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After a sleepless night, you likely feel sluggish the next morning, and a small new study suggests why: Your brain cells feel sluggish, too. And when those brain cells are tired, you may be more likely to be forgetful and get distracted more easily, the research found.

In the study, the researchers found that sleep deprivation makes it difficult for brain cells to communicate effectively, which, in turn, can lead to temporary mental lapses that affect memory and visual perception.

In other words, the findings offer clues as to why a sleepless night makes it so hard to think and concentrate the next day.

"We discovered that starving the body of sleep also robs neurons of the ability to function properly," senior study author Dr. Itzhak Fried, a professor of neurosurgery at the University of California, Los Angeles (UCLA), said in a statement. "This paves the way for cognitive lapses in how we perceive and react to the world around us."

To study the effects of sleep deprivation, the researchers recruited 12 patients with epilepsy who, as part of a preparation for surgery unrelated to the study, had electrodes implanted into their brains.These electrodes allowed the researchers to monitor hundreds of individual brain cells.

The people in the study then had to stay up for an entire night. During this time, the researchers measured the participants' brain activity as they carried out certain tasks. For example, the patients were asked to categorize various images of faces, places and animals as fast as possible. Each image caused cells in areas of the brain to produce distinctive patterns of electrical activity. Specifically, the researchers focused on cell activity in the temporal lobe, which regulates visual perception and memory.

The researchers found that as the patients got tired, it became more challenging for them to categorize the images, and their brain cells began to slow down.

"We were fascinated to observe how sleep deprivation dampened brain cell activity," lead study author Yuval Nir, a sleep researcher at Tel Aviv University in Israel, said in the statement. "Unlike the usual rapid reaction, the neurons responded slowly, fired more weakly and their transmissions dragged on longer than usual."

In addition, the researchers found that sleep deprivation affects some areas of the brain more than others. Regions of the brain that experienced sluggish brain cell activity also exhibited brain activity normally seen when a person is asleep, the researchers 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," Fried said.

In addition, the findings suggest that a lack of sleep can interfere with the ability of neurons in the brain to encode information and translate visual input into conscious thought, the researchers said. For example, when a sleep-deprived driver sees a pedestrian stepping in front of his car, it may take longer for the driver to realize what he or she is seeing because "the very act of seeing the pedestrian slows down in the driver's overtired brain," Nir said.

The researchers compared the effects of sleep deprivation to those of drunk driving.

"Inadequate sleep exerts a similar influence on our brain as 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."

The study was published yesterday (Nov. 6) in the journal Nature Medicine.