Cohen Oren, Harel Ran, Aumann Tim D, Israel Zvi, Prut Yifat
Department of Medical Neurobiology, Institute for Medical Research Israel-Canada and The Edmond & Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Hadassah Medical School, Jerusalem, Israel.
Department of Neurosurgery, Sheba Medical Center, Tel Aviv, Israel.
J Neurophysiol. 2017 Jul 1;118(1):254-266. doi: 10.1152/jn.00825.2016. Epub 2017 Apr 5.
Cerebellar control of voluntary movements is achieved by the integration of external and internal feedback information to adjust and correct properly ongoing actions. In the forelimb of primates, rostral-spinocerebellar tract (RSCT) neurons are thought to integrate segmental, descending, and afferent sources and relay upstream a compound signal that contains both an efference copy of the spinal-level motor command and the state of the periphery. We tested this hypothesis by implanting stimulating electrodes in the superior cerebellar peduncle and recording the activity of cervical spinal neurons in primates. To dissociate motor commands and proprioceptive signals, we used a voluntary wrist task and applied external perturbations to the movement. We identified a large group of antidromically activated RSCT neurons located in deep dorsal sites and a smaller fraction of postsynaptically activated (PSA) cells located in intermediate and ventral laminae. RSCT cells received sensory input from broad, proximally biased receptive fields (RFs) and were not affected by applied wrist perturbations. PSA cells received sensory information from distal RFs and were more strongly related to active and passive movements. The anatomical and functional properties of RSCT and PSA cells suggest that descending signals converging on PSA cells contribute to both motor preparation and motor control. In parallel, RSCT neurons relay upstream an integrated signal that encodes the state of working muscles and can contribute to distal-to-proximal coordination of action. Thus the rostral spinocerebellar system sends upstream an efference copy of the motor command but does not signal abrupt errors in the performed movement. Cerebellar coordination of voluntary movements relies on integrating feedback information to update motor output. With the use of a novel protocol, we identified spinal neurons constituting the ascending and descending components of the forelimb spinocerebellar system in behaving primates. The data suggest that descending information contributes to both motor preparation and execution, whereas ascending information conveys the spinal level motor command, such that internal and external feedback is relayed through parallel pathways.
小脑对随意运动的控制是通过整合外部和内部反馈信息来实现的，以适当调整和纠正正在进行的动作。在灵长类动物的前肢中，嘴侧脊髓小脑束（RSCT）神经元被认为整合了节段性、下行性和传入性信号源，并向上游传递一个复合信号，该信号既包含脊髓水平运动指令的传出拷贝，也包含外周的状态信息。我们通过在灵长类动物的上小脑脚植入刺激电极并记录颈脊髓神经元的活动来验证这一假设。为了区分运动指令和本体感觉信号，我们使用了一个随意的腕部任务，并对运动施加外部干扰。我们识别出一大群位于背侧深部的经逆向激活的RSCT神经元，以及一小部分位于中间层和腹侧层的突触后激活（PSA）细胞。RSCT细胞从广泛的、近端偏向的感受野（RFs）接收感觉输入，并且不受施加的腕部干扰的影响。PSA细胞从远端RFs接收感觉信息，并且与主动和被动运动的关系更强。RSCT和PSA细胞的解剖学和功能特性表明，汇聚在PSA细胞上的下行信号有助于运动准备和运动控制。同时，RSCT神经元向上游传递一个整合信号，该信号编码工作肌肉的状态，并有助于动作从远端到近端的协调。因此，嘴侧脊髓小脑系统向上游发送运动指令的传出拷贝，但不发出所执行运动中的突然错误信号。小脑对随意运动的协调依赖于整合反馈信息以更新运动输出。通过使用一种新的方案，我们在行为中的灵长类动物中识别出构成前肢脊髓小脑系统上行和下行成分的脊髓神经元。数据表明，下行信息有助于运动准备和执行，而上行信息传达脊髓水平的运动指令，使得内部和外部反馈通过并行途径传递。
