“Mah rabu maasecha Hashem, kulam b’chochmah asisa” — “How great are Your works, Hashem; You made them all with wisdom.” (Tehillim 104:24)

By Rabbi Yair Hoffman

Every night, when we close our eyes and drift off to sleep, something remarkable happens inside our brains — something so intricate and so perfectly designed that scientists are only now beginning to understand it. A recent study published in the prestigious journal PNAS (March 2026) has uncovered a stunning system of coordination in the sleeping brain that should fill every thinking person with a deep sense of yiras Shamayim.

The Rambam in Hilchos Deos 4:4 explains that ideally we should be sleeping 8 hours a night.  Researchers from the University of Oulu in Finland may provide for us another reason for this Rambam. They studied 24 healthy volunteers while they were both awake and asleep. Using three different high-tech instruments simultaneously — a special ultra-fast MRI machine, a 256-electrode brainwave monitor (EEG), and an infrared light sensor — they watched what happens inside the living human brain as it transitions from wakefulness into sleep.

The researchers were simultaneously tracking three separate systems inside the brain: blood flow (how oxygen-rich blood pulses through the brain), electrical activity (the brain’s own electrical signals), and water movement — specifically cerebrospinal fluid, the clear liquid that bathes and protects the brain. What they found was pure unmitigated  Niflaos HaBorei.

Two Different Modes — Perfectly Designed

During wakefulness, the brain runs in one mode. The electrical signals fire first, and the blood flow follows. It is like a foreman giving orders to workers: the neurons call out, and the blood vessels respond by delivering more oxygen. Scientists call this “neurovascular coupling,” and it is the classical understanding of how the brain operates. The water movement also follows along in this same orderly chain of command.

The moment a person falls asleep, the entire system reorganizes itself — automatically, without any conscious effort — into a completely different mode of operation.

During sleep, the three systems begin talking to each other in both directions simultaneously. Instead of a simple one-way command structure, the blood flow, the electrical signals, and the fluid movement all begin influencing each other in a beautifully coordinated, bidirectional dance. The researchers measured this using a sophisticated mathematical tool called “phase transfer entropy,” which can detect which signal is “predicting” or “leading” another.

The Brain Cleans Itself While You Sleep

And now more niflaos HaBorei. The brain accumulates waste products during the day — toxic proteins and metabolic byproducts that, if left to build up, can cause serious damage. Scientists have discovered in recent years that the brain has its own cleansing system, called the glymphatic system, which flushes these waste products out.

And this cleaning system runs primarily during sleep.

The slow, rhythmic waves of cerebrospinal fluid that increase during sleep — driven by a molecule called norepinephrine that oscillates at a slow rhythm of about once every 50 seconds — are what power this cleaning process. The brain’s blood vessels pulse slowly and powerfully during sleep, and like a gentle pump, they push the cleansing fluid through the narrow spaces between brain cells, washing out the accumulated toxins.

The researchers found that during sleep, these slow waves increase dramatically in power — more than doubling in some measurements. The speed at which these waves travel through the brain also increases during sleep, particularly in the sensory and motor areas of the brain. The entire system accelerates its cleaning operation precisely when the brain is not busy processing the outside world.

“Hareini oheiv otcha b’chol libi” — the Creator embedded within us systems of self-repair and renewal that operate even while we are entirely unaware.

Norepinephrine: The Master Conductor

One of the most striking findings is the role of a single molecule — norepinephrine (NE) — as the conductor of this entire symphony. During sleep, norepinephrine levels drop and then oscillate slowly. These oscillations trigger the vasomotor waves. But remarkably, this same molecule has opposite effects on two neighboring cell types:

• In neurons (nerve cells), declining norepinephrine increases a certain ion pump’s activity
• In astrocytes (support cells that surround blood vessels), declining norepinephrine decreases that same pump’s activity

These opposing effects create an electrical pressure difference between the two cell types — and that pressure difference is what drives the cerebrospinal fluid to flow through the brain’s interstitial spaces, carrying away the waste.

One molecule. Two opposite effects on neighboring cells. A perfectly engineered pressure system that cleans the brain.

“Nishmas kol chai t’varech es shimcha” — the very breath of every living creature praises Your Name — because even in unconscious sleep, the intricate machinery of life declares the glory of its Maker.

What Happens When Sleep Is Disrupted?

The implications of this research are sobering. When a person does not sleep enough, this entire cleaning system is compromised. Earlier research cited in this study showed that disrupting slow-wave sleep actually increases the levels of amyloid-beta — the toxic protein associated with Alzheimer’s disease — in the cerebrospinal fluid. The brain’s nightly maintenance crew cannot complete its work.

This gives new scientific weight to the Torah’s vision of the human body as a pikadon — a precious deposit entrusted to our care. Neglecting sleep is not merely a lifestyle choice. It interferes with a magnificent system that the Creator built into us for our protection and maintenance.

The Bigger Picture

What makes this study so significant is that it reveals a level of design that no engineer could have conceived. How so? This is what was discovered that is happening simultaneously during sleep:

1. Norepinephrine levels oscillate at precisely the right frequency
2. Blood vessels pulse in response, creating pressure waves
3. Cerebrospinal fluid moves in the opposite direction of the blood
4. Astrocyte cells physically change their shape — swelling and shrinking — to open pathways for fluid flow
5. The electrical activity of the brain shifts to complement all of this
6. The entire system becomes bidirectional and self-reinforcing

All of this happens automatically, every single night, in every human being, without any conscious instruction or effort.

The Ramban writes that the human body itself is evidence of the Divine, because its complexity surpasses all human understanding. This study, conducted with some of the most advanced brain imaging technology in existence, has only deepened that truth.

Mah rabu maasecha Hashem — how great are Your works, Hashem. You made them all with wisdom.

The author can be reached at [email protected]

The original study, “Sleep Alters Neurovascular and Hydrodynamic Coupling in the Human Brain,” was published in PNAS, Vol. 123, No. 12 (March 18, 2026) by Väyrynen et al., University of Oulu, Finland.