Executive function in children and adolescents with Down Syndrome: a systematic review and Kuwait-based intervention

Abstract

Individuals with Down syndrome (DS) have been found to exhibit significant atypicalities in most executive functions (EFs), such as working memory (WM), cognitive flexibility/shifting, inhibition, self-regulation and attention. However, to date there has been limited research into the relative strengths and weaknesses in their EF profiles. Moreover, EFs in DS have received very little attention in the Kuwaiti research context, despite the need for greater support and resources for those with DS in non-Western countries. There is broad agreement in the research literature, however, that WM is one of the more affected EFs in children and adolescents with DS. This thesis therefore set out to investigate EF profiles in, and WM support for, children and adolescents with DS, through two interlinked studies. Study 1 was a systematic review of EF research in DS. Relevant databases were searched for studies that were published prior to January 2020, involving children and adolescents with DS, comparing their EFs with various comparison populations. Fifty-five studies were included in the final review. The results revealed that, in general, all EFs are atypically developed in individuals with DS. WM appeared to be the most challenged EF, particularly verbal (though not necessarily visuospatial) WM, and emotional control appeared to be the least atypical, relative to controls. Furthermore, there are significantly fewer studies focusing solely on adolescents than on children or mixed-age samples, and even fewer that compare the EF performance of children and adolescents. There are also no studies that draw comparisons between different tools measuring the same EF in the same samples, to ascertain whether different results are gained from different measures. Finally, studies use a variety of comparison approaches, including mental age and chronological age matching, or normative data. They also involve a range of different comparison groups, allowing only tentative conclusions to be drawn from current research. In study 2 an intervention that aimed to support teachers in Kuwait to use different strategies in the classroom that could encourage the development of WM in children and adolescents with DS, was devised, conducted and evaluated. The aim of this study was to explore the effectiveness of the WM intervention on teachers‘ knowledge surrounding WM, their use of WM strategies in the classroom and on cognitive, behavioural, and academic outcomes for children and adolescents with DS. Study 2 involved 31 children and adolescents with DS (aged 7 to 16 years) and 28 literacy and numeracy teachers from specialist units in 4 mainstream primaries schools. The study adopted a quasi-experimental design, involving 2 groups of teachers: an experimental group (enrolled on the WM intervention) and an active control group (enrolled on a positive behaviour support intervention). Outcomes were assessed using a range of measures to test EF, WM, and challenging and social behaviour. Teachers‘ knowledge of WM was also evaluated to examine the effectiveness of the intervention, and the experimental group was also observed to explore any difference on their use of WM strategies, pre- and post intervention. Teachers‘ perspectives on the feasibility and acceptability of the intervention process were also gathered, using focus groups. Results showed that the WM in the experimental group significantly improved from pre-intervention to follow-up compared to the control group. In contrast, the control group had significantly lower incidence of challenging behaviour and an increase in prosocial behaviour compared to the experimental group at follow-up. There was no significant difference on academic achievement in literacy and numeracy outcomes between the two groups at follow-up. Moreover, teachers‘ knowledge about WM was found to improve significantly in the experimental group compared to the control group, and the use of WM strategies significantly improved from pre- to post-intervention in the experimental group. Overall, the systematic review in study 1 provides a novel contribution to understanding EFs in the DS population, revealing that WM is the EF that those with DS struggle with the most. These findings indicate the necessity of effective interventions to address and improve this EF in children and adolescents with DS. Furthermore, the systematic review revealed significant gaps in current understanding and research knowledge of executive functioning more generally in DS: for example, a need for further studies focusing solely on WM functioning in groups of children and adolescents with DS, especially studies that compare a range of measures to test WM functioning. Moreover, the relative strengths of emotional control in those with DS should be further explored. The findings from study 2 established the effectiveness of the WM intervention aimed at teachers - a novel approach in Kuwait - in the short-term, although the long-term efficacy of the intervention is unknown. Therefore, it would be beneficial to conduct a longer-term follow-up assessment in the future. Additionally, it may be helpful in future studies to conduct an intervention to improve WM at home, so there is a consistency of approach between home and school. The results of these studies therefore have practical implications for teachers, given the finding that when teachers employ strategies to boost WM, the WM functioning of children and adolescents with DS is improved. Helping teachers to become experts in a range of EF support strategies may also lead them to interact differently with children and adolescents with DS, which could improve students‘ abilities in other areas (such as other cognitive function or social behaviour). Importantly, the study also altered teachers‘ understanding of, and attitudes towards, the learning capabilities of individuals with DS, with important implications for reducing cognitive difficulties in children with DS in Kuwait.