Melbourne School of Psychological Sciences - Theses
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ItemPragmatic language and theory of mind in children with symptoms of ADHD: relationships with executive functions( 2018)Children’s social, academic and interpersonal functioning is sustained by language in use, yet a moderate body of research indicates that children with ADHD, and children with ADHD symptoms, have problems with pragmatic language. They can be prone to excessive talking, poor conversational turn-taking and lack of clarity and coherence in their utterances. Pragmatic language is thought to depend in part on theory of mind (ToM) and on executive functions such as sustained attention and response inhibition. This research first investigates the nature and extent of pragmatic language problems in children with symptoms of ADHD, and any co-occurring problems with ToM. In view of neurocognitive heterogeneity in children with ADHD and in the general population, the research then examines whether pragmatic language problems are related to specific subgroups of executive function, and whether any ToM difficulties are similarly related. A community sample of 148 children aged 8 to 10 years participated (76 boys). ADHD symptoms and pragmatic language ability were assessed by parent questionnaire. Most of the children (n = 110, 57 boys) then completed the Sustained Attention to Response Task (SART; Robertson, Manly, Andrade, Baddeley, & Yiend, 1997) and a digit span task, while conversational pragmatics was assessed using observational ratings from a semi-structured conversation and ToM was assessed from children’s responses to an animated triangles task. Children with ADHD symptoms (n = 29) showed substantially poorer pragmatic language than children without such symptoms (n = 81), in terms of both parent report of communications skills and conversational pragmatics. They evinced subtle problems with ToM. Cluster analysis revealed three distinct profiles of performance on the SART, with one subgroup characterised by poor sustained attention (n = 13), one subgroup with poor response inhibition (n = 16) and the remainder with no particular weakness (n = 81). Children with ADHD symptoms were distributed across all three subgroups. Nonetheless, the subgroup with poor sustained attention had a higher level of ADHD symptoms and a consistent pattern of poorer conversational pragmatics and ToM than the subgroup that performed well on the SART. Surprisingly, the subgroup with poor response inhibition did not show poorer pragmatic language or ToM, nor higher level of ADHD symptoms, than the subgroup that performed well on the SART. The results indicate that neurocognitive heterogeneity amongst children with ADHD symptoms is nested within heterogeneity in the general population. Moreover, specific weakness in sustained attention may contribute to behavioural symptoms of ADHD and to problems with pragmatic language and ToM amongst a subgroup of school-aged children. Sustained attention may be required to monitor the communicative intentions of conversational partners and the content, timing and relevance of conversational turns. Executive weakness, however, does not appear to underlie ADHD symptoms or pragmatic language and ToM problems in all children, posing a challenge to causal models of ADHD. Results are discussed in terms of whether behavioural symptoms of ADHD might disrupt both interpersonal engagement and the application of executive functions in communicative contexts.
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ItemThe relationships between response time variability, brain signals, ADHD symptoms, and behavioural control( 2018)Individuals with Attention Deficit Hyperactivity Disorder (ADHD) often produce greater response time variability (RTV) when performing cognitive tasks. It is still unclear why increased RTV is observed in ADHD. One possible explanation for this is that individuals with ADHD may have aberrant patterns of brain connectivity, leading to inefficient communication between brain regions. Graph theoretical analysis is an approach used to characterise patterns of brain connectivity. This study aimed to investigate the relationship between brain connectivity, RTV, age, and levels of ADHD symptoms using a cross sectional design. Children aged 9-12 years and adolescents aged 15-18 years performed three tasks in this thesis - the Sustained Attention to Response Task (SART), the Flanker SART, and the Detection of Disappearance Task (DDT). EEG was recorded while participants performed the three tasks. The Conners 3 questionnaire was used to measure the participants' levels of ADHD symptoms. Multiple parameters were computed to reflect different aspects of RTV, using ex-Gaussian and the Fast Fourier Transform (FFT) techniques. Tau from the ex-Gaussian analysis reflects skewness and sigma reflects deviation of the Gaussian portion of the RT distribution. The FFT analysis allows an examination of periodic changes in RT, with moment-to-moment variability (Fast Frequency Area Under the Spectra, FFAUS) and slow changes in RT (Slow Frequency Area Under the Spectra, SFAUS) computed. The ex-Gaussian analysis was performed in all three studies, and the FFT analysis was performed in the SART and Flanker SART. From the EEG recording, functional connectivity between 64 electrodes was examined, and global