US, Brown University – A study published on Wednesday revealed that whenever people sleeps in an unfamiliar place, one hemisphere of the brain takes the effort to stay awake in guard for potential danger. This could be traced back to an instinctive feature of human ancestors, as a preventive measure taken by the brain when sleeping in an unknown location.
The same brain function is known to be present in birds and marine animals, as sparrows, for example, are able to sleep with one eye open.
Researchers from Brown University’s School of Cognition and Brain Science and School of Psychology monitored slow-wave brain activity on 35 students at the university. It was noted by the research team that on the first night of sleep in the lab, slow-wave activity was much higher in the right hemisphere when compared to the other hemisphere in subsequent analyses.
The researchers proceeded to monitor the brain activity of the participants while they were subjected to a hearing test. A continuous tone was played as the students slept, then a single beep of a different tone was emitted. The brains responded with activity only on their left side. When a much louder tone was played, the research team realized that the participants who had the loud tone played on their right ear woke up faster. This happened because the right side of the body is the one connected to the left side of the brain.
The “first-night effect”
On the first night, 80 percent of the neurological responses were linked to the sound experiment; the following day of tests, the percentage dropped down to 50.
The results showed that the brain’s right hemisphere seemed to be immersed in slow-wave sleep, while the left hemisphere was in a state of “enhanced vigilance,” as it was more responsive to external sounds; the left hemisphere of the brain being the one responsible for logical thinking, cognitive behavior and reasoning.
This is not the first experiment of its kind, as Niels Rattenborg led a similar study in 1999 using ducks that revealed exactly how an organism would benefit from sleeping with half of the brain still awake. Rattenborg set ducks on lines and examined them while they slept. He found out that the ducks that happened to be surrounded by other ducks set their whole brains to sleep, but the ones located at the end of the line remained with one hemisphere of the brain awake, while also directing their eyes away from the other ducks.
The half-brain sleep mechanism seemed to help animals (and now, humans) to be on the watch for predators as they sleep through the night. Researcher of the “first-night effect” study, Yuka Sasaki, argued that brain activity on sleep is completely unconscious, so it is not yet possible to organically manipulate our bodies to have a full and deep sleep on the first night in an unfamiliar location.
Source: Cell