Investigating working memory impairments in individuals with autism spectrum disorder

Habib, Abdullah (2019) Investigating working memory impairments in individuals with autism spectrum disorder. PhD thesis, University of Glasgow.

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Autism spectrum disorders (ASD) are lifelong neurodevelopmental disorders characterized by communication difficulties, social impairment and fixated interests along with repetitive behaviours. Although neuropsychological impairments are not part of diagnostic criteria, many people with ASD experience significant cognitive impairments. Executive function deficits are commonly experienced by individuals with ASD, and WM which plays an important role in human cognition and a central role in executive function has been reported to be impaired in individuals with ASD. Studies examining whether individuals with ASD experience significant WM impairments have produced inconsistent findings thus it is not clear whether WM deficits are commonly experienced by individuals with ASD. Therefore, Chapter 2 investigated whether individuals with ASD experience significant impairments in WM and whether there are specific domains of working memory that are impaired while controlling for age and IQ as potential moderators. The findings of this chapter indicate that across the lifespan, individuals with ASD demonstrate large impairments in WM across both phonological and visuospatial WM domains when compared to healthy individuals.

The importance and role of working memory to everyday tasks is well established, but research has yet to investigate if the WM deficiencies reported on cognitive tasks are translated to difficulties with everyday life. To investigate this question, Chapter 4 explored whether individuals with ASD experience significant everyday WM related difficulties and if they are everyday concern of adults with ASD. 111 males with ASD between the ages of 18 and 35 who were recruited through the National Health Service Greater Glasgow and Clyde, completed the WMQ, a self-assessment questionnaire. This finding reveals that individuals with high functioning autism display significant impairment in WM related difficulties in everyday life.

It is evident from Chapter 3 and 4, that WM deficiencies is a definite problem in individuals with ASD. With WM impairments being present in multiple psychiatric disorders, there has been urgent need for effective treatment options. While both pharmacological and non-pharmacological approaches have shown positive results, both are far from leading to a significant improvement in WM in patients with ASD. In the last 15 years, there has been a growing interest in the use of non-invasive brain stimulation methods such as transcranial direct current stimulation (tDCS) as a way of improving WM in typically developed individuals and in clinical populations. In chapter 5 a phase II trial was conducted to evaluate the adverse effects of tDCS and investigate whether anodal tDCS lead to an improvement in working memory accuracy scores when administered over the left DLPFC when compared to sham in adults with high functioning autism. Additionally, we investigated whether the observed effect of tDCS over the left DLPFC and working memory scores is dependent on polarity anodal (positive) versus cathodal (negative) stimulation). A random sample of 50 male participants consisting of 25 individuals with HFA and 25 typical developed (TD), between the ages of 18-35 with a mean age of 24.33 (SD=3.80) took part in this study. All self-reported that they had normal or corrected vision, normal colour vision and passed the tDCS safety screening process. Participants underwent three experimental conditions: anodal, cathodal and sham stimulation. One session involved anodal stimulation over the DLPFC (F3) with the cathode placed over the contralateral supraorbital area. The next session involved the same protocol but the cathode electrode was placed over the DLPFC and the anode over the contralateral supraorbital area. The third and final session involved sham stimulation where the current was ‘ramped-up’ for 30 seconds and then ramped down to 0 milliamps over 30 seconds. Participants performed the 3-back working memory task pre, during and post stimulation; tDCS was then applied at a current of 1.5 milliamps for 15 minutes. The findings of this study demonstrated that anodal tDCS for 15 minutes at an intensity of 1.5 mA led to an improvement in WM performance scores when administered over the left DLPFC when compared to baseline, cathodal and sham stimulation of the same area in adults with HFA.

The results of this thesis provide evidence of significantly impaired WM in the literature and everyday life in individuals with ASD. Moreover, it also provides evidence for the possible therapeutic application of tDCS for WM impairments.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: R Medicine > R Medicine (General)
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Health & Wellbeing > Mental Health and Wellbeing
Supervisor's Name: Melville, Professor Craig and Pollick, Professor Frank
Date of Award: 2019
Depositing User: Mr Abdullah Habib
Unique ID: glathesis:2019-76746
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Dec 2019 15:00
Last Modified: 26 Jul 2022 08:54
Thesis DOI: 10.5525/gla.thesis.76746
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