Reduced levels of specific autobiographical memories in schizophrenia

Abstract

Autobiographical memory is intrinsically related to the self and personal identity. This study investigated whether both personal episodic memory and semantic memory are impaired in schizophrenia, a disease characterized by an abnormal personal identity. Personal episodic memory and personal semantic memory were investigated in 24 patients with schizophrenia and 24 normal subjects using an autobiographical fluency task and an autobiographical memory inquiry. Autobiographical memory scores and the proportion of specific memories were lower in patients with schizophrenia than in normal subjects. The deficit of personal episodic and semantic memory, as assessed by the autobiographical memory inquiry and the autobiographical fluency task, respectively, was most apparent after the onset of clinical symptoms. Schizophrenia is associated with an impairment of both personal episodic and semantic memory and with a reduction of specific autobiographical memories. Those impairments are consistent with the existence of an abnormal personal identity in patients with schizophrenia.

Introduction

Autobiographical memory relates to the capacity of people to recollect personal events and facts, (e.g. one's name) from their lives. It is an inherent part of personal identity and is strongly related to its development (Conway and Pleydell-Pearce, 2000). Personal episodic memory refers to single events, while personal semantic memory refers to facts. Surprisingly, only a few studies have been devoted to the investigation of autobiographical memory in schizophrenia, a disease characterized by an abnormal personal identity, while numerous studies have shown that episodic and semantic memory are impaired in this disease, (e.g. Tamlyn et al., 1992, Clare et al., 1993, Goldberg and Gold, 1995, Joyce et al., 1996, Goldberg et al., 1998, Aleman et al., 1999). Tamlyn et al. (1992) investigated four patients with schizophrenia using the Autobiographical Memory Inventory (AMI, Kopelman et al., 1990). Autobiographical memory was impaired in childhood, early adult life and the recent period, with relative sparing of more remote memories. Feinstein et al. (1998) studied 19 patients with schizophrenia and 10 normal controls using the same inventory. Both personal episodic memory and personal semantic memory were impaired. Moreover, whereas normal controls exhibited high and equivalent performance across childhood, early adulthood and the recent period, patients exhibited a U-shaped profile of performance. Poorest performance was observed in the early adult period, corresponding to the onset period of schizophrenia, while the childhood period was the least impaired. Finally, Baddeley et al. (1995) explored five deluded and five non-deluded patients using the AMI. Both the deluded and non-deluded groups were normal in their ability to recall autobiographical facts from their earlier life. However, non-deluded patients produced less specific memories than deluded patients. There was no evidence that the impairment was particularly marked after the onset of the disease. Therefore, whereas all three studies provided converging evidence that autobiographical memory is impaired in schizophrenia, their conclusions differed as to whether personal semantic memory is defective and whether there is an aggravation of the memory impairment after the onset period of schizophrenia.

Our study explored autobiographical memory in schizophrenia with reference to the model of autobiographical memories put forward recently by Conway and Pleydell-Pearce (2000). This model is unique in that it brings together autobiographical memories, the self and personal identity. Autobiographical memories are transitory mental constructions generated from an autobiographical knowledge base. Autobiographical knowledge is held in this base at different levels of specificity, the most specified level being that of highly specific single details, such as the sensory and perceptual details of a particular event. The model also postulates that the formation of autobiographical memories is controlled by a set of structured goals, the working self. Conway and Pleydell-Pearce introduced this term to create a direct link with the concept of working memory developed by Baddeley (1986) as a set of control, strategic processes. Through its current goals, motivation and desires, the working self functions as a control process that coordinates and modulates the encoding and the retrieval of autobiographical memories. Specific memories often arise in response to experiences of goal attainment or goal failure. They create what subjects regard as themselves insofar as they are able to recognize themselves in these goals and desires. Therefore, specific memories convey a sense of personal identity that is stable across various lifetime periods. The model of Conway and Pleydell-Pearce (2000) makes it possible to relate the impairment of autobiographical memories reported in schizophrenia to abnormalities of personal identity, a crucial, albeit neglected, area of schizophrenia research. Abnormalities of personal identity emerge at the onset period of schizophrenia, which occurs in adolescence and early adulthood, that is, when the autobiographical knowledge is being acquired, organized and consolidated to form personal identity. In keeping with the model of Conway and Pleydell-Pearce (2000), the occurrence of the illness during this critical lifetime period is consistent with the hypothesis that the construction of personal identity may be impaired, per se, in patients with schizophrenia.

While strategic processes play a crucial role in the formation of autobiographical memories both in encoding and in retrieval, there is converging evidence that these processes are defective in patients with schizophrenia (Russel et al., 1975, Russel and Beekhuis, 1976, Traupmann et al., 1976, Huron et al., 1995, Danion et al., 1999). Therefore, defective encoding or retrieval processes are two equally plausible mechanisms that may be responsible for autobiographical memory dysfunction in schizophrenia. The autobiographical memory dysfunction may be related to a defect of the strategic processes involved in retrieval, when the memory is being generated from the autobiographical knowledge base. It may also be related to a defect of the processes involved in encoding, provided that the illness process is already present when the personal event to be memorized occurs. Therefore, two different patterns of autobiographical memory dysfunctions might be predicted: (1) Patients with schizophrenia would exhibit an overall reduction of personal episodic and semantic memories throughout all lifetime periods, parallel to that of the control group. This pattern would be inconclusive as regards the underlying mechanism; indeed, it may reflect a defect of retrieval processes, but it may also reflect a defect of encoding processes if schizophrenia is viewed as a neurodevelopmental disease with cognitive dysfunctions present early in life, long before illness onset (Marenco and Weinberger, 2000). (2) Patients would exhibit an additional impairment of autobiographical memories from a particular lifetime period, as evidenced by a statistically significant interaction between groups and periods. Such a pattern would support the hypothesis that poorer memories resulted from encoding deficits that had been present at least since this particular period.