Adjusting gait step-by-step: Brain activation during split-belt treadmill walking.

When walking on a split-belt treadmill, where each leg is driven at a different speed, a temporary change is made to the typical steady-state walking pattern. The exact ways in which the brain controls these temporary changes to walking are still unknown. Ten young adults (23±3y) walked on a split-belt treadmill for 30 min on 2 separate occasions: tied-belt control with both belts at comfortable walking speed, and continuous adjustment where speed ratio between belts changed every 15 seconds. 18F-fluorodeoxyglucose (18FDG) positron emission tomography (PET) imaging measured whole brain glucose metabolism distribution, or activation, during each treadmill walking condition. The continuous adjustment condition, compared to the tied-belt control, was associated with increased activity of supplementary motor areas (SMA), posterior parietal cortex (PPC), anterior cingulate cortex and anterior lateral cerebellum, and decreased activity of posterior cingulate and medial prefrontal cortex. In addition, peak activation of the PPC, SMA and PFC were correlated with cadence and temporal gait variability. We propose that a "fine-tuning" network for human locomotion exists which includes brain areas for sensorimotor integration, motor planning and goal directed attention. These findings suggest that distinct regions govern the inherent flexibility of the human locomotor plan to maintain a successful and adjustable walking pattern.