Brain regions can take short naps during wakefulness, leading to errors

April 27, 2011
A photo of rats with objects introduced into their cages to keep them awake. Credit: Giulio Tononi, M.D., Ph.D., University of Wisconsin-Madison

If you've ever lost your keys or stuck the milk in the cupboard and the cereal in the refrigerator, you may have been the victim of a tired brain region that was taking a quick nap.

Researchers at the University of Wisconsin-Madison have a new explanation. They've found that some in a sleep-deprived yet awake brain can briefly go "off line," into a sleep-like state, while the rest of the brain appears awake.

"Even before you feel fatigued, there are signs in the brain that you should stop certain activities that may require ," says Dr. Chiara Cirelli, professor of psychiatry at the School of Medicine and Public Health. "Specific groups of may be falling asleep, with negative consequences on performance."

Until now, scientists thought that generally affected the entire brain. Electroencephalograms (EEGs) show network brain-wave patterns typical of either being asleep or awake.

"We know that when we are sleepy, we make mistakes, our attention wanders and our vigilance goes down," says Cirelli. "We have seen with EEGs that even while we are awake, we can experience shorts periods of 'micro sleep.' "

Periods of micro sleep were thought to be the most likely cause of people falling asleep at the wheel while driving, Cirelli says.

But the new research found that even before that stage, brains are already showing sleep-like activity that impairs them, she says.


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As reported in the current issue of Nature, the researchers inserted probes into specific groups of neurons in the brains of freely-behaving rats. After the rats were kept awake for prolonged periods, the probes showed areas of "local sleep" despite the animals' appearance of being awake and active.

"Even when some neurons went off line, the overall measurements of the indicated in the rats," Cirelli says.

And there were behavioral consequences to the local sleep episodes.

"When we prolonged the awake period, we saw the rats start to make mistakes," Cirelli says.

When animals were challenged to do a tricky task, such as reaching with one paw to get a sugar pellet, they began to drop the pellets or miss in reaching for them, indicating that a few neurons might have gone off line.

"This activity happened in few cells," Cirelli adds. "For instance, out of 20 neurons we monitored in one experiment, 18 stayed awake. From the other two, there were signs of sleep—brief periods of activity alternating with periods of silence."

The researchers tested only motor tasks, so they concluded from this study that neurons affected by local sleep are in the motor cortex.

More information: Local sleep in awake rats. Vyazovskiy VV, Olcese U, Hanlon EC, Nir Y, Cirelli C, Tononi G. Nature. 2011 April 28.

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5 comments

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mjesfahani
1 / 5 (1) Apr 28, 2011
amazing, really iam amazed. When you are driving does it take rest too?
Vendicar_Decarian
1 / 5 (1) Apr 28, 2011
This isn't surprising.

We know that sleep is triggered by a chemical "sleep factor", and it is reasonable to presume that not all neurons are going to be exactly tuned to the same concentration of this sleep factor.

So the ones that are most sensitive, are triggered first. They metabolize the sleep factor and become awake again, and should fall asleep as the sleep factor molecules continue to slowly bind to the sensing proteins.

A good proof of this model would be to show that it is the same neurons that are triggered first in each instance, since this would indicate their chemical sensitivity.

Neural nets are somewhat immune to point defects so would continue to perform - although subnormally - even with some neurons non-functional.

cyberCMDR
not rated yet Apr 30, 2011
How much of Donald Trump's brain is asleep?
George_Rodart
not rated yet May 04, 2011
I forgot what I was going to say, but I gave it a 5.
Megadeth312
not rated yet May 08, 2011
We know that sleep is triggered by a chemical "sleep factor", and it is reasonable to presume that not all neurons are going to be exactly tuned to the same concentration of this sleep factor.


The neurotransmitter that you are referring to is known as "Adenosine". It is more likely that neuronal activity suppresses the effects of the neurotransmitter, meaning that parts of the brain that are not directly in use have a chance to fall asleep, rather than some of them being more or less sensitive to the chemical signal. Sleep deprivation studies have shown that while it becomes less effective, and may cause psychological issues, the human brain can technically stay awake indefinitely.

This is rather unsurprising however, when you consider whales and dolphins are able to allow one half of the brain to sleep while the other stays awake.

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