Rare Sst-Chodl Cortical Neurons Actively Drive the Transition Into Sleep, Nature Study Finds
核心洞察
A Nature study led by Mount Sinai researchers identifies Sst-Chodl neurons (搜索) in the cerebral cortex as an active driver of sleep rather than a passive follower of deep brain centers.
Sst-Chodl neurons (搜索) make up roughly 0.2% of cortical neurons but send long-range signals capable of synchronizing activity across large areas of the brain.
Activating these neurons slowed and synchronized neocortical electrical activity and was sufficient to make mice fall asleep more readily and sleep longer.
A rare population of neurons in the cerebral cortex can synchronize activity across large areas of the brain and actively promote sleep, according to a study published September 9 in Nature. The findings challenge a nearly century-old model in which sleep is governed solely by structures deep within the brain while the cortex passively follows.
The research, led by Renata Batista-Brito, PhD, Associate Professor of Neuroscience at the Icahn School of Medicine at Mount Sinai, identified neurons called Sst-Chodl cells that appear to help put the brain to sleep rather than simply responding to sleep onset. The work was conducted while Dr. Batista-Brito and her laboratory were based at Albert Einstein College of Medicine; she recently joined the Icahn School of Medicine, where her laboratory continues to investigate how cortical circuits regulate sleep and behavioral state.
"The traditional view of the cortex is as a passive follower during sleep," said Dr. Batista-Brito, senior author of the paper. "What we found is that the cortex itself contains circuits that can actively drive and synchronize the activity associated with sleep and, when activated, can actually promote sleep."
An Exceptionally Sparse but Far-Reaching Population
Sst-Chodl neurons (搜索) are extraordinarily rare, accounting for roughly 0.2% of neurons in the cortex. Unlike most inhibitory neurons, which primarily communicate with nearby cells, these cells send signals across long distances. That architecture gives the small population the potential to influence activity across large areas of the cortex.
The research team observed that when mice were awake and alert, Sst-Chodl neurons (搜索) were largely quiet. As the animals became drowsy and entered deep non-rapid eye movement (NREM) sleep—the quiet, restful phase characterized by slowed breathing, reduced muscle activity, and distinct brain-wave patterns—the cells became active as the cortex shifted into the slow, synchronized rhythms characteristic of sleep.
To determine whether the neurons were merely following the brain into sleep or helping take it there, the researchers activated them directly. Electrical signals across the neocortex became slower and more synchronized, resembling the cortical activity characteristic of sleep. The manipulation was also sufficient to promote sleep, causing mice to fall asleep more readily and spend more time sleeping.
"These neurons don't simply become active when the animal sleeps," Dr. Batista-Brito said. "They can actually help drive the transition toward sleep."
Evolutionary Conservation Points to a Fundamental Role
Despite their scarcity, Sst-Chodl neurons (搜索) have been preserved across hundreds of millions of years of evolution, from amphibians and reptiles to humans.
"Evolution has held onto these cells for an incredibly long time, even though there are very few of them," Dr. Batista-Brito said. "That suggests they are doing something important. Until now, we knew surprisingly little about what that was."
The study, conducted in mice, establishes the role of these neurons in cortical synchronization and sleep. Their extraordinary evolutionary conservation raises the possibility that they perform a similarly fundamental function in other animals, potentially including humans.
Testing Whether the Cortex Senses Sleep Pressure
The discovery raised a further question: whether Sst-Chodl neurons (搜索) help translate the brain's need for sleep into sleep itself.
"As we stay awake, sleep pressure builds until eventually the brain has to sleep," Dr. Batista-Brito said. "One possibility we are interested in investigating is whether these neurons help sense or enforce that need, pushing the cortex toward sleep when we become too tired. We don't know that yet—but it is an exciting hypothesis we plan to test."
Implications for Sleep Disruption in Disease
Sleep is disrupted in many neurological, neurodevelopmental, and psychiatric disorders, including Alzheimer's disease (搜索) and autism spectrum disorder (搜索). The identification of a specific cortical circuit now allows researchers to ask whether these ancient neurons are altered when normal sleep breaks down.
"Are these neurons functioning normally when sleep becomes disrupted? Could changes in this system contribute to sleep problems in disease?" Dr. Batista-Brito posited. "We don't know yet, but now we have a specific circuit to investigate."
Taken together, the results point toward a broader shift in how scientists conceptualize sleep: rather than being controlled only by specialized centers deep within the brain, sleep may emerge from an interaction between those systems and the cortex itself.