Processing speed and working memory span: their differential role in superficial and deep memory processes in schizophrenia

Stability of Verbal Fluency in Outpatients with Schizophrenia

While it is well established that individuals with schizophrenia exhibit a wide range of neurocognitive deficits, there is significant heterogeneity in this regard. Impairments in verbal fluency appear to present consistently across most individuals with the illness. The present study examined the stability of verbal fluency abilities in chronic schizophrenia longitudinally. It was hypothesized that semantic but not phonemic verbal fluency performance would be stable over one year. Data was extracted from a larger study that followed 53 outpatients (70% male; mean age = 39.2 years) diagnosed with schizophrenia or schizoaffective disorder. At each testing interval (baseline, 6, and 12 months), the Brief Assessment of Cognition in Schizophrenia was administered, which included phonemic (i.e., F, S) and semantic (i.e., animals) verbal fluency tasks. No significant differences were found across time points for semantic and phonemic verbal fluency with respect to mean number of words generated, clustering, and switching. The findings provide evidence of stability in semantic and phonemic verbal fluency abilities in chronic schizophrenia. Moving forward, it would be valuable to examine verbal fluency performance longitudinally across multiple stages of illness (i.e., clinically high-risk to chronic schizophrenia).

Decreased processing speed might account for working memory span deficit in schizophrenia, and might mediate the associations between working memory span and clinical symptoms

Objective

Verbal working memory span is decreased in patients with schizophrenia, and this might contribute to impairment in higher cognitive functions as well as to the formation of certain clinical symptoms. Processing speed has been identified as a crucial factor in cognitive efficiency in this population. We tested the hypothesis that decreased processing speed underlies the verbal working memory deficit in patients and mediates the associations between working memory span and clinical symptoms.

Method

Forty-nine schizophrenia inpatients recruited from units for chronic and acute patients, and forty-five healthy participants, were involved in the study. Verbal working memory span was assessed by means of the letter-number span. The Digit Copy test was used to assess motor speed, and the Digit Symbol Substitution Test to assess cognitive speed.

Results

The working memory span was significantly impaired in patients (F(1,90) = 4.6, P < 0.05). However, the group difference was eliminated when either the motor or the cognitive speed measure was controlled (F(1,89) = 0.03, P = 0.86, and F(1,89) = 0.03, P = 0.88). In the patient group, working memory span was significantly correlated with negative symptoms (r = –0.52, P < 0.0001) and thought disorganisation (r = –0.34, P < 0.025) scores. Regression analyses showed that the association with negative symptoms was no longer significant when the motor speed measure was controlled (β = –0.12, P = 0.20), while the association with thought disorganisation was no longer significant when the cognitive speed measure was controlled (β = –0.10, P = 0.26).

Conclusions

Decrement in motor and cognitive speed plays a significant role in both the verbal working memory impairment observed in patients and the associations between verbal working memory impairment and clinical symptoms.

A systematic review on the genetics of male infertility in the era of next-generation sequencing

OBJECTIVES

To identify the role of next-generation sequencing (NGS) in male infertility, as advances in NGS technologies have contributed to the identification of novel genes responsible for a wide variety of human conditions and recently has been applied to male infertility, allowing new genetic factors to be discovered.

MATERIALS AND METHODS

PubMed was searched for combinations of the following terms: 'exome', 'genome', 'panel', 'sequencing', 'whole-exome sequencing', 'whole-genome sequencing', 'next-generation sequencing', 'azoospermia', 'oligospermia', 'asthenospermia', 'teratospermia', 'spermatogenesis', and 'male infertility', to identify studies in which NGS technologies were used to discover variants causing male infertility.

RESULTS

Altogether, 23 studies were found in which the primary mode of variant discovery was an NGS-based technology. These studies were mostly focused on patients with quantitative sperm abnormalities (non-obstructive azoospermia and oligospermia), followed by morphological and motility defects. Combined, these studies uncover variants in 28 genes causing male infertility discovered by NGS methods.

CONCLUSIONS

Male infertility is a condition that is genetically heterogeneous, and therefore remarkably amenable to study by NGS. Although some headway has been made, given the high incidence of this condition despite its detrimental effect on reproductive fitness, there is significant potential for further discoveries.

