Prose memory deficits associated with schizophrenia
Introduction
There is a close relationship between language functioning and schizophrenia, and verbal memory is a legitimate and important deficit with significantly negative consequences for real world social functioning, in terms of social problem-solving or social skill acquisition (Green, 1996). Over the past years, researchers have proposed that some forms of memory are selectively impaired in schizophrenia (e.g., Saykin et al., 1991, Saykin et al., 1994, Gourovitch and Goldberg, 1997, Cirillo and Seidman, 2003). From a neuro-anatomical perspective, the dysfunction in the prefrontal cortex and the hippocampus/parahippocampal regions (for a review see: Cirillo and Seidman, 2003, Elvevåg et al., 2004), with their possible functional connectivity, could explain the pattern of verbal memory deficits in schizophrenia. Furthermore, frontal brain damage has been suggested to explain schizophrenia by both neuropsychological (e.g. Gourovitch et al., 1996) and neuroimaging studies (e.g. Heckers et al., 2000). Frontal lobe dysfunction would give rise to problems in encoding information, hence, learning, memory for temporal sequence, recognition memory, and commission of distortions.
In episodic memory research, a distinction between the ‘content’ and ‘context’ of memory events is often made. “Content” refers to the event itself, such as the recall accuracy, whereas information about context usually refers to extrinsic features that are not part of the stimulus itself, such as its temporal context (Waters et al., 2004). Memories require not only retaining particular features but also the cognitive processes for binding the ‘content’ and ‘context’ together to form a complete memory representation (Chalfonte and Johnson, 1996). In this connexion, Guillem et al. (2001) reported that information integration among people with schizophrenia was impaired. Waters and colleagues (2004) observed that people with schizophrenia tended to have a more fractionated recollection of the recalled events. Several other authors have also proposed that many of the cognitive deficits observed in schizophrenia result from an impairment in the ability to process contextual information (e.g., Bazin et al., 2000, Cohen and Servan-Schreiber, 1992, Rizzo et al., 1996a, Servan-Schreiber et al., 1996).
Although assessing verbal memory via a list-learning format provides a useful means for understanding how content-related information is processed,(i.e. accuracy of items recalled), studying of prose memory, on the other hand, offers a unique avenue for understanding how verbal information acquired is organized and integrated to form a meaningful memory representation. In view of the current neuropsychological approach, assessment of prose memory has mostly emphasized the accuracy of story recall. This approach, however, does not fully address other processing deficits that have been observed (Lee et al., 2004). For example, the encoding process of patients with frontal lobe lesions (Cunningham et al., 1997) or other brain lesion victims (Lezak, 2005) was often interfered with by substantial confabulation or perseverated introjections, that affect the use of the newly learned information for higher cognitive manipulation. Thus far, only one study has examined prose memory functioning in patients with schizophrenia (Clare et al., 1993). Their study, however, did not include the use of recognition and intrusion (a measure of confabulation). Guillem et al. (2001) observed that patients with schizophrenia might have problems in integrating information for conceptual sequences and contexts. Lee et al. (2004) suggested that, for studying prose memory, the process of prose memory, namely encoding, storage (retention), retrieval (Weiss and Heckers, 2001), as reflected in the performance of recall accuracy, rate of forgetting/retention, and recognition accuracy, respectively (Perry et al., 2000), should be examined to understand the nature of verbal contextual memory deficit.
No studies thus far have examined whether the various components of prose memory are differentially impaired in patients with schizophrenia compared with healthy controls and how the learning phase and delay phase would exert an impact on the recall pattern of the subjects if the various constructs are found to be differentially impaired. Most studies have consistently demonstrated impaired recall accuracy on verbal memory tasks (both word-list learning and story recall tasks), in schizophrenia patients during the initial learning, owing to deficits in the encoding stage. Nevertheless, only a few studies, and with contradictory results, have been concerned with the retention and forgetting in these patients during the storage stage. Also, many studies have investigated recognition accuracy in patients with schizophrenia, but a scarce number of studies have been devoted to the commission of false recognition in these patients compared with healthy controls. Impaired memory for the temporal order of events has been demonstrated in patients with schizophrenia, but memory for the order of events has not been thoroughly examined (Elvevåg et al., 2003). In any case, studies are lacking that investigate the performance in temporal sequence accuracy among schizophrenia patients after repeated learning trials and a delay period. Similarly, while few studies have examined commission of distortions in patients with schizophrenia in immediate recall (e.g., Nathaniel-James and Frith, 1996), no studies have examined the pattern of distortion commissions across different recall trials after the learning and delay phases. Moreover, studies are lacking that investigate the performance of patients with schizophrenia on the various processes of prose memory.
To understand the nature of contextual verbal memory impairment that may be associated with schizophrenia, we used memory of prose as a medium and studied how the illness differentially affected the various processes of contextual verbal memory. The processes of prose memory that were studied included recall accuracy, temporal sequence accuracy, and distortions. The rates of learning, forgetting, and retention were also examined. We speculated that patients with schizophrenia would have a poorer performance compared with healthy controls on all constructs studied, with the exception of false recognition, in which healthy controls were hypothesized to commit a greater number of false positives in the recognition task of the prose passage.
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Participants
A total of 39 in-patients with chronic schizophrenia at the United Christian Hospital Psychiatric Day Center were diagnosed by a licensed psychiatrist according to the International Classification of Disease (ICD-10). Along with these patients, 39 healthy controls, matched for chronological age, sex, and years of education were recruited for the present study. Exclusion criteria, applied to all clinical and healthy control participants, included a history of significant head trauma or
Characteristics of participants
The group consisted of 18 males and 21 females. The clinical characteristics of patients with schizophrenia are reported in Table 1. Patients with schizophrenia had a mean number of admissions to hospital of 1.90 (SD = 1.45) and a mean duration of illness of 8.85 years (SD = 7.66). The patients had a mean SAPS score of 6.15 (SD = 6.58) and a mean SANS score of 9.59 (SD = 8.91). Patients with schizophrenia and their respective healthy controls were not statistically different from each other in terms of
Discussion
Prose memory deficits were observed in people with schizophrenia. Results from the present study show that patients with schizophrenia performed poorer on recall accuracy and temporal sequence accuracy only during the first immediate recall, and on recognition accuracy, compared to healthy counterparts. Furthermore, schizophrenia patients had a significantly higher rate of learning across the five learning trials and higher commission of distortions during the delayed recall, than did the
Acknowledgements
This work is supported by University Development Fund of The University of Hong Kong.
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