Under the Hood

Here's How High Body Temperature Puts Infants At Risk Of Sudden Death

Sudden infant death syndrome (SIDS) is among the top five causes of death for infants in the United States. While experts have outlined certain risk factors and guidelines, the exact cause of SIDS has not been understood. But newly published research on sleep arousals may hold answers.

The study was a collaboration between scientists from Boston University in the U.S. and Bar-Ilan University in Israel. The paper titled "Neuronal noise as an origin of sleep arousals and its role in sudden infant death syndrome" was published in the journal Science Advances on April 25. 

What is sleep arousal? How does it occur?

Arousal does not mean the child wakes up, but rather "transitions from deep sleep to a mixture of very light sleep and/or partial wakefulness," as stated by Stanford Health Care. The new study identified that wake-promoting neurons (WPN) may trigger these brief arousals by causing an electrical noise of sorts in the brain.

While WPN are suppressed by sleep-promoting neurons during sleep, they still maintain a low level of activity in the form of "neuronal noise." When this noise has accumulated to a significant degree, it can form a strong enough signal to activate WPN and cause a brief arousal.

What kind of experiment did the scientists conduct?

The research team discovered a previously unrecognized neurophysiological mechanism which linked sleep arousals with temperature regulation. When the body temperature is high, the neuronal noise is low and vice versa. Keeping this in mind, the scientists decided to test whether the temperature dependence of neuronal noise could change the arousal behavior in zebrafish.

Zebrafish were chosen for the experiment since their body temperature can be easily manipulated by changing the temperature of the water they reside in. After being analyzed during periods of sleep and varying water temperatures, it was found that an increase in water temperature led to fewer and shorter arousals.

"Because of this excellent agreement between model predictions and the experiment, we believe that sleep arousals can be attributed to the neuronal noise of wake-promoting neurons," confirmed co-author Dr. Ronny Bartsch, a professor from Bar-Ilan's Department of Physics.

But what does this have to do with SIDS?

Guidelines to prevent SIDS often state that the following should be avoided: the use of bedding, elevated room temperature, and the prone sleeping position. All these factors also contribute to higher body temperature. While the link was not understood before, the new findings suggest that neuronal noise and brief arousals could be the reason why higher body temperatures increase the risk of SIDS.

In other words, a high body temperate can lead to low neuronal noise, thus reducing the possibility for arousals.

"In contrast, when the temperature is lower, an infant has higher neuronal noise level that yield 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," said lead co-author Dr. Hila Dvir, a professor from Bar-Ilan's Department of Physics.