[Control mechanisms of locomotor movements from a viewpoint of behavioral control]

Locomotor movements are generally considered to be established by integrating the activities of the neuronal mechanisms related to each of the "automatic" and "volitional" control. As one of the neuronal mechanisms contributing to such integration, the possible roles played by the ponto-medullary reticular formation have recently been reexamined. As is well established, cells in the ponto-medullary reticular formation are related to arousal behavior, and the reticular formation itself is one of the major sources for generalized motor drive. In intact, awake cats, electrical stimulation delivered directly or indirectly to the reticular formation can evoke locomotor movements accompanied by an "alerting response" and preceded by postural adjustments adequate for locomotion. Microinjection of bethanechol, a short-acting cholinergic agonist, into the pontine reticular formation results in a peculiar modification of posture and, as a consequence, locomotor movements, even changing the arousal level of the animals. The cats with bilateral tegmental lesions in the pons exhibit locomotor movements during a state of rapid eye movement sleep without atonia. It is conceivable that the ponto-medullary reticular formation contributes greatly to the integration of neuronal activities related to automatic and volitional control of locomotor movements so as to establish a goal-directed behavioral locomotor movement.