Ever sleep poorly and then walk out of the house without your keys? Or space out while driving to work and nearly hit a stalled car?

A new study led by UCLA’s Dr. Itzhak Fried is the first to reveal how sleep deprivation disrupts brain cells’ ability to communicate with each other. Fried and his colleagues believe that disruption leads to temporary mental lapses that affect memory and visual perception. Their findings are published online today by Nature Medicine.

“We discovered that starving the body of sleep also robs neurons of the ability to function properly,” said Fried, the study’s senior author, a professor of neurosurgery at the David Geffen School of Medicine at UCLA and Tel Aviv University. “This leads to cognitive lapses in how we perceive and react to the world around us.”

UCLA Health Dr. Itzhak Fried

The international team of scientists studied 12 people who were preparing to undergo surgery at UCLA for epilepsy. The patients had electrodes implanted in their brains in order to pinpoint the origin of their seizures prior to surgery. Because lack of sleep can provoke seizures, patients stay awake all night to speed the onset of an epileptic episode and shorten their hospital stay.

Researchers asked each study participant to categorize a variety of images as quickly as possible. The electrodes recorded the firing of a total of nearly 1,500 brain cells (from all of the participants combined) as the patients responded, and the scientists paid particular attention to neurons in the temporal lobe, which regulates visual perception and memory.

Performing the task grew more challenging as the patients grew sleepier. As the patients slowed down, their brain cells did, too.

“We were fascinated to observe how sleep deprivation dampened brain cell activity,” said lead author Yuval Nir of Tel Aviv University. “Unlike the usual rapid reaction, the neurons responded slowly and fired more weakly, and their transmissions dragged on longer than usual.”

Lack of sleep interfered with the neurons’ ability to encode information and translate visual input into conscious thought.

The same phenomenon can occur when a sleep-deprived driver notices a pedestrian stepping in front of his car.

“The very act of seeing the pedestrian slows down in the driver’s overtired brain,” Fried said. “It takes longer for his brain to register what he’s perceiving.”

The researchers also discovered that slower brain waves accompanied sluggish cellular activity in the temporal lobe and other parts of the brain.

“Slow, sleep-like waves disrupted the patients’ brain activity and performance of tasks,” Fried said. “This phenomenon suggests that select regions of the patients’ brains were dozing, causing mental lapses, while the rest of the brain was awake and running as usual.”

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The study’s findings raise questions about how society views sleep deprivation.

“Severe fatigue exerts a similar influence on the brain to drinking too much,” Fried said. “Yet no legal or medical standards exist for identifying overtired drivers on the road the same way we target drunk drivers.”

In future research, Fried and his colleagues plan to more deeply explore the benefits of sleep, and to unravel the mechanism responsible for the cellular glitches that precede mental lapses.

Previous studies have tied sleep deprivation to a heightened risk of depression, obesity, diabetes, heart attacks and stroke. Research has also shown that medical school residents who work long shifts without sleep are more prone to make errors in patient care.

The research was supported by the National Institute of Neurological Disorders and Stroke, the National Institute of Mental Health, the Human Frontier Science Program Organization, the Israel Science Foundation, the Marie Curie Career Integration Grant, the Adelis Foundation and the French Operations Research and Decision Support Society.

The paper’s other coauthors were Thomas Andrillon of the École Normale Supérieure in Paris; Amit Marmelshtein of Tel Aviv University; Nanthia Suthana of UCLA; and Guilio Tononi and Chiara Cirelli of the University of Wisconsin, Madison.

Learn more about the neuroscience research theme at UCLA.