August 13, 2015

A new Israeli-led study based on rare neuronal data offers the first scientific evidence of the link between rapid eye movement (REM) sleep- the period in which we experience vivid dreams- dream images, and accelerated brain activity.

According to the study, when we move our eyes in REM sleep specific brain regions show sudden surges of activity that resemble the pattern that occurs when we see new images when awake. The scientists suggest that these flickering eye movements during REM sleep are responsible for resetting our dream “snapshots” or “changing the scene” in our dreams.

“The electrical brain activity during rapid eye movements in sleep were highly similar to those occurring when people were presented with new images,” said by Dr. Yuval Nir of Tel Aviv University’s Sackler Faculty of Medicine, who led the study. “Many neurons — including those in the hippocampus — showed a sudden burst of activity shortly after eye movements in sleep, typically observed when these cells are ‘busy’ processing new images.”

“The research findings suggest that rapid eye movements represent the moment the brain encounters a new image in a dream, similar to the brain activity exhibited when one encounters visual images while awake,” said TAU’s Prof. Itzhak Fried, also of UCLA and Tel Aviv Medical Center.

The research, recently published in Nature Communications, was a collaboration between TAU’s Fried and Nir and Thomas Andrillon of the Laboratoire de Sciences Cognitives et Psycholinguistique in Paris; and Dr. Giulio Tononi and Dr. Chiara Cirelli of the University of Wisconsin-Madison.

The recordings were made from 19 patients with electrodes implanted in their brains to monitor epileptic seizures. These electrodes were able to provide the rare data needed to prove the link between eye movements, dream imagery, and brain activity.

“We focused on the electrical activities of individual neurons in the medial temporal lobe, a set of brain regions that serve as a bridge between visual recognition and memories,” said Dr. Nir. “Prof. Fried’s prior research had shown that neurons in these regions become active shortly after we view pictures of famous people and places, such as Jennifer Aniston or the Eiffel Tower — even when we close our eyes and imagine these concepts.”

In addition to monitoring the patients’ brain activity via intracranial electrodes, the researchers also recorded scalp EEG, muscle tone, and eye movements to identify periods of REM sleep and detect the precise moment of each rapid eye movement.

“How and why eye movements occur are important,” said Dr. Nir. “And these moments represent privileged windows of opportunity for the study of brain activity.”

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