Looking for the agent: an investigation into consciousness of action and self-consciousness in schizophrenic patients

Abstract

The abilities to attribute an action to its proper agent and to understand its meaning when it is produced by someone else are basic aspects of human social communication. Several psychiatric syndromes, such as schizophrenia, seem to lead to a dysfunction of the awareness of one's own action as well as of recognition of actions performed by others. Such syndromes offer a framework for studying the determinants of agency, the ability to correctly attribute actions to their veridical source. Thirty normal subjects and 30 schizophrenic patients with and without hallucinations and/or delusional experiences were required to execute simple finger and wrist movements, without direct visual control of their hand. The image of either their own hand or an alien hand executing the same or a different movement was presented on a TV-screen in real time. The task for the subjects was to discriminate whether the hand presented on the screen was their own or not. Hallucinating and deluded schizophrenic patients were more impaired in discriminating their own hand from the alien one than the non-hallucinating ones, and tended to misattribute the alien hand to themselves. Results are discussed according to a model of action control. A tentative description of the mechanisms leading to action consciousness is proposed.

Introduction

A fundamental problem is raised by the mechanism of how one becomes aware of one's own actions, and how one's actions are distinguished from those of other people. This mechanism is critical for a number of reasons. First, the ability to make a distinction between the acting self and the acting other is one way by which the self feels distinct from other individuals and self-consciousness is built. Second, the ability to recognise the meaning of an action when it is produced by someone else and to attribute it to its proper agent is a basic function underlying human social communication.

Research on these points has been undertaken within several different frameworks. The study of mental and cognitive development is one of those. Researchers in this field have set the stage for a renewal of developmental studies, by demonstrating the appearance, in early childhood, of a special ability of the individual to attribute to others mental states differing from his/her own, and to infer the content of these mental states from his/her own mental content (the so-called `theory of mind', Leslie, 1987). The ability to imitate and to learn by observation is another critical developmental function, which might relate to the same basic mechanism (Meltzoff, 1995). This highly influential research has recently merged with other work in normal adult subjects, aimed at determining the neural mechanisms of mental representations, particularly in the context of action generation. The notions of internal models and internal simulation borrowed from computational neuroscience (see Wolpert et al., 1995) have now become a conceptual tool for studying the early stages of action generation, such as intending, for example. Experiments using brain mapping techniques have shown that merely observing an action performed by someone else is no less a powerful way of eliciting brain activity than other cognitive motor states, such as mentally simulating or preparing to execute that same action. These results (see Section 4) raise the point of the differences and similarities of motor representations activated during these states.

The study of mental disorders is another possible framework for understanding the problems of consciousness of action and self-consciousness. Some of the symptoms observed in schizophrenia, specifically the positive symptoms typical of the acute stage of the disease, seem to be relevant to a dysfunction of the awareness of one's own action and to a dysfunction of recognition of actions performed by others. One possible, general explanation for this difficulty would arise from a disability in attributing meaning to external events, itself due to a weakening of inhibitory processes crucial for consciously focusing attention (see Gray et al., 1991). Another, more specific, hypothesis is that of Frith, implying that schizophrenics fail in monitoring their willed intentions, including those related to the expression of thought (Frith, 1987; Frith, 1992). They fail to attribute elements arising from their long-term memory, from which they form their goals and plans, to their real origin. The consequence of this failure in monitoring makes them unable to disentangle `intentions' arising from external stimuli, from those generated as a consequence of their own cognitive functioning. Positive symptoms such as insertion of thought, hallucinations and delusion of control would directly derive from this difficulty.

Verbal hallucinations seem to be liable to this explanation. According to Frith (1996), the normal mechanism for attributing thought to its internal origin would be a comparison between the executive commands leading to speech and the anticipated sensory consequences of these commands. Normally, execution of the speech motor commands implies that the related sensory signals will be inhibited (Creutzfeldt et al., 1989). During verbal hallucinations in schizophrenic patients, by contrast, the sensory areas for language remain active, which suggests that the cancellation process does not operate. The nervous system in these patients behaves as if it were actually processing the speech of an external speaker. Hence their perception of their own thinking as originating from the outside world (Silbersweig et al., 1995; McGuire et al., 1996).

In the above situation, the patients attributed their own action to an external source. This tendency, however, only corresponds to part of the positive symptomatology in schizophrenia. The same patients may experience the reverse as well, i.e. they may experience the action of others as a consequence of their own intentions.

In the present study we compared groups of normal controls and of patients with and without positive symptoms, when required to make agency judgements about a hand movement originating either from themselves or from an experimenter. Our results showed that patients with hallucinations or delusional control, when faced with hand movements of uncertain origin (e.g. an alien hand performing the same movement as them), systematically considered the movements as theirs. This striking result raises the point of which cues are normally used for producing conscious judgements about the origin of an action.