Here’s how sleep manifests in the brain The waves slowly surge They move across the surface at a rate of about one every tenth of a second — or at least that’s what we thought.
A new study in mice suggests that there are previously overlooked patterns of sleep-related brain activity that reflect the state of individual brain cells rather than the collective activity of millions or billions of neurons.
Moreover, by using single-wire electrodes to measure these hyperlocal, sub-millimeter brain signals, the researchers found that parts of the mammalian brain can go into a brief state of nap while other regions remain fully awake.
“It was a surprise for us as scientists to discover that another part of the brain actually takes a little nap while the other part of the brain is awake.” To tell David Hausler, a bioinformatics researcher at the University of California, Santa Cruz, and lead author of the study.
For nearly a century, patterns of electrical activity throughout the brain have been used to quantitatively define the difference between sleep and wakefulness. These EEG signals are Electroencephalogram (Electroencephalogram) Measurements are taken by attaching electrodes to the scalp.
But Hausler and his team questioned how sleep has been measured and distinguished from wakefulness. There is clearly some crossover in the brains of animals that remain awake while they sleep, which may explain why some researchers believe that sleep is the most important neurotransmitter. Unihemispheric slow wave sleep.
In the 1960s, researchers first suspected and then discovered the cause. Dolphins and other cetaceans They are able to rest one half of their brain while still being active, and sometimes even keep one eye open to watch for predators and stay in contact with the rest of the herd.
Seals and birds also exhibit variations of this half-asleep, half-awake rest, a clever trade-off between sleep and survival.
Humans can briefly exhibit asymmetric sleep patterns that are reminiscent of, but not identical to, those seen in animals.
In 2016, researchers at Brown University in the US found that the first night people sleep in a strange place, the left brain is more active. Be more alert to unusual sounds As you get used to your sleeping environment, this difference will decrease.
“It turns out that the human brain has a less dramatic form of hemispheric sleep than is seen in birds and some mammals,” says neuroscientist Christof Koch. I have written in Scientific American When the results are published.
Looking at the mouse brain, the blurred distinction between wakefulness and sleep in humans may ultimately be a neurological feature we share with other animals.
Hausler and his team collected data over several weeks from nine mice with thin electrodes implanted in 10 different parts of the brain, and fed the data into an artificial neural network that learned to distinguish between sleep and wakefulness.
Records were sampled from 100 micrometers (tenths of a metre). Millimeters), the algorithm was able to reliably identify sleep-wake cycles based on short ‘flickers’ of brain cell activity lasting just 10-100 milliseconds.
These “hyperlocal” signals suggest that parts of the mouse brain are dozing off, while other parts remain active and awake. Coincidentally, the researchers noticed this happening at the very moment the mice stopped moving, as if they were “dazed.”
“If you look at the time each of these neurons fires individually, [the neurons] It was moving to another state.” explain Aiden Schneider, a computational biologist at Washington University in St. Louis, co-led the study with David Parks, a computer science graduate student at the University of California, Santa Cruz.
“In some cases, these flickers can be localized to specific areas of the brain and even smaller than that.”
The team believes that if this ‘flickering’ is observed by other groups, new ways of measuring sleep-wake states could reveal new secrets about how we sleep.
“They are [the flickers] It breaks the rules that are expected based on 100 years of literature.” To tell Keith Hengen, a neuroscientist at Washington University in St. Louis.
This study Nature Neuroscience.
