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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Schizophrenia Research, Volume 143, Issues 2–3, February 2013, Pages 285–290
Schizophrenia is associated with an impairment of prospective memory (PM) which refers to the ability to remember to carry out an intended action in the future. However, most of these studies were limited to chronic samples. The current study examined the event-based PM and time-based PM using a dual-task paradigm in 22 drug-naïve, first-episode psychosis (FEP) patients and 23 healthy controls. Results indicated that FEP patients performed significantly poorer than healthy controls in both event-based and time-based PM. However, the significant difference in time-based PM disappeared after controlling for working memory. Correlation analysis indicated that both types of PM did not correlate with positive symptoms or negative symptoms, duration of illness, or duration of untreated psychosis. However, time-based PM was correlated with the general psychopathology subscale of the PANSS. Taken together, these findings suggest that PM deficits are present in drug-naïve FEP patients; impairment of event-based PM appears to occur independently, whereas time-based PM impairment may be, in part, a secondary consequence of a working memory deficit.
Neurocognitive deficits are key features of schizophrenia (Elvevag and Goldberg, 2000 and Keshavan et al., 2008) and are a critical determinant of quality of life and functional outcome (Green et al., 2000, Kurtz et al., 2005, Matza et al., 2006 and Kurtz et al., 2008). Substantial evidence also suggests that patients with schizophrenia have deficits in a diverse array of cognitive domains, including working memory, language function, executive function, episodic memory, processing speed, attention, inhibition and sensory processing (Chan et al., 2004, Fioravanti et al., 2005, Chan et al., 2006b, Reichenberg and Harvey, 2007 and Mesholam-Gately et al., 2009). Within the context of generalized cognitive deficit, it has been suggested that the most severe impairments are episodic memory and executive control processes (Chan et al., 2004, Chan et al., 2006a, Chan et al., 2006b and Reichenberg and Harvey, 2007). Prospective memory (PM) is a unique form of episodic memory and has been gaining increasing attention due to its theoretical and functional implications (Kliegel et al., 2008). PM by definition is the ability to remember to carry out an intended action in the future (Kliegel et al., 2008). According to the nature of the cue associated with the future intention, three subtypes of PM have been identified (Shum et al., 2004). The event-based PM refers to remembering to execute an intention when an event/cue appears (e.g., remembering to give a document to a colleague when attending the seminar chaired by that colleague). The time-based PM refers to remembering to execute an intention at a specific time or after a period of time (e.g., remembering to turn up for a medical appointment at 3:00 pm on Monday). The activity-based PM refers to remembering to execute an intention after completion of an activity (e.g., remembering to go shopping after finishing homework) (Wang et al., 2010). Moreover, PM can be divided into different phases of cognitive processing, comprising intention formation, intention retention, intention initiation and intention execution (Kliegel et al., 2011). Accordingly, some cognitive resources such as planning, storage, monitoring and switching of inhibition are required during the PM process (Kliegel et al., 2011). The study of PM is both clinically and theoretically important for patients with schizophrenia, for PM has been implicated in many everyday life activities; it is proposed that PM is mostly mediated by the frontal and medial temporal systems (Kliegel et al., 2011 and McDaniel and Einstein, 2011), and dysfunction of the prefrontal cortex and the medial temporal cortex might be especially important for patients with schizophrenia (Antonova et al., 2004 and Minzenberg et al., 2009). Growing evidence has consistently identified PM deficits in schizophrenia patients (Elvevag et al., 2003, Shum et al., 2004, Henry et al., 2007, Altgassen et al., 2008, Chan et al., 2008, Ungvari et al., 2008, Wang et al., 2008a and Wang et al., 2008b). A recent meta-analysis found moderate to large effect sizes for PM deficits in patients with schizophrenia (Wang et al., 2009). Three types of PM were all significantly impaired in schizophrenia, with time-based PM being more impaired than event-based PM. Because it is commonly acknowledged that PM is a complex cognitive function involving multiple processes and cognitive variables, some researchers have tried to elucidate the components of PM impairment in patients with schizophrenia by controlling for other cognitive functions such as working memory, executive function and IQ. The results indicate that PM deficits in schizophrenia patients might be due to the impairment of the cue detection and intention retrieval stage (Woods et al., 2007 and Wang et al., 2008a). Results of some studies also indicate that PM deficits are a primary impairment rather than a secondary consequence of other cognitive impairments (Henry et al., 2007, Woods et al., 2007 and Wang et al., 2008a) whereas other studies found PM deficits to be associated with other cognitive deficits such as impaired retrospective memory (Xiang et al., 2010 and Zhou et al., 2012). However, most of these studies were limited to patients with a long duration of illness and the findings may have been confounded by medication effects and illness duration. There are only two studies identified from the literature that have specifically examined PM performance in patients with first-episode schizophrenia (Lui et al., 2011 and Zhou et al., 2012). Lui et al. (2011) found that patients with first-episode schizophrenia performed poorly in both event-based PM and time-based PM as compared to healthy controls. However, when other cognitive functions were controlled, the significant group difference in time-based PM disappeared and the effect size of event-based PM was reduced from large to moderate. Zhou et al. (2012) replicated a similar finding of PM deficits in patients with first-episode schizophrenia using an ecologically-valid test of PM. Once again, when age, gender, education, and other neurocognitive tests were controlled, the event-based PM and time-based PM differences between groups disappeared. Despite the fact that these two studies recruited first-episode schizophrenia patients, most of their subjects were receiving atypical antipsychotic medication. It is still not clearly known whether PM deficits observed in patients with schizophrenia are the effect of the illness or a result of medication. A recent meta-analysis indicated that PM may have an inverse relationship with antipsychotic medication dosage (Wang et al., 2009). Therefore it is important to rule out the potential medication effect upon PM performance in patients with schizophrenia. This study aimed to clarify these confounding factors by examining a first-episode drug-naïve sample with a relatively short illness duration. In the present study, only event-based PM and time-based PM based on a modified PM paradigm were evaluated. Activity-based PM was not included because a meta-analysis suggested that impairments of time-based PM and event-based PM in schizophrenia have larger mean effect sizes than activity-based PM (Wang et al., 2009). Moreover, the task for activity-based PM is different from the tasks for time-based PM and event-based PM (Wang et al., 2008b, Wang et al., 2009 and Lui et al., 2011). We hypothesized that event-based PM and time-based PM in patients with first-episode psychosis (FEP) are both impaired. We also hypothesized that other cognitive domains, such as working memory, have differential effects on event-based and time-based PM in FEP patients.