Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, United States.
School of Biological Sciences, Georgia Institute of Technology, Atlanta, United States.
Elife. 2024 Oct 14;13:RP98841. doi: 10.7554/eLife.98841.
Locomotion in mammals is directly controlled by the spinal neuronal network, operating under the control of supraspinal signals and somatosensory feedback that interact with each other. However, the functional architecture of the spinal locomotor network, its operation regimes, and the role of supraspinal and sensory feedback in different locomotor behaviors, including at different speeds, remain unclear. We developed a computational model of spinal locomotor circuits receiving supraspinal drives and limb sensory feedback that could reproduce multiple experimental data obtained in intact and spinal-transected cats during tied-belt and split-belt treadmill locomotion. We provide evidence that the spinal locomotor network operates in different regimes depending on locomotor speed. In an intact system, at slow speeds (<0.4 m/s), the spinal network operates in a non-oscillating state-machine regime and requires sensory feedback or external inputs for phase transitions. Removing sensory feedback related to limb extension prevents locomotor oscillations at slow speeds. With increasing speed and supraspinal drives, the spinal network switches to a flexor-driven oscillatory regime and then to a classical half-center regime. Following spinal transection, the model predicts that the spinal network can only operate in the state-machine regime. Our results suggest that the spinal network operates in different regimes for slow exploratory and fast escape locomotor behaviors, making use of different control mechanisms.
哺乳动物的运动是由脊髓神经元网络直接控制的，它在来自上位脑的信号和与这些信号相互作用的躯体感觉反馈的控制下运作。然而，脊髓运动网络的功能结构、其运行模式，以及上位脑和感觉反馈在不同运动行为（包括不同速度下）中的作用仍不清楚。我们开发了一个接受上位脑驱动和肢体感觉反馈的脊髓运动回路的计算模型，该模型可以再现完整和脊髓横切猫在绑带和分带跑步机运动中获得的多个实验数据。我们提供的证据表明，脊髓运动网络根据运动速度在不同模式下运行。在一个完整的系统中，在较慢的速度（<0.4 m/s）下，脊髓网络在非振荡状态机模式下运行，并且需要感觉反馈或外部输入来进行相位转变。去除与肢体伸展相关的感觉反馈会阻止在较慢速度下的运动振荡。随着速度和上位脑驱动的增加，脊髓网络切换到屈肌驱动的振荡模式，然后切换到经典的半中心模式。脊髓横切后，模型预测脊髓网络只能在状态机模式下运行。我们的结果表明，脊髓网络在用于探索的慢速和用于逃避的快速运动行为中以不同的模式运行，利用不同的控制机制。
