A link between rapid eye movement while dreaming and the activity of visual and memory centers in the brain during wakefulness has been proven for the first time by Tel Aviv University researchers. The study was released for publication in the prestigious journal Nature Communications.
Already in the 1950s, scientists discovered rapid eye movement, or dream, sleep, a stage in which people dream “colorful” dreams and move their pupils rapidly. But only now, six decades later, have TAU scientists managed to prove scientifically the seemingly intuitive connection between eye movements and “movies” that we see in our sleep.
The researchers were Dr. Yuval Nir of the physiology and pharmacology department in TAU’s Sackler School of Medicine and the Sagol School of Neuroscience and Prof. Itzhak Fried, a world-renowned neurosurgeon at the medical school, Tel Aviv University and at the University of California at Los Angeles. Others involved in the study were Thomas Andrillon of the Laboratoire de Sciences Cognitives et Psycholinguistique in Paris; and Drs.
Chiara Cirelli and Giulio Tononi of the psychiatry department of the University of Wisconsin-Madison.
The TAU-led research, which is being called a “breakthrough,” was based on a unique database of brain surgery in epilepsy patients. “Sometimes, when an epilepsy patient does not react to medication, doctors try to find the focus in his brain that cause the neurological attacks and to help him by removing it surgically,” they wrote in the article published on Tuesday evening.
As preparation for the operation, sensors are implanted in the brain, and the activity there is monitored for about 10 days, explained Nir. “This created a rare accumulation of data – which cannot be obtained in any other way – taken directly from the depths of the human brain. We used the data to find out what occurs in the brain during REM sleep.”
Nineteen volunteers – all epilepsy patients treated by neurosurgeon Fried in the UCLA department – participated in the study. “We asked their permission” to use the data from the brain sensors that were in any case necessary for their treatment, and they happily obliged,” said Nir. “We registered their brain activities during sleep and attached to their eyes stickers that sensed their movements to coordinate them with the brain activity.”
The researchers also presented to the awake patients pictures of familiar places and people such as the Eiffel Tower, famous people and loved ones to exactly identify the neurons that are aroused when the brain identifies a picture and remembers associations connected to it.
Fried found in previous studies that when a person closes his eyes and imagines, the same lively activity occurs in the brain as when the individual sees actual objects.
“We wanted to find out what happens in these cells, which are responsible for identifying pictures and concepts coded in the brain during REM sleep,” said Nir.
“Analyzing the data we collected raised a fascinating link between eye movements and brain activities. Every time the eyes moved, many neurons connected to identifying pictures woke up about 0.3 seconds later. In addition, the characteristics and indicators of the burst of brain activity – such as the order in awakening and intervals of time – were exactly the same as those familiar to use from watching the brain’s reaction to a real picture or suggesting a picture to one’s imagination.
In fact, it looks as if every time the eyes move, the ‘slide’ in the ‘movie’ of the dream changes.”
Thus, for the first time in more than 60 years of assumptions and trials, the link between rapid eye movement during dreams and specific brain activity representing pictures and memories was proven scientifically.
The TAU study is another step in decoding the role of dreams during sleep and in life in general, the authors said. “Studies in recent years proved that during sleep, there are brain processes that help refresh and reorganize dreams,” said Nir. “In our lab, we are looking into brain activity in various states of consciousness, when fully awake, when under anesthesia, in loss of consciousness, when tired, and of course during sleep,” he concluded.
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