Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Centre de recherche du Centre Hospitalier de l'Université de Sherbrooke, Université de Sherbrooke, Sherbrooke, Quebec, Canada.
J Physiol. 2024 Jan;602(1):183-204. doi: 10.1113/JP285473. Epub 2023 Nov 28.
Mammals walk in different directions, such as forward and backward. In human infants/adults and decerebrate cats, one leg can walk forward and the other backward simultaneously on a split-belt treadmill, termed hybrid or bidirectional locomotion. The purpose of the present study was to determine if spinal sensorimotor circuits generate hybrid locomotion and if so, how the limbs remain coordinated. We tested hybrid locomotion in 11 intact cats and in five following complete spinal thoracic transection (spinal cats) at three treadmill speeds with the hindlimbs moving forward, backward or bidirectionally. All intact cats generated hybrid locomotion with the forelimbs on a stationary platform. Four of five spinal cats generated hybrid locomotion, also with the forelimbs on a stationary platform, but required perineal stimulation. During hybrid locomotion, intact and spinal cats positioned their forward and backward moving hindlimbs caudal and rostral to the hip, respectively. The hindlimbs maintained consistent left-right out-of-phase alternation in the different stepping directions. Our results suggest that spinal locomotor networks generate hybrid locomotion by following certain rules at phase transitions. We also found that stance duration determined cycle duration in the different locomotor directions/conditions, consistent with a common rhythm-generating mechanism for different locomotor directions. Our findings provide additional insight on how left-right spinal networks and sensory feedback from the limbs interact to coordinate the hindlimbs and provide stability during locomotion in different directions. KEY POINTS: Terrestrial mammals can walk forward and backward, which is controlled in part by spinal sensorimotor circuits. Humans and cats also perform bidirectional or hybrid locomotion on a split-belt treadmill with one leg going forward and the other going backward. We show that cats with a spinal transection can perform hybrid locomotion and maintain left-right out-of-phase coordination, indicating that spinal sensorimotor circuits can perform simultaneous forward and backward locomotion. We also show that the regulation of cycle duration and phase duration is conserved across stepping direction, consistent with a common rhythm-generating mechanism for different stepping directions. The results help us better understand how spinal networks controlling the left and right legs enable locomotion in different directions.
哺乳动物以不同的方向行走，例如前进和后退。在人类婴儿/成人和去大脑猫中，一条腿可以在分裂带跑步机上同时向前和向后行走，称为混合或双向运动。本研究的目的是确定脊髓感觉运动回路是否产生混合运动，如果是，四肢如何保持协调。我们在 11 只完整的猫和 5 只完全脊髓胸切断（脊髓猫）中测试了混合运动，在三种跑步机速度下，后腿向前、向后或双向移动。所有完整的猫在前肢固定在平台上时都会产生混合运动。5 只脊髓猫中的 4 只也产生了混合运动，前肢也固定在平台上，但需要会阴部刺激。在混合运动中，完整和脊髓猫将向前和向后移动的后肢定位在臀部的尾侧和头侧，分别。后肢在不同的步行动作方向中保持一致的左右异相交替。我们的结果表明，脊髓运动网络通过在相位转换时遵循某些规则来产生混合运动。我们还发现，在不同的运动方向/条件下，站立持续时间决定了周期持续时间，这与不同运动方向的共同节律产生机制一致。我们的发现提供了更多的见解，说明左右脊髓网络和来自四肢的感觉反馈如何相互作用，以协调后肢并在不同方向的运动中提供稳定性。 关键点：陆地哺乳动物可以向前和向后行走，部分由脊髓感觉运动回路控制。人类和猫也可以在分裂带跑步机上进行双向或混合运动，一条腿向前，另一条腿向后。我们表明，脊髓横断的猫可以进行混合运动并保持左右异相协调，表明脊髓感觉运动回路可以同时进行向前和向后运动。我们还表明，周期持续时间和相位持续时间的调节在步行动作方向上是保守的，这与不同步行动作方向的共同节律产生机制一致。结果有助于我们更好地理解控制左右腿的脊髓网络如何使不同方向的运动成为可能。
