Reactive and anticipatory control of posture and bipedal locomotion in a nonhuman primate

Bipedal locomotion is a common daily activity. Despite its apparent simplicity, it is a complex set of movements that requires the integrated neural control of multiple body segments. We have recently shown that the juvenile Japanese monkey, M. fuscata, can be operant-trained to walk bipedally on moving treadmill. It can control the body axis and lower limb movements when confronted by a change in treadmill speed. M. fuscata can also walk bipedally on a slanted treadmill. Furthermore, it can learn to clear an obstacle attached to the treadmill's belt. When failing to clear the obstacle, the monkey stumbles but quickly corrects its posture and the associated movements of multiple motor segments to again resume smooth bipedal walking. These results give indication that in learning to walk bipedally, M. fuscata transforms relevant visual, vestibular, proprioceptive, and exteroceptive sensory inputs into commands that engage both anticipatory and reactive motor mechanisms. Both mechanisms are essential for meeting external demands imposed upon posture and locomotion.