Melbourne School of Psychological Sciences - Theses
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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.