Date of Award

2020

Degree Name

Doctor of Philosophy (College of Health Sciences)

Schools and Centres

Health Sciences

First Supervisor

Doctor Charles Adam Wigley

Second Supervisor

Professor Beth Hands

Abstract

Developmental coordination disorder (DCD) is a neurodevelopmental condition that is characterised by an inability to acquire and execute well-coordinated movements at an age appropriate level (American Psychiatric Association, 2013). Converging evidence suggests that children with DCD experience motor planning difficulties compared to typically developing children; however, these difficulties may be task dependent. To our knowledge, the underlying nature of this deficit as well as the task parameters that might affect motor planning are not well established. Also, while it has been reported that alterations in areas of the frontal and parietal lobe may underlie poor motor planning in this population, little is known about the relationship between motor planning and brain morphology in children with DCD. This thesis was undertaken with the aim to examine motor planning in children with DCD to clarify the nature of motor planning difficulties based on task complexity and examine the relationship between neurological structures and motor planning inefficiency in this population.

To gain an understanding of the nature of motor planning difficulties in children with DCD, two behavioural studies, one neuroimaging and one systematic review and meta-analysis were undertaken. In the first study, boys aged 8 – 12 years with (n = 10) and without DCD (n = 17) completed four grip selection tasks of different levels of complexity. The findings indicated that children with DCD performed significantly poorer compared to their peers on the most complex (octagon) task only. Qualitative evaluation of the ten papers included in the systematic review confirmed that motor planning ability in children with DCD was task dependent with performance differences between children with and without DCD being most evident when tasks were complex. Further, task parameters requirements - the number of grip choices, level of precision, number of movement sequences and the degree of hand rotation, were identified as likely contributing to the complexity of a task. Quantitative analyses revealed that with an increase in grasp choices, movement sequences and precision level, children with DCD performed poorer than typically developing children. In the third study, an examination of the grasping behaviours during the complex octagon task revealed that children with DCD (n = 14) used a less optimal strategy compared to their typically developing peers (n = 18). Interestingly, with instructions to imagine the task prior completion, those with DCD performed similarly to their peers without prior motor imagery instruction. Finally, in the fourth study (N = 20), using Magnetic Resonance Imaging (MRI), decrease in cortical thickness and cortical surface area of the superior parietal lobule was related to an inefficiency in complex motor planning as observed in children with DCD (n = 9).

Taken together, these findings indicate that the observed motor planning inefficiency in children with DCD is not a general deficit but is task-dependent and becomes more apparent when task complexity increases. With an increase in task constraints, significant differences in motor planning ability between those with and without DCD are to be expected. Mental practice of a movement before initiation can improve planning performance in those with DCD. Further, morphological alterations of the superior parietal lobule are related to a lower ability to plan motor actions in children with DCD. Based on the assumption that the efficiency of motor planning is dependent on the ability to anticipate actions, support is provided for the internal modelling deficit hypothesis in children with DCD.

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