Review
Prospective memory in schizophrenia: A review

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Abstract

The wide range of psychological and cognitive symptoms associated with schizophrenia can often affect the level of independence that individuals with schizophrenia can achieve in their lives. Prospective memory (PM), or memory associated with future intentions, has been proposed as a useful indicator of select independent living skills. Currently, there is limited research with regards to prospective memory in schizophrenia. The current review systematically summarizes the literature focusing on prospective memory in schizophrenia and concludes that individuals with schizophrenia exhibited both an impairment in PM when compared to healthy controls and a general lack of awareness regarding these deficits. The existing research also suggests that PM deficits are not related to chronicity of illness or medications associated with schizophrenia. Limited findings suggest that PM deficits in individuals with schizophrenia may be associated with the ability to live independently and instrumental activities of daily living.

Introduction

Schizophrenia and the vast range of cognitive deficits that accompany the disorder have been extensively studied dating back over a century (Hill, 1900). Despite the ongoing research surrounding schizophrenia and the etiology of the disorder, the predicted course of the disease for each individual remains largely unknown. Treating individuals with schizophrenia remains primarily reactionary and generally deals with acute issues rather than focusing on long-term planning with an emphasis on promoting quality of life and independence. A facet of treatment planning for individuals with schizophrenia that has gained increasing interest over the past few decades is not only assessing basic cognitive functioning but also assessing functional impairment or impairment in everyday living (Sbordone and Long, 1996, Bowie et al., 2010). One type of cognitive processing that is thought to play a role in one's quality of life is their ability to remember to perform tasks in the future, also termed prospective memory (PM). Sub-types of PM discussed in the current review are event-based PM, in which memory to perform an action is cued by an external cue, time-based PM that refers to memory to perform an action at a specified time, and activity-based PM in which memory to perform an action is cued by one's own action. PM, in general, is thought to play a critical role in one's ability to engage in self-maintenance and safe, effective interaction with the world (Guynn et al., 1998).

An asset of many PM tasks is the perceived high ecological validity, often due to the simplicity of the procedures used to examine the cognitive process. For example, study participants are typically asked to simply maintain a future task that needs to be addressed in their memory while engaging in an ongoing task (Einstein et al., 1995). These relatively simple tasks are thought to mirror the unpredictable distractions which arise in the real world and the act of remembering to perform a task at a certain time with only internal cues. In a recent study that examined the effects of PM on medication management ability it was found that performance on laboratory measures of PM often correlate significantly with adherence to medication regimens (Lam et al., 2013). The findings of Lam et al. (2013) are indicative of the high ecological validity of PM tasks. Additionally, the research indicates a direct link between lower PM functioning and poorer adherence to medication schedules.

Detriments in PM across various populations are often believed to present a threat to an individual's independence, safety, and health. In studies assessing older adults' performances on what might be considered a relatively simple PM task (minimal delays between intent to act and execution) it has been found that even the shortest delays between intention formation and execution can cause disruptions in PM (Einstein et al., 2000). As the authors point out, one may easily remember to take their medication while they are in the bedroom, but unless they are able to keep that PM activated sufficiently, they may not be able to execute it when they arrive in the kitchen. Given that a crucial component of treatment for some individuals with chronic mental illness or neurodegenerative disorders is that medications need to be taken at assigned times, a detriment to certain types of PM would likely affect his/her ability to safely live independently.

