack and Woodruff, 1978) describes the ability to represent one's own or other's epistemic, volitional or emotional mental states. Patients with severe endogenous psychoses (Brüne, 2005) and developmental disorders like autism (Baron-Cohen et al., 2001) exhibit profound ToM deficits, which may result in a decline in social reciprocity and functional outcome (Green et al., 2000, Brüne et al., 2007).

Patients with unipolar major depression and mixed samples of unipolar and bipolar depression were also shown to exhibit ToM impairments, although these results did not remain undisputed (Lee et al., 2005, Inoue et al., 2004, Doody et al., 1998, Kettle et al., 2008). Some evidence indicates a higher relapse risk in patients with affective disorders and concomitant ToM deficits (Inoue et al., 2006).

In bipolar disorder, ToM impairments were reported in symptomatic and euthymic patients (Kerr et al., 2003, Olley et al., 2005, Lahera et al., 2008). However, in euthymic patients, the question whether ToM deficits are specific or secondary to non-social cognitive problems still remains open (Kerr et al., 2003). This aspect is crucial since neurocognitive deficits, like those of sustained attention, executive function and verbal memory, persist in the euthymic phase (Robinson and Ferrier, 2006, Robinson et al., 2006) and might represent endophenotypes of bipolar disorder (Bora et al., 2009, Arts et al., 2008).

However, evidence from neuroimaging research suggests a central role of a relative loss of prefrontal modulation of subcortical and medial temporal structures within the anterior limbic network resulting in dysregulations of mood in bipolar disorder (Strakowski et al., 2005, McIntosh et al., 2008). As these brain regions largely belong to the social cognitive network (Gallagher and Frith, 2003), mentalizing deficits may also be detected in bipolar disorder.

Studies in clinical conditions like Asperger Syndrome (Rogers et al., 2007, Dziobek et al., 2008), schizophrenia (Shamay-Tsoory et al., 2007, Montag et al., 2007) or brain lesions (Shamay-Tsoory et al., 2008) have reported dissociable deficits of cognitive and affective aspects of ToM. However, in bipolar disorder few studies attempted to dissect cognitive and affective ToM (Bora et al., 2005, Shamay-Tsoory et al., 2009).

In schizophrenic psychoses, excessive mental state attribution (‘overmentalizing’) has been implicated in the formation of paranoid symptoms (Frith, 2004), but ‘reduced’ mentalizing (‘undermentalizing’) may be more prominent in patients with negative symptoms (Brüne, 2005, Montag et al., submitted for publication). Differing mentalizing mechanisms may also be causative to the assumed mentalizing deficit in bipolar disorder, dependent on the presence of psychotic symptoms or general cognitive decline.

The present study investigates theory of mind functions in an outpatient sample of euthymic patients with bipolar disorder employing a naturalistic test, the Movie for the Assessment of Social Cognition (MASC; Dziobek et al., 2006). The MASC allows 1) to simultaneously investigate the recognition of cognitive and emotional mental state modalities and 2) a qualitative analysis of error responses. It was hypothesized that bipolar patients exhibit ToM deficits compared to healthy controls.