A small population of brain cells living in the cortex, not deep in the brain, appears able to switch an entire brain into sleep mode.
In a study published in Nature, researchers Geoffrey Terral and Renata Batista-Brito of the Albert Einstein College of Medicine identified a group of inhibitory cortical neurons that make up roughly one percent of the cortex's inhibitory cell population. When the team artificially activated these cells in mice, the animals fell asleep. That result cuts against the standard model in sleep research, which has long treated the cortex as a passive screen that displays slow-wave sleep rhythms generated elsewhere, in subcortical structures. Terral said sleep is usually associated with being controlled by subcortical regions, but this finding suggests the cortex can generate that control signal on its own.
The result matters because it reframes where scientists should look for the source of sleep control, not just where its effects show up. If a small, specific cortical circuit can initiate sleep, it becomes a far more tractable target for future research than the broad brainstem and hypothalamic networks that have dominated the field's attention.
It is worth remembering this is mouse data from artificially triggered neurons, not proof of how sleep normally starts in an intact brain. A switch that can turn a lamp on is not necessarily the switch that gets flipped every night.