efficiency and modularity were computed, reflecting functional integration and segregation of the brain respectively. There was a positive association between tau and levels of ADHD symptoms in all three studies, but sigma showed no significant association in any of the studies. This finding suggests that higher levels of ADHD symptoms are associated more occurrences of attentional lapses and greater RTV. FFAUS was positively associated with levels of ADHD symptoms in both the SART and Flanker SART, suggesting that individuals with higher levels of ADHD symptoms show difficulty with sustained attention. SFAUS was positively associated with levels of ADHD symptoms only in the SART. Greater task complexity presented by flankers might help to increase arousal levels for those with more pronounced levels of ADHD symptoms. Adolescents demonstrated lower RTV than the children in all RTV measures, indicating stability of performance increases from late childhood to late adolescence. The graph analysis of EEG functional connectivity showed that lower RTV was associated with more integrated brain network functioning, as measured by global efficiency. This supports the view that stable responses are achieved through more integrated brain functioning. More integrated brains may allow for more efficient transfer of information resulting in more stable responses. Adolescents showed greater levels of integration and lower levels of segregation of the brain during performance, suggesting that the brain might be becoming more integrated and less segregated from late childhood to late adolescence.
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ItemDiffusion weighted imaging analysis of children with attention deficit hyperactivity disorder and language problems( 2017)BACKGROUND: Research indicates that children with Attention Deficit Hyperactivity Disorder (ADHD) have three times the risk of co-occurring language problems (LP) compared to typically developing children (Sciberras et al, 2014). The specific types and magnitude of these LP, and neurobiology underlying the co-occurrence remains unclear. OBJECTIVES: a) to establish empirically derived data on the types and effect size of LP seen in children with ADHD compared to controls; and b) to characterise white matter microstructural differences in the dorsal and ventral language networks of children with ADHD (with and without LP), children with LP alone, and non-ADHD controls. METHOD: For Part a) of this study, a systematic review and meta-analyses were conducted according to PRISMA guidelines and rigorously defined inclusion criteria. For Part b) of this study, 163 children (9–11 years) received structural T1 and diffusion magnetic resonance imaging (63: ADHD, 76: Controls met diagnostic criteria). LP were identified using a standardised measure of language ability. High angular resolution diffusion imaging and whole brain tractography were generated using constrained spherical deconvolution. Dorsal and ventral language tracts were defined using include/exclude regions-of-interest on a cohort-specific template. Tract diffusion parameters were compared across groups via linear regression covarying for age, sex, and respective whole brain diffusion parameters. The model was then re-analysed with the addition of an inattention covariate. RESULTS: The review of previous literature for Part a) found evidence of overall, expressive, receptive and pragmatic LP in children with ADHD across the 21 included studies (Hedges g: .98–1.23; ADHD: 1,209; Control: 1,101). While children with ADHD+LP and those with LP alone performed equally poor on a measure of language function, Part b) neuroimaging analysis revealed significant differences in the white matter microstructure of dorsal and ventral language tracts between the groups, and specific aberrations unique to children with LP alone and ADHD+LP respectively. Children with LP alone were right lateralised in their dorsal language stream compared to all other groups. White matter abnormalities in the ventral tracts (the left uncinate fasciculus in particular) were unique to children with ADHD+LP compared to other groups. Finally, dorsal white matter tracts no longer showed a significant association with language ability when inattention was accounted for in the model. DISCUSSION: Part a) of this study provides the first empirical data to demonstrate large and consistent deficits in specific domains of language for children with ADHD. Part b) neuroimaging findings of white matter abnormalities in the language network may account for such language deficits. The results indicate that different neural origins may underlie the development of LP in isolation, compared to co-occurring ADHD and LP. The results further suggest that in some cases, the abnormal white matter tracts are influenced by factors other than language performance, such as inattentive factors. The findings support a need to examine children presenting with ADHD for potentially co-occurring LP so that they do not go undetected and untreated. It is possible that certain LP seen in ADHD are the result of inattention, which has a secondary negative effect on performance on a language measure. To this end, interventions utilising a combination of attention-based and traditional language-based speech-pathology services for these children may be a fruitful area for further investigation.