Elsevier

Schizophrenia Research

Volume 60, Issue 1, 1 March 2003, Pages 57-64
Schizophrenia Research

Theory of mind and the role of IQ in chronic disorganized schizophrenia

https://doi.org/10.1016/S0920-9964(02)00162-7Get rights and content

Abstract

Background: Several studies have suggested a theory of mind (ToM) deficit in schizophrenic disorders. However, the role of interfering variables such as IQ, attention, memory, and severity of the disorder has remained ambiguous. Methods: A theory of mind picture story comprising a sequencing task, a first and a second order false belief test, and a tactical deception test was given to a group of 23 patients with chronic disorganized schizophrenia and to 12 healthy control persons. In addition, a nonsocial picture story had to be sequenced. Severity of the psychopathology was measured by using the brief psychiatric rating scale (BPRS), IQ was estimated using the ‘Mehrfachwahlwortschatztest’ (MWT, multiple choice verbal comprehension test). Results: The schizophrenic group was impaired relative to controls on the theory of mind task, but not on the sequencing task of the nonsocial picture story. However, when controlled for IQ, no such difference was found. These findings were neither related to severity, duration, nor age at onset of the disorder. Conclusions: Theory of mind deficits in schizophrenia may be related to domain general impairments, e.g., intelligence and working memory load, rather than reflecting a ‘genuine’ compromised mental state attribution similar to autistic spectrum disorders. Schizophrenic patients may, however, rather be impaired in how and when to apply strategic social reasoning. Further studies to investigate the nature of social deficiency in schizophrenia are warranted.

Introduction

Theory of mind is defined as the ability to infer mental states, e.g., intentions and dispositions of other individuals. From an evolutionary perspective, theory of mind has been suggested to represent an essential component of social intelligence that evolved in primates to solve problems of an increasingly complex social environment Brothers, 1990, Whiten, 2000. The acquisition of mental state representations, including understanding false beliefs and deception, thereafter, has been considered crucial to actively manipulate other people's behavior in order to improve one's own social (and reproductive) success. In support of this assumption, it has been demonstrated that the volume of the nonvisual neocortex in primates is correlated with the group size of the respective species as a measure of social complexity, labeled as ‘social brain hypothesis’ (Dunbar, 1998).

With respect to psychopathology, it may be hypothesized that the specialization of the human brain on information processing from the social environment may have contributed to an enhanced susceptibility to dysfunction as the evolutionary ‘cost’ of the development of advanced ‘mind reading’ capacities (Brüne, 2001). Likewise, Frith and Frith (1999) propose that specific impairments of theory of mind abilities may occur in both developmental and acquired psychiatric disorders with characteristic lesions in a dedicated brain system which is probably located in the prefrontal and temporal cortex (see also Russell et al., 2000, Stuss et al., 2001). However, whereas there is good empirical evidence of theory of mind impairments in autistic spectrum disorders (e.g., Baron-Cohen, 1995), the present data are far more ambiguous with respect to schizophrenic disorders. Clinically, it is obvious that patients with schizophrenia have deficits in social skills. In addition, the classic Schneiderian first rank symptoms, such as thought insertion, thought withdrawal, and thought broadcasting as well as delusions of control and reference, intuitively suggest a compromised theory of mind (Sarfati, 2000). As early as 1958, Conrad outlined in his Gestalt-theoretical monograph “Die beginnende Schizophrenie” (the beginning schizophrenia) that the inability to change mental perspectives comprises the core feature of the very earliest stage of schizophrenic disorders (Conrad, 1979). On the contrary, however, Walston et al. (2000) have recently argued that an intact theory of mind mechanism may be essential for developing persecutory delusions, at least in ‘pure’ delusional disorders, since so-called “theory of mind” delusions may only occur if the capacity to make inferences about intentions of other persons is preserved. Similarly, Abu-Akel and Bailey (2000) suggest that schizophrenic patients with positive symptoms may even have a ‘hyper-theory of mind’.

To date, several studies have systematically addressed theory of mind abilities in schizophrenia. However, some difficulties remain on how to interpret their results, for instance, due to methodological problems such as interference with intelligence and general information processing capacity which may, among other factors, depend on the acuteness and the chronicity of the disorder (Brüne, 2001). Furthermore, the majority of the samples assessed in the available studies were either relatively small or diagnostically heterogeneous, and hence limiting their comparability.

Section snippets

Brief review of theory of mind assessment in schizophrenia and rationale for the present explorative study

So far, the majority of studies of theory of mind (ToM) in schizophrenia have adopted short stories and picture sequences comprising first and second order false belief tasks similar to the methodology of ToM assessment in autism. Previous studies in schizophrenia have revealed differences in ToM comprehension according to symptom subgroups proposed by Frith (1992). It has been predicted, thereafter, that the performance of schizophrenic disorders on ToM tasks would be hierarchically formed

Subjects and tasks

Twenty-three patients (17 males, 6 females) who met the DSM-IV (American Psychiatric Association, 1994) criteria for disorganized schizophrenia were included. Acute exacerbation stages were excluded. The subjects were compared to 12 nonpsychiatric healthy controls (7 males, 5 females). IQ was estimated using the “Mehrfachwahlwortschatztest” (MWT, Lehrl, 1976; which may be best translated as ‘multiple verbal comprehension test’). Psychopathology was assessed using the brief psychiatric rating

Clinical and demographic characteristics

The age and sex distribution of the schizophrenic subjects and the control group are shown in Table 1. The groups did not differ with respect to age (F=0.093; p=0.762). In the schizophrenic group, the mean age at onset of the disorder was 18.8 years (S.D.=3.48) and the mean duration of illness was 10 years (S.D.=7.04). As expected, the schizophrenic group scored significantly higher on the BPRS compared to the nonpsychiatric group (F=86.457; p<0.001). Most significantly, there was a marked

Discussion

It is still a matter of debate as to what extent theory of mind is impaired in schizophrenia, although clinical intuition and the available studies clearly indicate that understanding other minds may be compromised, depending on the acuteness and the duration of the disorder Drury et al., 1998, Sarfati et al., 2000. Furthermore, recent studies suggest that ToM impairments appear to be related to the level of disorganization and psychomotor retardation Sarfati et al., 1999, Sarfati and

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