Adaptive mechanisms coupling the four limbs during quadrupedal locomotion

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In terrestrial mammals, including humans, walking involves coordinated activity of all four limbs. Although mechanisms coordinating the arms and legs during walking are poorly understood, it is thought that a linkage between functional networks located at the cervical and lumbosacral levels of the spinal cord are involved. The goal of this study is to investigate some of the reflex pathways that couple the cervical and lumbosacral networks of the spinal cord during quadrupedal treadmill locomotion in the cat, in conditions where these networks can be functionally uncoupled. To accomplish this goal, quadrupedal locomotion will be studied on a 4-way split-belt treadmill that can uncouple the rhythm (i.e. speed) of each leg, thus separating the functioning of the spinal networks controlling each limb. Cats will be implanted with recording and stimulating electrodes to record muscular activity in all four limbs and to stimulate peripheral nerves, respectively. The nerve stimulation will be done to evoke reflex responses that couple the arms and legs. For instance, the nerves supplying the dorsum of the foot and forepaw will be stimulated to evoke reflex responses in muscles of the forelimbs and hindlimbs, respectively. The goal is to study these reflex pathways during quadrupedal locomotion when the four limbs walk at the same speed and under conditions where the rhythm of each limb is independently controlled using various combinations. Such an approach, will demonstrate how reflex pathways adapt under these conditions, and also provide mechanistic insight as to the role of sensory feedback in regulating the activity of networks located at one girdle (e.g. arms) to another (e.g. legs). The experimental data will provide a framework to systematically investigate the neural structures involved in the control and adaptation of quadrupedal locomotion.