For many people, whether it’s a business trip, a vacation or just a visit to a friend, sleeping in a new place could mean a restless night. Called the “first night effect” in a new study from Brown University, researchers have shown that one hemisphere of the brain more alert than the other, as if on guard against trouble.
The study is published in the journal Current Biology explains how the brain works during a night in a new sleeping location. While it’s a minor bother when traveling, in lab studies where participants have to spend a night in the lab, it could mean that an extra night must be planned to allow people to adjust to the new environment, so that study results are more accurate.
Study corresponding author Yuka Sasaki, a research associate professor of cognitive linguistic and psychological sciences at Brown and lead author Masako Tamaki wanted to understand more about how the brain manages to stay somewhat alert during sleep. During the course of three overnights with a total of 35 study volunteers they used several methods to precisely measure brain activity during two nights of sleep, a week apart. Their results were consistent on the first night of sleeping in the lab environment. They found that a specific network in the left hemisphere of the brain stayed more active than the right side. This was particularly noticeable during the period of deep sleep known as “slow wave” sleep. They found this by playing an annoying beeping noise into right ear of sleepers to stimulate the left hemisphere and into the left ear to activate the right side. There was a much greater chance that the volunteer would wake up when the sound was played in the right ear, because the left hemisphere was not completely at rest, whereas the right hemisphere was much more dormant.
The team tested their theory in other phases of sleep as well as in other networks in the brain. Again the results stayed consistent, showing up only in the left hemisphere in the default mode network. The differences were not shown during the second night of sleep either, pinpointing that the brain’s state of alertness was unique to this one area and only on the first night of sleeping in a new place. The authors of the study wrote, “To our best knowledge, regional asymmetric slow-wave activity associated with the first-night effect has never been reported in humans. The present study has demonstrated that when we are in a novel environment, inter-hemispheric asymmetry occurs in regional slow-wave activity, vigilance and responsiveness, as a night watch to protect ourselves”
The researchers used electroencephalography, magnetoencephelography, and magnetic resonance imaging to make unusually high-resolution and sensitive measurements with wide brain coverage. Volunteers in the study were screened for general health and reported to anxiety or stress over sleeping in the lab or wearing the equipment and submitting to the scans. The authors acknowledged that the study only measured the brain’s activity during the fist slow wave sleep phase, so it’s not known if the brain alternates between hemispheres as the night wears on. The video below explains more about how the brain keeps watch, check it out.
Sources: Brown University
, Current Biology