School of Psychology and Neuroscience, University of St. Andrews, St Andrews, Fife, KY16 9TS, United Kingdom, School of Computing and Mathematics, Plymouth University, Plymouth, Devon, PL4 8AA, United Kingdom, and Institute of Mathematical Problems in Biology, Russian Academy of Sciences, 142290, Pushchino, Russia.
J Neurosci. 2014 Apr 23;34(17):6065-77. doi: 10.1523/JNEUROSCI.4198-13.2014.
Many neural circuits are capable of generating multiple stereotyped outputs after different sensory inputs or neuromodulation. We have previously identified the central pattern generator (CPG) for Xenopus tadpole swimming that involves antiphase oscillations of activity between the left and right sides. Here we analyze the cellular basis for spontaneous left-right motor synchrony characterized by simultaneous bursting on both sides at twice the swimming frequency. Spontaneous synchrony bouts are rare in most tadpoles, and they instantly emerge from and switch back to swimming, most frequently within the first second after skin stimulation. Analyses show that only neurons that are active during swimming fire action potentials in synchrony, suggesting both output patterns derive from the same neural circuit. The firing of excitatory descending interneurons (dINs) leads that of other types of neurons in synchrony as it does in swimming. During synchrony, the time window between phasic excitation and inhibition is 7.9 ± 1 ms, shorter than that in swimming (41 ± 2.3 ms). The occasional, extra midcycle firing of dINs during swimming may initiate synchrony, and mismatches of timing in the left and right activity can switch synchrony back to swimming. Computer modeling supports these findings by showing that the same neural network, in which reciprocal inhibition mediates rebound firing, can generate both swimming and synchrony without circuit reconfiguration. Modeling also shows that lengthening the time window between phasic excitation and inhibition by increasing dIN synaptic/conduction delay can improve the stability of synchrony.
许多神经回路能够在不同的感觉输入或神经调制后产生多种定型的输出。我们之前已经确定了参与非洲爪蟾幼体游泳的中枢模式发生器（CPG），其涉及到左右两侧活动的反相振荡。在这里，我们分析了自发的左右运动同步的细胞基础，其特征是两侧以游泳频率的两倍同时爆发。在大多数幼体中，自发同步爆发很少见，它们最常出现在皮肤刺激后的第一秒内，并且会立即从游泳状态中出现并切换回游泳状态。分析表明，只有在游泳期间活跃的神经元才会同步发出动作电位，这表明两种输出模式都源自相同的神经回路。兴奋性下行中间神经元（dIN）的放电与游泳时一样，会使其他类型的神经元同步放电。在同步期间，相位激发和抑制之间的时间窗口为 7.9±1ms，短于游泳时的 41±2.3ms。在游泳期间，dIN 偶尔会在中期额外放电，这可能会引发同步，而左右活动的定时不匹配会将同步切换回游泳状态。计算机模型通过显示相同的神经网络（其中相互抑制介导反弹放电）可以在不重新配置电路的情况下产生游泳和同步，从而支持这些发现。模型还表明，通过增加 dIN 突触/传导延迟来延长相位激发和抑制之间的时间窗口，可以提高同步的稳定性。
