Although the mammalian rest-activity cycle is controlled by a “master clock” in the suprachiasmatic nucleus (SCN) of the hypothalamus, it is unclear how firing of individual SCN neurons gates individual features of daily activity. Here, we demonstrate that a specific transcriptomically identified population of mouse VIP+ SCN neurons is active at the “wrong” time of day—nighttime—when most SCN neurons are silent. Using chemogenetic and optogenetic strategies, we show that these neurons and their cellular clocks are necessary and sufficient to gate and time nighttime sleep but have no effect upon daytime sleep. We propose that mouse nighttime sleep, analogous to the human siesta, is a “hard-wired” property gated by specific neurons of the master clock to favor subsequent alertness prior to dawn (a circadian “wake maintenance zone”). Thus, the SCN is not simply a 24-h metronome: specific populations sculpt critical features of the sleep-wake cycle.

尽管哺乳动物的休息活动周期是由下丘脑上眼睑上核（SCN）中的“主时钟”控制的，但尚不清楚单个SCN神经元的放电如何控制日常活动的各个特征。在这里，我们证明了特定的转录组识别的小鼠VIP + SCN神经元群体在白天的“错误”时间（夜间）活跃，而大多数SCN神经元却保持沉默。使用化学和光遗传学策略，我们表明，这些神经元及其细胞时钟对于夜间睡眠门控和计时非常必要，但对白天睡眠没有影响。我们建议，小鼠夜间睡眠类似于人的午睡，是由主时钟的特定神经元控制的“硬连线”属性，以利于黎明前的后续机敏（昼夜节律“唤醒维持区”）。从而，