Memory impairment and the mediating role of task difficulty in patients with schizophrenia

Using meta-analytic methods, we sought to synthesize the research literature on memory impairment in schizophrenia. Additionally, we compared performances across memory measures to determine if task difficulty (e.g., effortful encoding and retrieval vs non-effortful encoding and retrieval) could account for variance across studies. Our primary measures of interest included the California Verbal Learning Test, Wechsler Memory Scale, Rey Auditory Verbal Learning Test, Hopkins Verbal Learning Test, Rey-Osterrieth Complex Figure Test, and the Benton Visual Retention Test. We searched for all studies that met inclusion criteria using PubMed, PsycINFO, Scholars Portal Search, and Google Scholar. Studies were included if: (i) they were published after 1980; (ii) healthy controls were compared to patients with schizophrenia; (iii) at least one of the noted measures of interest was employed in the primary study; and (iv) the primary study included data that could be transformed to point estimate effect sizes (i.e., Cohen's d). Cohen's d was calculated between patients and healthy controls, along with overall 95% confidence intervals. A two-tailed independent samples t-test was conducted to assess if performance differed on various paired subtests of the same domain. Large effect sizes were found for all memory tests. No significant differences were found between subtests. In conclusion, patients with schizophrenia experience significant verbal and visual memory impairments, which are not explained by task difficulty. Patients were unable to learn or retrieve more reliably despite repetition and cuing strategies, suggesting that memory impairment in the illness is not a function of task difficulty.

Schizophrenia and depression: The relation between sleep quality and working memory

Sleep is known to be markedly disturbed in patients with depression, but in patients with schizophrenia these problems are underestimated. This research aimed to determine if a relationship existed between sleep problems in patients with schizophrenia and with depression and their reduced working memory (WM) performance. Thirty outpatients with schizophrenia, 30 outpatients with depression, and 30 healthy control participants were enrolled in this study. All participants completed a sleep questionnaire (i.e., Pittsburgh Sleep Quality Index (PSQI)), two simple WM tasks tapping only its storage component (i.e., digit span forward and backward task), and two complex WM tasks tapping both its storage and processing components (i.e., letter-number sequencing and reading span task). The results showed that neither psychiatric group differed from the healthy controls on simple WM tasks. Patients with schizophrenia did not differ from those with depression in the performance of simple or complex WM tasks. However, patients with schizophrenia, and, to a lesser degree, patients with depression performed significantly worse than the healthy control participants on complex WM tasks, which was visible in lower WM scores for patients with depression and in slower information processing, as well, for patients with schizophrenia. Finally, a significant negative relationship was found between the PSQI score and the reading span task scores; thus, participants with worse performance tended to report more sleep problems. To conclude, sleep needs to receive more priority when treating patients with depression and especially patients with schizophrenia because better sleep improves (working) memory performance and daily functioning.

Cognitive correlates of verbal memory and verbal fluency in schizophrenia, and differential effects of various clinical symptoms between male and female patients

BACKGROUND

Impairment of higher cognitive functions in patients with schizophrenia might stem from perturbation of more basic functions, such as processing speed. Various clinical symptoms might affect cognitive efficiency as well. Notably, previous research has revealed the role of affective symptoms on memory performance in this population, and suggested sex-specific effects.

METHOD

We conducted a post-hoc analysis of an extensive neuropsychological study of 88 patients with schizophrenia. Regression analyses were conducted on verbal memory and verbal fluency data to investigate the contribution of semantic organisation and processing speed to performance. The role of negative and affective symptoms and of attention disorders in verbal memory and verbal fluency was investigated separately in male and female patients.

RESULTS

Semantic clustering contributed to verbal recall, and a measure of reading speed contributed to verbal recall as well as to phonological and semantic fluency. Negative symptoms affected verbal recall and verbal fluency in the male patients, whereas attention disorders affected these abilities in the female patients. Furthermore, depression affected verbal recall in women, whereas anxiety affected it in men.

CONCLUSIONS

These results confirm the association of processing speed with cognitive efficiency in patients with schizophrenia. They also confirm the previously observed sex-specific associations of depression and anxiety with memory performance in these patients, and suggest that negative symptoms and attention disorders likewise are related to cognitive efficiency differently in men and women.