Abstract
Neurodevelopmental motor disorders are highly prevalent conditions affecting the ability to control motor functions. The two most common conditions of this type are developmental coordination disorder (DCD) and chronic tic disorders (CTD). The core impairment in DCD concerns the execution of coordinated voluntary motor actions whilst the core impairment in CTD concerns the lack of control over an excess of involuntary movements. To our knowledge, the specific profiles of motor and cognitive difficulties in DCD and CTD have not been directly or indirectly compared to date. This research gap creates an opportunity for the exploration of typical and atypical motor and cognitive development.
The thesis was guided by the neuroconstructivist framework to explore the profiles of cognitive control processes in DCD and CTD. The term “cognitive control” covered two types of processes believed to be coordinated by the anterior cingulate cortex (ACC): higher-order cognitive control and more mechanistic motor-cognitive control. Based on the current models of the ACC, the presented studies were designed to investigate whether DCD and CTD could be characterised by different patterns of dopaminergic availability and/or hypo-/hyper-activation of the ACC. The methodology used was carefully developed through piloting, adapting and validating the protocols which included electroencephalography (EEG), cognitive tasks and questionnaire-based measures. Following the principles of the neuroconstructivist approach, observed differences in neural and behavioural outcomes were investigated in the context of potential developmental compensation. Outcomes were also directly compared between children and adults to identify atypical developmental trajectories. Lastly, participants’ emotional and behavioural functioning difficulties were investigated as potential direct consequences of developmental motor-cognitive control deficits.
The results show no significant differences between DCD, CTD and control groups in terms of higher-order cognitive control. On the other hand, motor-cognitive control abilities were significantly affected in both DCD and CTD with a significant developmental delay compared to peers in the general population. However, the dominant and persistent profile of specific motor difficulties associated with the low performance was different between the conditions. In addition, adult individuals with DCD performed a higher-order cognitive control task with good accuracy but they had attenuated response-related neural activity. A potential pattern of compensation was found with increased stimulus-related activity to stimuli associated with negative reinforcement. The results suggest possible reduction in dopaminergic activity in DCD. Overall, the findings are consistent with the assumption that ACC might be hypoactive in DCD and hyperactive in CTD. Emotional functioning was also affected in both conditions, and we propose that this occurs due to the interaction between cognitive-emotional regulatory deficits associated with atypical neurodevelopment and environmental factors.