MOTOR CORTICAL ACTIVITY DURING VOLUNTARY GAIT MODIFICATIONS IN THE CAT .1. CELLS RELATED TO THE FORELIMBS
MOTOR CORTICAL ACTIVITY DURING VOLUNTARY GAIT MODIFICATIONS IN THE CAT .1. CELLS RELATED TO THE FORELIMBS
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DOI：
10.1152/jn.1993.70.1.179
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发表时间：
1993-07-01
影响因子：
2.5
通讯作者：
DREW, T
中科院分区：
文献类型：
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作者：
DREW, T
1.在自主改变步态时，记录了91个已识别的锥体束神经元(PTN)的放电模式，这些神经元位于猫运动皮质第4区的前肢区。同时记录的是肩部、肘部、手腕周围的屈肌和伸肌，以及与记录部位对侧的前肢的手指。对步态改变过程中肌电(EMG)活动变化的分析表明，当对侧前肢率先越过障碍时，肩部和肘部的大部分屈肌以及手腕和指背屈肌的活动都增加了。这一增强活动期可以细分为两个部分：一个与肢体的初始屈曲有关，这是使其越过和越过障碍物所需的(阶段I)，第二个阶段与足部接触之前腕背屈肌活动增加有关(阶段II)。在步态改变过程中，当记录部位的对侧肢体最先跨过障碍时，共有57/91个(63%)记录的PTN的放电频率显著增加；其中6个神经元在步态周期的不同部分也表现出明显的放电减少。在另外21/91(23%)个神经元中，放电频率仅降低，而其余13/91(14%)个PTN在对照行走和步态改变时表现出相似的活动模式。4.大部分放电频率显著增加的神经元(47/57)在生理屈肌活动增强期间放电最多。其中23个(23/47)细胞在第一阶段最大放电，12(12/47)细胞在第二阶段最大放电。第三组PTN(12/47)在紧接改进周期之前的阶跃周期的站立阶段开始增加它们的放电。7个(7/57)PTN在修正周期的站立阶段增加了放电，其余3个不能归类为优先与阶跃周期的任何一个部分有关。5.当记录部位对侧小腿第二个遇到障碍物时，41/57个PTNS的调频较小。在许多神经元中，峰值放电发生的阶跃周期的时间也有明显的变化。这些幅度和时间上的变化与观察到的肌肉时间关系的变化是平行的。6.73个PTN中有71个可确定感受野。共有54/71个PTN具有包括前爪在内的感受野，55/71个PTN通过轻刷皮肤表面(皮肤感受野)激活。在大多数情况下，无论是控制行走过程中细胞的放电，还是跨过障碍物时的放电，都不能根据感受野来解释或预测。在极端情况下，在步态调整的摆动阶段，接受野局限于爪底表面的PTN会被释放。这表明，在大多数情况下，细胞放电的增加是由于视觉触发的中枢输入，而不是外周输入。比较对侧肢体牵拉时和牵拉时运动皮质神经元的相对激活时间，提示这些PTN可以分为不同的细胞群，在小窝修饰过程中不同时间处于活跃状态。研究表明，这些群体中的每一个都可能通过调节中间神经元的活动来调节在步长周期中不同时间活跃的肌肉的活动，中间神经元是运动中枢模式生成器的一部分，或者受中央模式生成器的影响。
1. The discharge patterns of 91 identified pyramidal tract neurons (PTNs), located within the forelimb region of area 4 of the cat motor cortex, were recorded during the voluntary modifications of gait needed to step over obstacles attached to a moving treadmill belt. Recordings were made simultaneously from flexor and extensor muscles acting around the shoulder, elbow, wrist, and digits of the forelimb contralateral to the recording site.2. Analysis of the changes in electromyographic (EMG) activity during the gait modification showed increases in the activity of most flexor muscles of the shoulder and elbow, as well as in the wrist and digit dorsiflexors, when the contralateral forelimb was the first to pass over the obstacle. This period of augmented activity could be subdivided into two parts: one associated with the initial flexion of the limb that was needed to bring it above and over the obstacle (phase I), and the second associated with increased wrist dorsiflexor muscle activity before foot contact (phase II).3. The discharge frequency of a total of 57/91 (63%) of the recorded PTNs was significantly increased during the gait modification when the limb contralateral to the recording site was the first to step over the obstacle; six of these neurons also showed a significant decrease in their discharge in a different part of the step cycle. In a further 21/91 (23%) neurons, discharge frequency was only decreased, whereas the remaining 13/91 (14%) PTNs showed similar patterns of activity both during control walking and during the gait modifications. 4. Most of those neurons (47/57) in which significant increases in firing frequency were observed, discharged maximally during the period of increased activity of the physiological flexor muscles. Twenty-three of these cells (23/47) discharged maximally in phase I, and 12 (12/47) in phase II. A third population of PTNS (12/47) started to increase their discharge in the stance phase of the step cycle immediately preceding the modified cycle. Seven (7/57) PTNs increased their discharge during the stance phase of the modified cycle, and the remaining three could not be classified as being preferentially related to any one part of the step cycle. 5. The frequency modulation of 41/57 PTNs was less when the leg contralateral to the recording site was the second to encounter the obstacle. In many neurons there was also an appreciable change in the time in the step cycle that peak discharge occurred. These changes in amplitude and timing paralleled the changes observed in the temporal relationships of the muscles. 6. Receptive fields could be determined for 71 of the 73 PTNs tested. Altogether 54/71 PTNs had receptive fields that included the forepaw, and 55/71 PTNs were activated by light brushing of the skin surface (cutaneous receptive fields). In most cases neither the discharge of the cell during control walking, nor its discharge during the steps over the obstacles, could be explained, or predicted, on the basis of the receptive field. In the extreme case, PTNs with receptive fields restricted to the plantar surface of the paw discharged during the swing phase of the gait modification. It is suggested that in most cases the increase in cell discharge is due to visually triggered central, rather than peripheral, inputs.7. Comparison of the relative time of activation of motor cortical neurons when the contralateral limb led, and when it trailed, suggested that these PTNs could be divided into different populations of cells active at different times during the pit modification. It is suggested that each of these populations may regulate the activity of muscles active at different times in the step cycle by modulating the activity of interneurons that either form part of, or that are influenced by, the central pattern generator for locomotion.