Rare Brain Cells Can Synchronize Activity and Promote Sleep, Mouse Study Finds

A study in mice has identified a rare group of cortex neurons that can synchronize brain activity and help trigger sleep, challenging the long-held view that sleep is controlled only by structures deep in the brain. The research, led by Dr. Renata Batista-Brito of the Icahn School of Medicine at Mount Sinai and published Sept. 9 in Nature, focused on cells called Sst-Chodl neurons.

For nearly a century, scientists have treated the cortex — involved in perception, thought and memory — as a passive follower during sleep, controlled by deeper structures. Sst-Chodl neurons make up only about 0.2% of cortical neurons, but unlike most inhibitory neurons, which mainly signal nearby cells, they send connections across long distances, giving this small population the potential to influence activity across wide areas of the cortex.

The researchers found these neurons stayed largely quiet while mice were awake and alert, then became active as the animals grew drowsy and entered deep non-rapid eye movement (NREM) sleep, marked by slowed breathing and reduced muscle activity. When activated experimentally, electrical signals across the cortex grew slower and more synchronized, resembling sleep patterns, and the manipulation made mice fall asleep more readily and sleep longer.

"The traditional view of the cortex is as a passive follower during sleep," Batista-Brito said. "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." The work was done while her lab was based at Albert Einstein College of Medicine.

Sst-Chodl neurons have been evolutionarily conserved for hundreds of millions of years, appearing in amphibians and reptiles as well as humans, which researchers say suggests an important function. The study was conducted in mice, and researchers say it opens a new avenue for investigating whether these neurons are altered in sleep disorders linked to conditions such as Alzheimer's disease and autism spectrum disorder.