Yaguchi Hiroaki, Takei Tomohiko, Kowalski David, Suzuki Takafumi, Mabuchi Kunihiko, Seki Kazuhiko
Department of Neurophysiology, National Institute of Neuroscience, Tokyo 187-8502, Japan, Graduate School of Information Science and Technology, The University of Tokyo, Tokyo 113-8656, Japan.
Department of Neurophysiology, National Institute of Neuroscience, Tokyo 187-8502, Japan.
J Neurosci. 2015 Apr 29;35(17):6937-45. doi: 10.1523/JNEUROSCI.3846-14.2015.
Proper execution of voluntary movement requires a sensorimotor transformation based on the initial limb state. For example, successfully reaching to a stable target requires the recruitment of different muscle groups depending on limb position at movement initiation. To test whether this transformation could occur at the spinal level, we stimulated the cervical spinal cord of anesthetized monkeys while systematically changing initial posture and examined the modulation of the twitch response induced in the upper limb muscles. In three monkeys, a multichannel microelectrode array was implanted into the C6 segment of the spinal cord and electromyographic electrodes were implanted in 12 limb muscles (five hand, four elbow, and three shoulder muscles). The magnitude and onset latency of the evoked response in each electrode-muscle pair were examined by systematically changing the hand position through nine positions in a horizontal plane with the monkey prone. Among 330 electrode-muscle pairs examined, 61% of pairs exhibited significant modulation of either magnitude or latency of twitch responses across different hand/arm configurations (posture dependency). We found that posture dependency occurred preferentially in the distal rather than proximal muscles and was not affected by the location of the electrode within the stimulated spinal segment. Importantly, this posture dependency was not affected by spinalization at the C2 level. These results suggest that excitability in the cervical spinal cord is affected by initial arm posture through spinal reflex pathways. This posture dependency of spinal motor output could affect voluntary arm movement by adjusting descending motor commands relative to the initial arm posture.
正确执行自主运动需要基于肢体初始状态进行感觉运动转换。例如，成功够到一个稳定目标需要根据运动起始时的肢体位置募集不同的肌肉群。为了测试这种转换是否能在脊髓水平发生，我们在系统改变初始姿势的同时刺激麻醉猴子的颈脊髓，并检查上肢肌肉中诱发的抽搐反应的调制情况。在三只猴子中，将一个多通道微电极阵列植入脊髓的C6节段，并将肌电图电极植入12块肢体肌肉（五块手部肌肉、四块肘部肌肉和三块肩部肌肉）。通过让猴子俯卧在水平面上，将手部位置系统地改变九个位置，来检查每个电极 - 肌肉对中诱发反应的幅度和起始潜伏期。在检查的330个电极 - 肌肉对中，61%的对在不同的手部/手臂配置（姿势依赖性）下表现出抽搐反应幅度或潜伏期的显著调制。我们发现姿势依赖性优先发生在远端而非近端肌肉中，并且不受刺激脊髓节段内电极位置的影响。重要的是，这种姿势依赖性不受C2水平脊髓横断的影响。这些结果表明，颈脊髓的兴奋性通过脊髓反射通路受到初始手臂姿势的影响。脊髓运动输出的这种姿势依赖性可能通过相对于初始手臂姿势调整下行运动指令来影响自主手臂运动。
