A new study by Bar-Ilan University researchers could shed light on the brain mechanisms behind sudden infant death syndrome, or “crib death,” when healthy infants suddenly die in their sleep.
The research, which was published this week in the journal Science Advances, is the work of physicists and sleep researchers, and is based on experiments on zebrafish and computer simulations of neuronal activity.
The researchers say the explanation for crib death can be found in what they call “neuronal noise,” a phenomenon in brain cells. Neuronal noise is the random change in nerve voltage and stems from the opening and closing of ionic channels – the channels responsible for the nerves’ voltage.
Neuronal noise is always present, both in sleep and wakefulness, and is especially sensitive to temperature. One characteristic that has been linked to crib death is a rise in the baby’s temperature because of overdressing or the overheating of the room.
“The first question that we tried to examine in the study doesn’t touch directly on crib death but on a more basic phenomenon,” said study leader Hila Dvir of Bar-Ilan University’s Physics Department. “During sleep each of us experiences short spontaneous arousals that last up to a minute, that we’re not aware of and don’t remember. We wanted to know what caused those arousals.”
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According to Dvir, scientists once thought these arousals stemmed from outside disturbances during sleep. More recent studies rejected this but could not suggest an explanation. The Bar-Ilan study argues that neuronal noise is behind these arousals and crib death.
“When neuronal noise increases in several groups of cells at the same time during sleep, it produces a signal that causes these arousals,” Dvir said. “The hypothesis is that this mechanism is a type of evolutionary survival tool designed to maintain minimal contact with the environment even during sleep, and the arousals that result help the body overcome disturbances like breathing disruptions.”
According to the study, if body temperature rises, neuronal noise is reduced, and arousals also decrease. The researchers suggest that decreased neuronal noise in infants prevents them from overcoming breathing difficulties during sleep.
No one had ever examined the connection between neuronal noise and short arousals or crib death. “While sleep processes are well known, the mechanism of short arousals remained an unsolved riddle,” Dvir said.
To test this hypothesis, Dvir and her colleagues – Prof. Shlomo Havlin, Dr. Ronny Bartsch and Prof. Plamen Ivanov of Boston University – decided to conduct simulations of arousals in the presence of neuronal noise at different temperatures. The researchers also conducted experiments on zebrafish with Prof. Lior Appelbaum and Dr. Idan Elbaz of Bar-Ilan’s Life Sciences Faculty.
The scientists studied the zebrafish as they slept, with particular attention to their arousals, at different water temperatures. The findings corresponded to the scientists’ computer simulations and showed that as water temperature rose, the number of arousals was lower, while lower temperatures increased the number of arousals.
As Dvir explained it, “Zebrafish are a good tool for checking the effect of temperature because they’re ectothermic [cold-blooded] creatures whose body temperature is identical to the environmental temperature. Humans are, of course, endotherms – with a temperature regulation system that maintains body temperature at 37 degrees Celsius. But in preemies and infants this regulation system is not yet fully developed and its characteristics resemble those of the zebrafish.”
Dvir suggests that the link between body temperature and nerve activity during sleep explains the mechanism of crib death. While more research is needed, the researchers hope that the discovery of this connection will lead to the development of new sleep drugs and drugs that could prevent crib death by increasing a baby’s neuronal noise.