While memory deficits in schizophrenia have been well-documented (Saykin et al., 1991, Tamlyn et al., 1992, Nathaniel-James et al., 1996, Guillem et al., 2001) there is no clear profile regarding what types of memory deficits appear to be most problematic for this population, or whether retrospective memory (RM) or PM is more beneficial in terms of predicting one's ability to function independently and successfully in everyday tasks. A better understanding of memory processes in schizophrenia is needed, and particularly a better understanding of memory skills needed for successful everyday living. PM may be of particular interest in this population, given that PM, more than traditional RM tasks, “overlaps with other areas of psychology not usually regarded as being about memory” (p. 349) (Winogard, 1988). Specifically, he adds that PM “is part of ongoing action and such factors as attention, motivation, compliance, vigilance, reward, conflicting goals, and the like are all involved” (p. 350) (Winogard, 1988, Graff and Uttl, 2001). Given that PM is viewed as involving supporting cognitive processes that appear to be unique to PM compared to retrospective memory, it is likely that deficits in these supporting areas (e.g. attention, motivation, vigilance) that have been documented in schizophrenia would lead to greater impairments in this population on PM tasks compared to RM tasks and would be associated with greater impairments in individuals with schizophrenia compared to healthy controls or populations who are not characterized by these deficits (Carter et al., 2010, Hahn et al., 2012, Fervaha et al., 2013). In addition, beyond the previously discussed cognitive factors that likely negatively affect PM performance in schizophrenia, there are questions regarding whether time processing or one's internal clock may also be dysfunctional in individuals with schizophrenia (Davalos et al., 2011, Papageorgioua et al., 2013). Given the specific requirements of time-based PM to rely on one's internal clock, it is expected that time-based PM may be the most negatively affected subtype of PM in individuals with schizophrenia.

The first question, therefore, is whether individuals with schizophrenia exhibit PM deficits across studies and across PM paradigms or whether there appear to be certain types of PM tasks that are more problematic for this population. Understanding PM performance in individuals with schizophrenia may allow us to develop a more complete view of both how memory works and how it is impaired in schizophrenia. In addition, a better understanding of PM functioning in schizophrenia could also direct how treatment should be structured and allow those who treat and interact with individuals with schizophrenia to have more realistic expectations in terms of the demands they place on these individuals regarding remembering future events.

Investigation into PM deficits in individuals with schizophrenia to date has suggested a general impairment in this population; however, the subject is relatively new and is lacking a basis of information on which to expand. The current review will explore the research and findings on PM and schizophrenia to try to determine whether deficits are observed across studies and to better understand the types of PM deficits which characterize this population.

Section snippets

Methods

We conducted a combined search of the PsychInfo, MedLine, and PubMed data-bases (through February 2013) using the terms: schizophrenia and PM (88). We limited the search by only including studies written in English (3 excluded) in peer-reviewed journals (2 excluded) that involved human populations (0 excluded) and that included participants diagnosed with schizophrenia (3 excluded). One study did not include specific diagnoses of participants who were termed psychotic and was excluded based on

Results

The number of well-controlled studies that examine the effects of PM on individuals with schizophrenia is relatively small. In an attempt to organize the current literature to highlight the findings and to better understand the nature of PM deficits in schizophrenia, studies are first presented in terms of population differences (e.g. individuals with schizophrenia compared to healthy controls or individuals with schizophrenia compared to clinical populations of interest) followed by a review

Discussion

Deficits in time-, event-, and activity-based PM as well as habitual PM have been demonstrated to be prevalent in patients with schizophrenia when compared with healthy controls and other populations with shared symptoms. Not only do patients with schizophrenia generally appear to show greater impairment on PM tasks, but they also exhibit a general lack of awareness of their deficit and even a lack of memory for whether or not they engaged in the PM task activity. The combination of PM deficits

Role of funding source

Colorado State University provided the databases for data collection for this manuscript. Authors had full access to the data in the study and had full responsibility for the decision to submit for publication.

Contributors

Deana Davalos designed the study and wrote the protocol. Greg Ordemann managed the literature searches and analyses. Deana Davalos, Greg Ordemann, and Jamie Opper undertook the statistical analysis, and Greg Ordemann wrote the first draft of the manuscript. All authors contributed to and have approved the final manuscript.

Conflict of interest

None of the authors have any actual or potential conflict of interests that could inappropriately influence, or be perceived to influence the current work.

Acknowledgments

We would like to thank Colorado State University for access to the institution's abundant resources.

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