Neural mechanisms underlying upright bipedal gait: role of cortico-brainstem-spinal pathways involved in posture-gait control

Bipedal gait involves moving the body while maintaining an upright posture under gravity. Throughout vertebrate evolution and postnatal development, humans acquired antigravity functions that allow one to achieve biped gait. While walking, our attention is focused on purposeful, intentional movements such as dexterous arm-hand finger movements or searching for the target. On the other hand, postural control comes to our awareness only when we need to alter gait patterns, such as facing demanding conditions. Nonetheless, our body and brain control gait so as not to fall by anticipatorily adjusting posture that optimally achieves multi-tasks consisting of purposeful movements and walking. Accordingly, we have developed the working hypothesis that postural control is achieved by plans and programs that accomplish purposeful actions. Key questions to verify this hypothesis are (1) how higher brain functions brought about by evolution enabled us to acquire a bipedal standing posture that resists gravity and (2) how the frontal cortex, the most developed neocortical area, enabled us to acquire multi-tasks consisting of gait and intentional movements. We postulate that the frontoparietal networks that contribute to planning and programming based on cognitive information and corticofugal pathways that issue command signals to the subcortical structures, particularly the brainstem and spinal cord in which core systems of posture and gait control exist, play central roles in solving these questions. These mechanisms may be declined in older adults and impaired in patients with degenerative neurological disorders, resulting in posture-gait disturbance such as freezing of gait (FOG) and falling.