Preserved Intention Maintenance and Impaired Execution of Prospective Memory Responses in Schizophrenia: Evidence from an Event-based Prospective Memory Study

Abstract

Executive system dysfunction and impaired prospective memory (PM) are widely documented in schizophrenia. However, it is not yet clarified which components of PM function are impaired in this disorder. Two plausible target components are the maintenance of delayed intentions and the execution of PM responses. Furthermore, it is debated whether the impaired performance on frequently used executive tasks is associated with deficit in PM functions. The aim of our study was twofold. First, we aimed to investigate the specific processes involved in event-based PM function, mainly focusing on difference between maintenance of intention and execution of PM responses. Second, we aimed to unfold the possible connections between executive functions, clinical symptoms, and PM performance. An event-based PM paradigm was applied with three main conditions: baseline (with no expectation of PM stimuli, and without PM stimuli), expectation condition (participants were told that PM stimuli might occur, though none actually did), and execution condition (participants were told that PM stimuli might occur, and PM stimuli did occur). This procedure allowed us to separately investigate performances associated with intention maintenance and execution of PM responses. We assessed working memory and set-shifting executive functions by memory span tasks and by the Wisconsin Card Sorting Test (WCST), respectively. Twenty patients diagnosed with schizophrenia and 20 healthy control subjects (matched according to age and education) took part in the study. It was hypothesized that patients would manifest different levels of performance in the expectation and execution conditions of the PM task. Our results confirmed that the difference between baseline performance and performance in the execution condition (execution cost) was significantly larger for participants diagnosed with schizophrenia in comparison with matched healthy control group. However, this difference was not observed in the expectation condition. The PM performance in the execution condition was correlated with impaired executive functions in schizophrenia. Specifically, the size of execution cost positively correlated with percent of perseverative errors committed on WCST by the patient group. Our results suggest that maintenance of delayed intentions is unimpaired in schizophrenia, whereas the impairment in execution of PM responses is associated with set-shifting deficit.

Neural correlates of the effect of implementation intention on prospective memory

“…In the PM execution phase, the typical instruction group showed stronger activation in the precentral gyrus (BA 6) and middle frontal gyrus (BA 8) than the implementation intention group. The precentral gyrus (BA 6) is located close to the pre‐supplementary motor area (pre‐SMA) and the supplementary motor area (Demeter et al, ) and it functions together with somatosensory areas to implement the PM actions. So, in this phase the PM intention transferred from an abstract level to a concrete and action‐related level (Cona et al, ).…”

Schizophrenia and prospective memory impairments: a review

“…Compared to event-based PM, deficit in time-based PM persisted. Demeter et al, 2016 Chronic schizophrenia patients (n=20) and matched healthy controls (n=20)…”

“…Since these two reviews, a number of studies that examined PM impairments in individuals with schizophrenia have been published. Three studies Au et al, 2016;Demeter et al, 2016) found severe PM impairments in individuals with chronic schizophrenia. Three studies (Cheung et al, 2015;Liu et al, 2017;Lui et al, 2015) showed that first-episode and even first-episode medication-naïve individuals with schizophrenia demonstrated PM impairments.…”

<p>Prospective memory in non-psychotic first-degree relatives of patients with schizophrenia: a meta-analysis</p>

“…There are a number of endophenotypes, and cognitive endophenotypes have been extensively studied. So far, some research has shown that the impairment of PM exists within schizophrenia patients, regardless of chronic,47,60–63 first-episode, or even first-episode drug-naive status,64–66 and meta-analyses and systematic reviews have been conducted 49,67. In this study, it was found that the non-psychotic first-degree relatives of patients with schizophrenia had defects in their prospective memory.…”