NEURONAL NETWORK OF THE CENTRAL PATTERN GENERATOR FOR LOCOMOTION AND ITS CONTROL MECHANISMS

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Rhythmic locomotor activities of limb movements in quadrupeds are primarily generated by the central pattern generator (CPG) for locomotion. However, the neuronal substrate and mechanisms of pattern generation are still unknown. The CPG is controlled by the higher brain center. Initiation and termination of locomotion should be understood in terms of activation and inactivation of the CPG.Furthermore, in real locomotion the CPG output should be well adjusted for animals not to fall. In this project, we made five kinds of studies to understand neuronal control of locomotion and posture. (1) During repetitive stimulation of the locomotor command system to activate the CPG, motoneuronal responses to each stimulus pulse were analysed with intracellular recordings from forelimb motoneurons to reveal neuronal pathways connecting the input and output within the CPG.It was shown that the locomotor command was transmitted to flexor and extensor motoneurons via disynaptic and trisynaptic excitat … More ory pathways, respectively. The neurons of these pathways may be important members of the CPG.A neuronal network was proposed for the CPG.(2) A computor simulation revealed that the neuronal network could generate the locomotor rhythm. (3) The lateral hypothalamic area is one of the higher brain center to control initiation and termination of locomotion. Unit recording revealed there are locomotor-related neurons in the lateral hypothalamus. (4) Dynamic postural control during locomotion could be due to common neuronal mechanisms that maintain upright posture on the unstable platform. In human substances control of upright standing on rocking platforms was analysed with kinematics and electromyography. It was suggested that anticipatory adjustments were essential for dynamic postural control. (5) Righting reflex may be a basic neuronal machine for dynamic postural control. Analyses of air-righting reflex of rats with lesions of various brain areas suggested that the basal ganglia was a important center to modify postural adjustment during falling. Less