Motor systems implement diverse motor programs to pattern behavioral sequences, yet how different motor actions are controlled on a moment-by-moment basis remains unclear. Here, we investigated the neural circuit mechanisms underlying the control of distinct courtship songs in Drosophila. Courting males rapidly alternate between two types of song: pulse and sine. By recording calcium signals in the ventral nerve cord in singing flies, we found that one neural population is active during both songs, whereas an expanded neural population, which includes neurons from the first population, is active during pulse song. Brain recordings showed that this nested activation pattern is present in two descending pathways required for singing. Connectomic analysis reveals that these two descending pathways provide structured input to ventral nerve cord neurons in a manner consistent with their activation patterns. These results suggest that nested premotor circuit activity, directed by distinct descending signals, enables rapid switching between motor actions.

运动系统实施不同的运动程序来模式化行为序列，但如何每时每刻控制不同的运动动作仍不清楚。在这里，我们研究了果蝇控制不同求偶歌曲的神经回路机制。求爱的雄性在两种类型的歌声之间迅速交替：脉搏和正弦。通过记录唱歌的苍蝇腹侧神经索中的钙信号，我们发现一个神经种群在两首歌中都很活跃，而一个扩大的神经种群，包括来自第一个种群的神经元，在脉搏歌声中很活跃。大脑记录显示，这种嵌套激活模式存在于唱歌所需的两条下降路径中。连接组学分析表明，这两个下降途径以与其激活模式一致的方式为腹侧神经索神经元提供结构化输入。这些结果表明，由不同的下降信号指导的嵌套前运动电路活动可以在运动动作之间快速切换。