Check your phone at night does not affect your biological clock

It is not uncommon for people who get up in the middle of the night to check the time or notifications of their smartphone. Many people complain that this sudden explosion of light often makes it difficult to go back to sleep. However, a new study by researchers at Northwestern University found that this phenomenon did not affect the circadian rhythm.

The new study entitled "Distinct subpopulations of ipRGC attenuate the acute and circadian effects of light on body temperature and sleep" was published in the latest issue of the journal eLife.

Kakoki | Shutterstock

The sharp bursts of light from smartphones in dark rooms are called brief pulses of light. For the study, researchers examined the effects of these light pulses on the brain and their effects on sleep. They noted that separate parts of the brain are responsible for signal processing for brief pulses of light and long exposures to light.

The lead investigator of this study, Tiffany Schmidt, explained that it was previously thought that all light signals reaching the brain through the eyes are treated only by the suprachiasmatic nucleus (RCS) of the brain, which is also responsible for the sleep-wake cycle. circadian circulation. rhythm of the brain.

Before the widespread use of electricity, our exposure to light and darkness occurred in a very predictable way. But the light has become very cheap. We all have smartphones and their screens are very bright. We are all exposed to light at the wrong times of the day. It is becoming increasingly important to understand how these different types of light information are relayed to the brain. "

Tiffany Schmidt, Principal Investigator, Northwestern University

When light enters the eye, it strikes special cells located at the back of the retina, called intrinsically photosensitive retinal ganglion cells (ipRGC). A signal is then transduced to the nerve cells that transmit the message to the brain.

Previously, scientists thought that these signals propagated in the region of the SCN brain. The SCN, also called the circadian brain stimulator, can regulate the circadian rhythm.

"The bright information arrives in the SCN, and that is what syncs all the clocks of the body with the light / dark cycle. This unique stimulator ensures that everything is synchronized, "said Schmidt.

The new study shows that the SCN is not the only region to receive bright messages. To prove it, Schmidt and his team used genetically modified mouse models. The genes of these mice have been modified so that the ipRGC are projected only on the NSC and not on any other region of their brain.

The team writes that mice are normally nocturnal and when there is light, they tend to fall asleep. The researchers found that these genetically modified mice whose SCN regions of the brain received the light alone were awake when exposed to light.

When these mice were exposed to short light pulses (similar to light pulses for humans using smartphones in the middle of the night), they remained awake. This means that the short light pulses did not affect the waking of the mice.

The short-term exposure to light also did not alter the body temperatures of the mice and their sleep-wake cycles and their circadian rhythms remained intact with short light pulses.

The researchers explain that this study shows that a night of activity in a smart phone in the dark can affect sleep that night and make the person drowsy the next day. Despite this, there is no long-term effect on a person's sleep habits.

If both of these effects – acute and long-term exposure to light – went through the same path, any exposure to minor light could completely change the circadian rhythms of our body. "

Tiffany Schmidt, Principal Investigator, Northwestern University

Thus, researchers were confident that there were multiple pathways through which light information reached different parts of the brain and that these areas were not yet clearly mapped, Schmidt said.

She added that a small amount of light exposure during the night could help increase alertness. This could be useful for shift workers such as doctors, emergency staff, shift workers and nurses. These exposures to light may help maintain alertness but not alter or interfere with the circadian rhythm in the long term, she explained.

However, "The light at the wrong time of the day is now recognized as a carcinogen. We want people to feel alert when they are exposed to light without incurring the health risks badociated with off-beat circadian rhythms, such as diabetes, depression and even cancer, "warns Schmidt.

The study was funded by the National Institutes of Health and others. It was a collaborative work between Schmidt and Fred Turek, neurobiology professor Charles and Emma Morrison in Weinberg, and Samer Hattar, section chief at the National Institute of Mental Health.