All the subtypes of prospective memory, particularly time-based prospective memory, are significantly impaired in patients with schizophrenia, according to a study published in Schizophrenia Research.
Prospective memory (PM) impairment, defined as the failure to remember to perform something in the future, has been gaining increasing attention in schizophrenia research. This meta-analysis included 29 English- and Chinese-language case-control studies of PM in schizophrenia found through searching the Chinese Biomedical, China Journal Net databases, Cochrane Library, EMBASE, PsycINFO, PubMed, and WanFang databases from their inception until August 14, 2017. Random-effects models were used to calculate standardized mean differences (SMD) and their 95% confidence intervals (CI).
The 29 included case-control studies (n=2492, mean age 21.8 to 67.5 years, 36.8% to 100% men [in the 26 studies with available data], and 10.2 to 13.7 mean years of education [in the 23 studies with available data]) compared the overall and 3 subtypes of PM in patients with schizophrenia (n=1284) with healthy controls (n=1208). The Newcastle-Ottawa Scale (NOS) total score for the studies ranged from 5 to 8, with 23 rating as “high quality” (NOS ≥7).
Schizophrenia participants showed significantly poorer overall PM compared with healthy controls, with a large effect size (n=1044; SMD -1.125; 95% CI, -1.461 to -0.789; P <.001; I²=83%). In subgroup analyses, significant differences were found in overall PM between eco-valid and dual-task laboratory measurements (SMD -1.542 vs -0.725), higher predominance of men and no sex predominance (SMD -1.679 vs -0.800), chronic and first-episode patients (SMD -1.237 vs. -0.641), lower and higher education levels (SMD -1.373 vs.-0.637), and older and younger patients (SMD -1.398 vs. -0.763).
The meta-analysis of time-based PM showed impairment with a large effect size in schizophrenia participants compared with healthy controls (n=1632; SMD -1.155; 95% CI, -1.329 to -0.980; P <.001; I²=60%). The meta-analysis of event-based PM showed significantly more severe impairment in schizophrenia participants compared with healthy controls (n=2042; SMD -1.068; 95% CI, -1.346 to -0.790; P <.001; I²=88%). The meta-analysis of activity-based PM showed significant impairment in schizophrenia participants compared with healthy controls (n=401; SMD -0.563; 95% CI, -0.849 to -0.278; P =.0001; I²=50%). In addition, “Chronic patients will have more severe PM impairment compared to first-episode patients, as chronic patients have more gray matter loss in the prefrontal cortex.”
Limitations include the heterogeneous sample characteristics, settings, and illness phases of the studies included, and the fact that measures of prospective memory differed between the studies. Assessing forgetfulness as an impairment in schizophrenia, study investigators conclude, “in this meta-analysis overall PM and all its subtypes… were significantly impaired in schizophrenia. Chronic illness stage, more severe negative symptoms, and eco-valid PM measurements were significantly associated with more severe PM impairment. More high-quality studies with large sample sizes are needed to confirm these findings.”
Zhou FC, Zheng W, Lu L, et al. Prospective memory in schizophrenia: a meta-analysis of comparative studies [published online August 22, 2019]. Schizophr Res. doi: 10.1016/j.schres.2019.08.010