Scientists from the Chinese Academy of Sciences’ Shenzhen Institute of Advanced Technology (SIAT) found that a common circuit regulates rapid eye movement (REM) sleep and innate fear.
For years, scientists have speculated that REM sleep helps animals prepare for attacks by exciting a flight or fight response. This causes them to wake up briefly after short periods.
Scientists proposed the theory in 1966
Dr. Frederic Synder first suggested this theory in 1966. Despite its popularity, there has been little evidence to support his claims. This new study changes that.
The researchers put animals to sleep in a steel chamber where they exposed them to a trimethylthiazoline (TMT) odor. This smell can stimulate an animal into thinking there is a predator present.
The team found that the odor caused the animals to get up from REM sleep. However, this was not the same response with non-REM sleep. They concluded that the characteristics of REM sleep enabled the animals to wake up quickly.
The researchers monitored the medial subthalamic nucleus
After concluding that REM sleep had higher arousal thresholds than non-REM sleep, the researchers tried to find out what caused this. They looked into the medial subthalamic nucleus (mSTN), an area of the brain with a high concentration of neurons that secrete a corticotrophin-releasing hormone (CRH).
The researchers used cell-type particular manipulations and recorded neural activity and found that mSTN-CRH neurons caused a low arousal threshold during REM sleep. Moreover, they increased defensive actions after people woke up.
Researchers also concluded that increased exposure to predators increased REM sleep. However, it also caused sleep architecture fragmentation and a shorter duration of REM sleep. Experts call this period desynchronized or paradoxical sleep. This name is due to differences in the waking states.
Additionally, the team thinks that the chemical and electrical activities regulating REM sleep come from the brain. Both monoamine transmitters and neurotransmitters also impact them.
These findings show the role evolution plays in our sleep. Moreover, it describes the chemical activities involved in REM sleep. The team now wants to investigate if they could treat mood disorders by targeting sleep and fear mechanisms.
