We spend nearly a third of our lives sleeping, yet the biological trigger behind sleep has remained elusive. Despite decades of research, scientists have struggled to identify a concrete, physical reason why the brain demands rest.
A new study from the University of Oxford might have changed that.
Researchers have found that the pressure to sleep may come from deep inside our brain cells, from the tiny power plants known as mitochondria. These structures, responsible for converting oxygen into energy, appear to sound an internal alarm when pushed into overdrive.
The team, led by Professor Gero Miesenböck and Dr. Raffaele Sarnataro, discovered that a build-up of electrical stress inside mitochondria in specific brain cells acts as a signal to trigger sleep.
The research, carried out in fruit flies, showed that when mitochondria become overcharged, they leak electrons.
“When they do, they generate reactive molecules that damage cells,” said Dr. Sarnataro.
This electron leak produces what are known as reactive oxygen species, byproducts that, in high quantities, can damage cellular structures.
The brain appears to respond to this imbalance by initiating sleep, giving the cells a chance to reset before damage spreads further. The findings open a new chapter in how scientists think about energy metabolism’s role in brain health.
Switch in the brain
The researchers found that specialized neurons function like circuit breakers. These cells measure the electron leak and trip the sleep response when the stress crosses a threshold.
By manipulating the energy flow in these neurons, either by increasing or decreasing electron transfer, the scientists could directly control how long the flies slept.
They even bypassed the system’s normal inputs by replacing electrons with energy from light using microbial proteins. The result remained the same: more energy, more leak, more sleep.
“We set out to understand what sleep is for, and why we feel the need to sleep at all,” said Professor Miesenböck.
“Our findings show that the answer may lie in the very process that fuels our bodies: aerobic metabolism.”
He explained that when the mitochondria in certain sleep-regulating neurons are overloaded with energy, they begin leaking electrons.
When this leak becomes too great, the neurons trigger sleep to prevent damage from escalating.
Ties to aging and fatigue
The findings may help explain why metabolism and sleep are so closely linked. Small animals that consume more oxygen per gram of body weight tend to sleep more and live shorter lives.
Meanwhile, people with mitochondrial disorders often experience extreme fatigue even without physical exertion. This new mechanism offers a potential explanation.
“This research answers one of biology’s big mysteries,” said Dr. Sarnataro. “Why do we need sleep? The answer appears to be written into the very way our cells convert oxygen into energy.”
These insights could reshape not just sleep science, but also how doctors understand chronic fatigue, neurological disorders, and the aging process itself.
The study is published in the journal Nature.
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