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Brain substrates of sensorimotor control during upper and lower limb coordination in youth

Book - Dissertation

Motor control skills develop rapidly during the first years of life. The relatively fast development of motor control in early childhood, is followed by an extended period of motor refinement into adolescence and adulthood. This refinement is particularly seen in more complex motor tasks which require elaborate cortical processes. The extent to which brain maturation contributes to motor control from childhood to adolescence is, however, not well understood. Therefore, this dissertation aimed to elucidate the relationship between motor refinement and brain maturation in 8-19 year olds.In the first part of this dissertation, I investigated the sensory contributions (i.e., vision and proprioception) to a dynamical bimanual tracking task, and what brain structures predicted performance. It was found that the relative contributions of vision and proprioception to tracking performance were similar across the age span of 8-19 years. Furthermore, the microstructural organization of neural connections between the dorsolateral prefrontal cortices, and the thickness of the primary motor cortices, were associated with sensory-specific tracking performance accuracy across all ages. Overall, these findings suggested that youth aged 8-19 years use sensory information in an adult-like manner during bimanual tracking, and this performance relies on brain regions involved in both sensorimotor processes and attention and working memory.The second part of this dissertation focused on the control of complex forms of gait. Firstly, we investigated the development of the skill to create and deploy proper anticipatory strategies in response to an obstacle in the walkway. Results showed that the level of cautiousness of gait strategies reduced with age. This was revealed by an attenuation of step width modifications, reductions of feet-obstacle distances, and lower feet lifts during obstacle crossing. In anticipation to the obstacle, however, step length and speed adjustments during successful obstacle avoidance were similar across all ages. Moreover, during unsuccessful trials, younger children misjudged the distance to the obstacle which resulted in exaggerated take-off distances, followed by obstacle contact upon the next heel strike. Overall, these results indicated that obstacle avoidance strategies were refined throughout childhood into adolescence, particularly concerning the precise control of foot placements near the obstacle. Secondly, we investigated the neuro-behavioral relationships during a precision stepping task in which step targets could unexpectedly shift to new locations, forcing online step modifications. Main findings revealed that across all ages, step accuracy on non-shifting step targets was positively associated with the microstructural organization of frontal WM pathways. As these pathways convey information between frontal brain regions that are involved in attentional and visuospatial processes, these results may indirectly suggest that precision stepping on non-shifting step targets is driven by cortical processes across all ages. No significant neuro-behavioral correlations were found when stepping on shifting targets, suggesting that other (neural) mechanisms might be more important for this type of stepping.In conclusion, it was shown that the control of complex movements, both bimanual and gait, undergo ongoing refinement from childhood into adolescence. Moreover, the central levels of the sensorimotor system were associated with motor control accuracy in youth, above and beyond the effect of age. These findings suggest that frontal WM pathways that convey neural information between brain regions involved in attentional processing, contribute to the perception and execution of complex motor tasks. This work contributes to the understanding of the mechanisms underlying motor control in typically developing children, which may ultimately be beneficial for clinical approaches to help children with motor disabilities.