BEIJING, Jan. 22 (Xinhua) -- It has been found that people roll their eyes while sleeping, an action scientists once hypothesized could help humans keep alert against predator attacks. Chinese neuroscientists have now found evidence to support the claim.

The study published on Saturday in the journal Neuron reported a common circuit that regulates both innate fear and Rapid Eye Movement (REM) sleep, a stage when one's eyes move around rapidly in a range of directions, causing people to wake up briefly and periodically.

The research team led by Wang Liping from the Shenzhen Institute of Advanced Technology of the Chinese Academy of Sciences found that a brain region capable of promoting the hormone release also regulates REM sleep.

In the experiment, the rodents slept in a sealed chamber and were exposed to an odor stimulus indicating the advent of a predator.

The odor triggered rapid arousal from REM sleep but not from non-rapid-eye-movement sleep, suggesting that REM sleep is linked to a mechanism that allows quick awakening in response to potential dangers.

Then, the researchers examined the medial subthalamic nucleus, a brain region containing a high density of neurons releasing a chemical called corticotropin.

The chemical can activate the adrenal glands to release adrenaline into the blood, which quickens the heart rate and increase blood pressure, making animals all ready for a bolt.

Also, those neurons could lower the arousal threshold during REM sleep and increase defensive responses after awakening, according to the study.

The find is an example of how evolution leads to two distinct but related functions with one tool kit in the brain, the researchers said.

"Natural selection favors optimizing existing neural circuitry for efficiency in signal transduction and energy usage over metabolically more expensive solutions," said Wang, the paper's corresponding author.

The study was supported by the co-occurrence of increased REM sleep and stress-related mood disorders found in clinical studies.

It has thus opened the possibility of treating mental disorders by targeting the common regulatory circuit of sleep and fear, according to the researchers. Enditem

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