Zarzecki P, Kirchberger P, Istvan P
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
Acta Neurobiol Exp (Wars). 1993;53(1):113-24.
Neurons project out of motor cortex to the spinal cord and to other targets. Not all projection neurons recruit in the same way during behavior, but instead recruitment patterns depend on the projection target of the neurons. The problem is to understand how neurons projecting to different targets are recruited selectively. We have investigated possible mechanisms for the recruitment of motor cortex neurons with electrophysiological approaches in anesthetized cats. To determine if neurons projecting out of motor cortex to different targets have selective input connectivity from extrinsic sources we electrically stimulated corticocortical, callosal and thalamocortical pathways. Subthreshold effects of input pathways were detected by monitoring latency variations of antidromic responses. Intracortical connections to identified output neurons were evaluated by cross-correlation and a new variation of the antidromic latency method. Output neurons in different layers along single electrode tracks usually had different inputs from extrinsic sources. Neurons in close proximity were most likely to share the same inputs, especially when they projected axons to the same target. These results support the conclusion that combinations of inputs from extrinsic sources could selectively recruit efferent neurons from separate cortical layers or from within groups of nearby neurons, according to the target of their axonal projections. In contrast, the data on intracortical connectivity suggest that common drive causes a more synchronous activation of nearby cortical neurons. Combining the conclusions on effects of inputs from extrinsic and intracortical sources leads to the speculation that motor cortex neurons that might at one time be recruited selectively by action of extrinsic afferent pathways to cortex could at another time be bound into synchrony by a common drive shared with their neighbours.
神经元从运动皮层投射到脊髓及其他目标区域。并非所有投射神经元在行为过程中的募集方式都相同，相反，募集模式取决于神经元的投射目标。问题在于理解投射到不同目标的神经元是如何被选择性募集的。我们运用电生理方法在麻醉猫身上研究了运动皮层神经元募集的可能机制。为了确定从运动皮层投射到不同目标的神经元是否具有来自外部源的选择性输入连接，我们电刺激了皮质皮质、胼胝体和丘脑皮质通路。通过监测逆行反应的潜伏期变化来检测输入通路的阈下效应。通过互相关和逆行潜伏期方法的一种新变体来评估与已识别输出神经元的皮质内连接。沿单电极轨迹不同层的输出神经元通常具有来自外部源的不同输入。相邻的神经元最有可能共享相同的输入，尤其是当它们将轴突投射到相同目标时。这些结果支持这样的结论：根据其轴突投射的目标，来自外部源的输入组合可以选择性地募集来自不同皮质层或附近神经元组内的传出神经元。相比之下，关于皮质内连接的数据表明，共同驱动会导致附近皮质神经元更同步的激活。结合关于来自外部和皮质内源性输入效应的结论，引发了这样的推测：运动皮层神经元可能在某一时刻通过外部传入通路对皮层的作用而被选择性募集，而在另一时刻可能通过与其相邻神经元共享的共同驱动而同步激活。
