Fatigue slows down brain cell activity

A new international study, led by researchers from Tel Aviv University, found that sleep patterns "invade" certain areas of the waking brain - results that in the future could be used as a basis for road fatigue "owls"

In a new study, researchers from Tel Aviv University, the University of California at Los Angeles (UCLA) and the University of Wisconsin found that the nerve cells themselves slow down their responses during fatigue or sleep deprivation.

The unique study, the results of which were published on Monday (6.11) in the journal Nature Medicine, is the product of an international collaboration led by Dr. Yuval Nir from the Sackler Faculty of Medicine, the Purple School of Neuroscience at Tel Aviv University and the Sourasky Medical Center Tel Aviv, and Prof. Yitzhak Fried from UCLA, the Sackler Faculty of Medicine at Tel Aviv University Aviv and Sourasky Tel Aviv Medical Center, in collaboration with sleep researchers Prof. Chiara Cirelli and Giulio Tononi from the University of Wisconsin-Madison, research student Amit Marmelstein from the Segol School of Neuroscience at Tel Aviv University and other research teams in Paris and UCLA.

"Recent surveys indicate that more than 20% of traffic accidents are related to driving fatigue, and 28% of drivers reported actually falling asleep while driving in the last year," explains Dr. Nir. "During sleep deprivation, we often fail to respond effectively to what is happening around us. In certain situations, such as in the control tower or the operating room, mistakes of this type can have devastating consequences. However, until today it was not clear how sleep deprivation affects the activity of nerve cells in the brain."

"Parts of the brain fell asleep"

To test the neurological mechanism behind the impaired responses during sleep deprivation, the researchers took advantage of a rare opportunity in which epileptic patients undergo implantation of intracranial electrodes.-Cerebral, in an effort to locate the brain area that causes seizures. Twelve patients at UCLA, who were hospitalized for a week while their brain activity was recorded, volunteered for the study and in some cases stayed up all night.

The participants in the study were shown pictures of famous figures and places, and they were asked to classify the pictures as quickly as possible - in order to test their vigilance. In a series of over 30 experiments, the team of researchers recorded the electrical activity of nearly 1,500 neurons in the brain.

"The study revealed that during sleep deprivation, the subjects' reaction to the images became slower, weaker and longer than usual," explains Prof. Fried. "We were able to show that during this time, responses of individual neurons in the temporal lobe - an area linked with visual perception and memory - also changed as a result of the fatigue."

"It is important to emphasize that these tremors are not the result of micro-sleep, which is accompanied by closing the eyes, what we call 'squinting,'" adds Dr. Nir. "Here the subjects looked directly at the picture, while specific parts of their brains simply fell asleep."

The unique view of human brain activity, made possible by this study, reveals how sleep deprivation affects not only decision-making processes and muscle control, but also early processes of object recognition, perception and memory. As such, the study provides a future basis for road fatigue measurement.

"When we are tired, sleep-like brain waves 'invade' the activity of the awake brain while we perform tasks, long before we actually fall asleep, or just close our eyes," concludes Dr. Nir. "Since driving while tired is just as dangerous as driving drunk, we hope that the new study will serve as a basis for objective measurement of the intensifying waves of sleep, like the 'owls' that measure the concentration of alcohol in the blood - before this fatigue becomes life-threatening."

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