Developmental trajectory of neural activity underlying motor control differs by sequence complexity and motor stage.

Primary motor areas in the brain mature relatively early in development, yet the control of complex movements improves through early adulthood. Neural oscillations in higher-order regions are refined in adolescence and contribute to executive processes important for complex motor control, but the neural dynamics among these regions and primary motor cortices remain poorly understood in youth. We recorded magnetoencephalography during a motor sequencing task in 68 healthy youth from ten to 17 years of age. Significant changes in oscillatory activity relative to baseline were identified at the sensor level and source reconstructed with a beamformer. Whole-brain maps of beta (18-24 Hz) and gamma (74-84 Hz) oscillatory activity were subjected to voxel-wise repeated-measures ANCOVAs to identify brain areas in which the developmental trajectory of oscillatory power differed by sequence complexity (simple/complex) or motor stage (planning/execution). Beta activity in bilateral prefrontal cortices was weaker with age during the planning of complex movements. Across simple and complex conditions, older youth tended to have stronger beta in posterior areas during planning. Finally, gamma activity across conditions was stronger with age in occipital and weaker in temporal cortices. These results suggest that the functional refinement of association cortices may drive improvements in motor control by enabling more efficient attentional and inhibitory control during formulation of the motor plan.