That people often experience trouble sleeping in a different bed in unfamiliar surroundings is a phenomenon known to psychologists as the “first night” effect. This is because if a person stays in the same room the following night they tend to sleep more soundly. Yuka Sasaki and her colleagues at Brown University in Providence, Rhode Island, set out to investigate the origins of this effect.
Dr Sasaki knew the first-night effect probably has something to do with how humans evolved. The puzzle was what benefit would be gained from it when performance might be impaired the following day. She also knew from previous work conducted on birds and dolphins that these animals put half of their brains to sleep at a time so that they can rest while remaining vigilant enough to avoid predators. This led her to wonder if people might be doing the same thing and suffering from fatigue the next day as a result.
Dr Sasaki found that, as expected, the participants slept less well on their first night in the lab than they did on their second, taking more than twice as long to fall asleep and sleeping less overall. During deep sleep (as opposed to the lighter phases of sleep which are characterised by rapid eye movement), the participants’ brains behaved assymetrically, in a manner reminiscent of that seen in birds and dolphins. More specifically, on the first night only, the left hemispheres of their brains did not sleep nearly as deeply as their right hemispheres did.
Curious if the left hemispheres were indeed remaining awake to process information detected in the surrounding environment, Dr Sasaki re-ran the experiment while presenting the sleeping participants with a mix of regularly timed beeps of the same tone and beeps of a different tone made sporadically during the night. She worked out that, if the left hemisphere was staying alert to keep guard in a strange environment, then it would react to the random beeps by stirring people from sleep and would ignore the regularly timed ones. This is precisely what she found.
Read the complete article on The Economist here.