A Novel Framework to Measure Executive Function in Down Syndrome With Applications for Early Clinical Diagnosis of Dementia

Same same but different: Subtle but consequential differences between two measures to linearly integrate speed and accuracy (LISAS vs. BIS)

Condition-specific speed-accuracy trade-offs (SATs) are a pervasive issue in experimental psychology, because they sometimes render impossible an unambiguous interpretation of experimental effects on either mean response times (mean RT) or percentage of correct responses (PC). For between-participants designs, we have recently validated a measure (Balanced Integration Score, BIS) that integrates standardized mean RT and standardized PC and thereby controls for cross-group variation in SAT. Another related measure (Linear Integrated Speed-Accuracy Score, LISAS) did not fulfill this specific purpose in our previous simulation study. Given the widespread and seemingly interchangeable use of the two measures, we here illustrate the crucial differences between LISAS and BIS related to their respective choice of standardization variance. We also disconfirm the recently articulated hypothesis that the differences in the behavior of the two combined performance measures observed in our previous simulation study were due to our choice of a between-participants design and we demonstrate why a previous attempt to validate BIS (and LISAS) for within-participants designs has failed, pointing out several consequential issues in the respective simulations and analyses. In sum, the present study clarifies the differences between LISAS and BIS, demonstrates that the choice of the variance used for standardization is crucial, provides further guidance on the calculation and use of BIS, and refutes the claim that BIS is not useful for attenuating condition-specific SATs in within-participants designs.

A meta-analysis of the executive function components inhibition, shifting, and attention in intellectual disabilities

BACKGROUND

Executive function is a concept for higher-order cognitive functions, which have the role of controller and modulator of cognitive abilities. The consensus in the literature is that people with an intellectual disability perform significantly lower on executive function tasks than groups matched on chronological age. The comparison with groups matched on mental age is less clear. Therefore, the objective of this meta-analysis was to investigate to what extent executive function is impaired in people with intellectual disability compared with a typically developing control group matched on mental age. It was also investigated if the executive function component and intellectual disability aetiology moderated the effect.

METHODS

Eligibility criteria were participants with intellectual disability (IQ ≤ 75) without a dual diagnosis; a comparison group matched on mental age; executive function outcome reported in a group comparison study design with n ≥ 10. Working memory tasks and ratings of executive function were not included. The literature search yielded 6637 potentially interesting articles. Twenty-six studies (with 99 effect sizes) including 1395 participants were included in the quantitative synthesis.

RESULTS

A multilevel random-effects meta-analysis found that people with intellectual disability performed statistically significantly lower than the mental age-matched group on the executive function tasks, g = -0.34, 95% confidence interval = [-0.53, -0.16]. However, the heterogeneity between effect sizes was large. The intellectual disability aetiology moderator was significant, but it only reduced the heterogeneity marginally.

CONCLUSION

The overall conclusion is that individuals with an intellectual disability have more problems with executive function tasks than mental age-matched controls. Limitations are the large unexplained variance and the remarkably high number (69) of different tests that were used, which make more detailed conclusions problematic. This meta-analysis implies that future studies need to be of better quality, to have higher power, and to a higher degree use the same executive function tests.

Inhibitory Abilities in Individuals with Down Syndrome: Investigation of Interference Suppression Using an Adapted Version of Navon Task

Only a few studies have investigated inhibitory sub-components in individuals with Down syndrome (DS). This study investigates interference suppression, through global-local processes, in 50 people with DS matched for mental age (MA) with 63 typically developing children (MA = 23.6 and 6.8 years respectively). We adapted and administered a non-verbal Navon-shape task with high-familiarity symbols. For both groups, results showed equal performance on global vs. local items in the congruent condition, whereas significantly better performance on global conditions when faced with incongruent items. A greater impairment in incongruent responses emerged for both groups and more so for individuals with DS.

Inhibitory Dimensions and Delay of Gratification: A Comparative Study on Individuals with Down Syndrome and Typically Developing Children

While previous research on inhibition in people with Down syndrome (DS) reported contradictory results, with no explicit theoretical model, on the other hand, a more homogeneous impaired profile on the delay of gratification skills emerged. The main goal of the present study was to investigate response inhibition, interference suppression, and delay of gratification in 51 individuals with DS matched for a measure of mental age (MA) with 71 typically developing (TD) children. Moreover, we cross-sectionally explored the strengths and weaknesses of these components in children and adolescents vs. adults with DS with the same MA. A battery of laboratory tasks tapping on inhibitory sub-components and delay of gratification was administrated. Results indicated that individuals with DS showed an overall worse performance compared to TD children on response inhibition and delay of gratification, while no differences emerged between the two samples on the interference suppression. Additionally, our results suggested that older individuals with DS outperformed the younger ones both in response inhibition and in the delay of gratification, whereas the interference suppression still remains impaired in adulthood. This study highlights the importance of evaluating inhibitory sub-components considering both MA and chronological age in order to promote more effective and evidence-based training for this population.

Down syndrome and dementia: advances in the field

PURPOSE OF REVIEW

People with Down syndrome represent the world's largest population with a genetic risk for Alzheimer's disease. This review will provide a short summary of what is known and will include recent findings from the field.

RECENT FINDINGS

There has been an increasing focus on biomarker research in this population, with a number of studies presenting findings on promising new markers - Neurofilament Light (NfL) appears to be one such promising marker that has emerged. Imaging studies have increased our knowledge on the progression of Alzheimer's disease in this population.

SUMMARY

The inclusion of people with Down syndrome in dementia research is vital from a scientific and an equity perspective. Recent advances in the field can have further impact with multisite, cross country collaborative efforts. For this to happen, instruments need to be validated across language and cultures.