Most people will have experienced the so-called first-night effect at some point in their life. When sleeping in an unfamiliar setting for the first time, it is likely to take longer to drop off, and the sleep we finally do get will be broken and unsatisfying. For the first time, scientists have discovered why this might be.

Although the first-night effect (FNE) has been part of the human experience since humans first slept in a new cave, the science behind it has remained a mystery.

The FNE is so familiar and consistent that sleep researchers routinely discard the first night of data, as they know it will be unusual and, therefore, unusable.

Researchers from Brown University in Rhode Island, led by Yuka Sasaki, set out to investigate the odd phenomenon in more depth.

The team wanted to know why the FNE occurs, and whether there is any benefit to it.

Using advanced neuroimaging techniques to take snapshots of the sleeping brain, the team built up a detailed picture of the sleep activity during the first night in a new location.

Measurements included magnetoencephalography, structural MRI (magnetic resonance imaging), and polysomnography (measuring blood oxygen levels, breathing and heart rate, eye and leg movements).

Slow wave sleep, rather than REM (rapid eye movement) sleep, was the main parameter that the team focused on because it acts as a direct measurement of the depth of an individual's sleep.
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