Reasons of shift from deep sleep to lighter one

Turns out, there is a logical reason behind the sudden shift to light sleep from a deep sleep over the course of a night.

According to a study conducted by the Bar-Ilan University, brief arousals are probably triggered by the intrinsic electrical noise from wake-promoting neurons (WPN) in the brain.

The research revealed a previously unrecognised neurophysiological mechanism that links sleep arousals with temperature regulation, and may also provide an important new link between temperature and Sudden Infant Death Syndrome (SIDS).

During sleep, WPN is suppressed by sleep-promoting neurons. Nevertheless, Hila Dvir, lead co-author of the study, surmised that WPN still maintains a low level of activity, in the form of noise ("neuronal noise").

Neuronal noise is very much affected by body temperature, so if the temperature is high, neuronal noise is low and vice versa.

The findings of the study presented a possible new link between temperature, sleep arousals and Sudden Infant Death Syndrome (SIDS), the sudden, unexplained death during sleep of children under one year of age.

Elevated room temperature, extensive crib bedding and prone sleeping position - all factors that contribute to higher body temperature - are known to increase the risk of SIDS. So far, the mechanism of why higher body temperature increases the risk of SIDS is unknown but neuronal noise and brief arousals could be a key.

Since thermoregulation in young infants is not yet fully developed, their body temperature is highly affected by the environment/room temperature (similar to fish). "We think that SIDS can occur when as a result of higher temperature, neuronal noise levels and the associated probability for arousals are low," said Dvir.

"In contrast, when the temperature is lower, an infant has a higher neuronal noise level that yields more arousals during which the infant can change his position to help himself breath more freely or move a blanket that may be covering his face."

The study appears in the journal Science Advances.