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首页> 外文期刊>Journal of Neurophysiology >Postnatal development of the motor representation in primary motor cortex.
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Postnatal development of the motor representation in primary motor cortex.

机译：初级运动皮层运动表现的产后发展。

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The purpose of this study was to examine when the muscles and joints of the forelimb become represented in primary motor cortex (M1) during postnatal life and how local representation patterns change. We examined these questions in cats that were anesthetized (45-90 days, n = 14; adults, n = 3) and awake (n = 4; 52-86 days). We used intracortical microstimulation (45 ms duration train, 330 Hz, 0.2-ms balanced biphasic pulses, with a leading cathodic pulse; up to 100 microA). In young animals (less than day 70), we also used stimulus trains and pulses that could produce greater temporal summation (up to 200-ms train duration, down to 143-Hz stimulus frequency, up to 0.8-ms pulse width). Anesthetized animals were areflexic, and muscle tone was similar to that of the awake cats (i.e., relaxed, not weight or load bearing, with minimal resistance to passive stretch). We monitored the kinematic effects of microstimulation and changes in electromyographic (EMG) activity in forelimb muscles. There was an age-dependent reduction in the number of sites where microstimulation did not produce a motor effect (i.e., ineffective sites), from 95% in animals younger than 60 days to 33% between 81 and 90 days. In adults, 24% of sites were ineffective. Median current thresholds for evoking movements dropped from 79 microA in animals younger than day 60 to 38 and 28 microA in day 81-90 animals and adults, respectively. There was a proximal-to-distal development of the somatotopic organization of the motor map. Stimulation at the majority of sites in animals younger than day 71 produced shoulder and elbow movement. Wrist sites were first present by day 71, and digit sites by day 81. Sites at which multiple responses were evoked, between 1.0 and 1.5 times threshold, were present after day 71, and increased with age. A higher percentage of distal joints were co-represented with other joints, rather than being represented alone. We found that effective sites initially were scattered and new sites representing proximal and distal joints filled in the gaps between effective sites. During most of the period examined, development of the caudal M1 subregion lagged that of the rostral subregion (percent of effective sites; threshold currents), although these differences were minimal or absent in adults. Our results show that the M1 motor representation is absent at day 45 and, during the subsequent month, the motor map is constructed by progressively representing more distal forelimb joints.
机译：这项研究的目的是检查产后生活中前肢的肌肉和关节何时出现在初级运动皮层（M1）中，以及局部表达模式是如何变化的。我们在麻醉（45-90天，n = 14;成年，n = 3）和清醒（n = 4; 52-86天）的猫中检查了这些问题。我们使用了皮层内微刺激（持续时间为45 ms，330 Hz，0.2 ms的平衡双相脉冲，超前的阴极脉冲;最大100 microA）。在年幼的动物（少于第70天）中，我们还使用了刺激训练和脉冲，这些刺激和脉冲可能产生更大的时间累加（训练持续时间长达200毫秒，刺激频率降低至143 Hz，脉冲宽度高达0.8毫秒）。麻醉过的动物是弯曲的，并且肌肉的音调与清醒的猫类似（即放松，不承重或负重，对被动拉伸的抵抗力最小）。我们监测了微刺激的运动学影响以及前肢肌肉的肌电图（EMG）活动的变化。微刺激不产生运动作用的部位（即无效部位）的数量与年龄相关，从60天以下的动物中的95％降至81至90天之间的33％。在成年人中，有24％的部位无效。引起运动的当前阈值中值从小于60天的动物中的79 microA下降到第81-90天的动物和成年中的38 microA和28 microA。运动图的体位组织从近到远发展。在不超过71天的动物中，大多数部位的刺激都会引起肩膀和肘部运动。在第71天时首先出现腕部部位，在第81天时出现手指部位。在第71天后出现多个反应的部位，在阈值的1.0到1.5倍之间，并且随着年龄的增长而增加。较高比例的远端关节与其他关节共同代表，而不是单独代表。我们发现，有效部位最初是分散的，代表近端和远端关节的新部位填充了有效部位之间的间隙。在所检查的大部分时间里，尾部M1子区的发育落后于延髓部子区的发育（有效部位的百分比;阈值电流），尽管这些差异在成年人中很小或没有。我们的结果表明，在第45天不存在M1运动表现，并且在随后的一个月中，通过逐渐代表更多的远端前肢关节来构建运动图。

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