The first-night effect

Many of you might have faced this situation:

You visit a new place. Despite being exhausted, you  find it painfully difficult to fall asleep. And even if  you manage to get to sleep, you still wake up frequently in the night, or too early in the morning, feeling miserable.

Researchers have long known about this phenomenon in an experimental setting, terming it the “first-night effect”. Sleep study participants often sleep poorly during their first experimental session in a new environment and sleep quality usually improves dramatically on the second night.

So what happens in the brain when people sleep in a new place? In a study, published recently in Current Biology, scientists found poor sleep in an unfamiliar setting may be linked to an important function of the brain to protect the sleeper from potential danger. The amazing ways in which a human body works has been revealed!

Studies have indicated unilateral hemispheric sleep in some birds and marine mammals, where one hemisphere of the brain sleeps while the other is awake. This peculiarity has been connected to a survival strategy. Some birds show unilateral sleep in risky situations, such as when they sleep at the dangerous edge of a group rather than in the middle, so that the waking hemisphere can detect predators while the other half rests.

Something similar is happening in human beings too. When people don’t know whether a new place is safe or not, an inbuilt internal surveillance system kicks in. It doesn't allow you to fall asleep properly!

Scientists conducted a few experiments on people to test this and found the left hemisphere of participants' brains slept lighter than the right on the first night.

The experiments combined magnetoencephalography (MEG), that measures changes in the brain’s magnetic field; magnetic resonance imaging (MRI), that measures structural brain information; and polysomnography, that measures general sleep status.

A human brain is divided into two hemispheres, the left and right. Some parts of the left hemisphere are associated with language processing and some parts of the right with spatial information processing, or processing of the surrounding environment. 

Depth of sleep was also measured in different brain networks. Brain networks are composed of several different brain regions but they work together. One of these – the default-mode network – is linked to spontaneous mind wandering. So if someone’s mind wanders spontaneously, the default-mode network may be activated.

Scientists found it was the default-mode network that slept less when the left hemisphere slept lighter, suggesting the mind was wandering – or on some form of alert. They also found participants with stronger interhemispheric asymmetry in the default-mode network slept worse. The interhemispheric asymmetry in the sleeping brain was seen only on the first night when the environment was new. During the next session, everyone who participated in the experiment slept soundly.

Did the left hemisphere sleep lighter during the first session because it was monitoring the environment? If so, this hemisphere would also be able to react to subtle signals. The scientists tested this possibility in the next experiment. While participants slept, they were presented with two different beep sounds through earphones. One sound was of a high, unusual frequency, while the other was an ordinary frequency sound.

Most of the time, the participants would hear the normal sound, but once in a while, the researchers would present them with a rare sound. They  then measured how much each hemisphere responded to either sound.

They found the lighter-sleeping (left) hemisphere was more alert than the right when presented with an unusual sound. It actually responded strongly to unusual sounds but not as strongly to ordinary sounds. Again, these effects were only seen during the first sleep session and not the next.

This showed that like some animals, the interhemispheric brain asymmetry that happens on the first night in humans might act as a security guard to protect them from danger.

So don't worry when you are unable to sleep in a new place the next time. It is the evolutionary process at work and your brain is trying to protect you from a 'potential danger'. Smile. Your system is working alright. It is a positive sign!