Specialization of the motor system in typically developing infants and infants with Down syndrome

• Main Author: Kyjonkova, Hana
• Published: Goldsmiths College (University of London) 2017
• Subjects: 618.92
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.716980

A growing body of evidence suggests that, compared to later in development, the infant brain starts out less specialized, producing more widespread activation in response to stimuli. Such theorizing has hitherto been mainly applied to perceptual and socio-cognitive development. In this thesis, I investigate whether a similar process of gradual specialization operates in motor development in infancy. I examine whether purposeful actions are initially ‘broadly tuned’ and widespread across limbs by measuring developmental changes in extraneous movements (movements in the other limbs that accompany the movement of a limb engaged in goal-directed action). In Study 1, I found a decrease in extraneous movements between 9- and 12-months of age in typically developing infants. I showed that this decrease is related to improvements in selective attention and amount of motor experience. In Study 2, I demonstrated that spatiotemporal coupling of both arms is a general characteristic of motor functioning in early infancy, and that this coupling declines between 9- and 12-months of age. Furthermore, I observed increased coupling with speed. In Study 3, I showed that extraneous movements are linked to, and likely limit, functional behaviour (in this case, intermanual coordination). Based on this series of studies with typically developing infants, I concluded that infant motor activity starts out broadly tuned and becomes progressively specialized over development. I subsequently extended my investigation to include atypically developing infants and toddlers (with Down syndrome). In Study 4, I showed that motor specialization in Down syndrome was more delayed than expected for children at their developmental level. Taken together with evidence that motor difficulties often appear before the onset of other behavioural symptomatology in disorders of unclear aetiology (e.g., ASD, ADHD), this opens up an important line of research in the possibility of using extraneous movements as an early marker of neurodevelopmental difficulties.