During the Deepest Sleep, the Brain Stops Keeping Time With Your Breathing

Breathing and the brain are perpetually in conversation. During wakefulness, the two systems follow each other fairly closely - brain waves rise and fall in patterns that track the respiratory cycle. During lighter sleep, the coupling persists. But deep in non-REM sleep, something different happens: the brain, at least in certain regions, starts keeping its own time.

A Study That Went Deeper Into the Brain Than Most

A team at Hackensack Meridian Health Center for Discovery and Innovation (CDI) set out to characterize exactly how breathing and brain activity synchronize - or stop synchronizing - across different states of sleep and wakefulness. Their focus was the basal ganglia, particularly a small but important region called the substantia nigra, which controls movement and produces dopamine. The primary motor cortex was also examined.

These regions had not previously been studied in this context. The researchers measured sleep cycles in mice, recording electrical brain activity alongside breathing patterns and analyzing how the two rhythms timed off one another. They also captured data during wakefulness and under ketamine anesthesia. The study was published in The Journal of Neuroscience in January, led by Bon-Mi Gu, PhD, of CDI and the Hackensack Meridian School of Medicine.

Deep Sleep Is Where the Coupling Breaks

Across all the states measured, the team found nuances. But one consistent finding stood out: during the deepest stage of non-REM sleep, breathing was mostly independent of the brain waves, particularly the slow delta activity that defines this stage of sleep. The coupling that exists during lighter sleep or wakefulness effectively dissolves at the deepest level of slumber.

"The strength of respiration-neural coupling varied across multiple states, including NREM sleep, REM sleep, quiet wakefulness, and anesthesia, and was directly related to the delta power, a hallmark of NREM sleep," the authors wrote. The more delta power - the deeper the sleep - the less the breathing and brain activity kept pace with each other.

This decoupling has not been characterized before in these specific brain regions. "We provide the first detailed characterization of respiration-neural coupling across multiple states in the substantia nigra and the primary motor cortex, two regions not previously studied in this context," the team noted.

What This Means for Understanding Sleep - and Disease

The finding is more than a curiosity about sleep architecture. The substantia nigra is the region damaged in Parkinson disease, a condition whose early symptoms often include sleep disturbance and breathing irregularities - both of which can precede the motor symptoms that typically prompt diagnosis by years or even decades. The overlap between what this study measured and what Parkinson patients experience is not coincidental.

"Elucidating the mechanisms underlying respiration-neural coupling, especially within basal ganglia circuits, will shed light on the pathophysiology of conditions such as Parkinson disease, where both sleep and respiration are commonly disrupted," the researchers wrote. Understanding the normal coupling pattern may help researchers identify early signs of disruption in disease.

The study also has implications for anesthesia. The team measured brain-breathing coupling under ketamine as well as in natural sleep, and found distinct patterns in that state too. Better understanding of how anesthetic agents alter these coupling relationships could eventually inform how anesthesia is monitored and managed.

The research team includes Kolsoum Dehdar, PhD, and Elliot Neuberg, and recently relocated from the Neuroscience Institute at Hackensack Meridian JFK University Medical Center to CDI. The work adds to a growing body of evidence that the basal ganglia play a broader role in sleep regulation than previously appreciated.