Differences in brain activity between the left and right hemispheres may explain why people often sleep poorly in new environments.

Yuka Sasaki at Brown University in Providence, Rhode Island, and her colleagues imaged the brains of people sleeping in an unfamiliar setting, and measured slow-wave activity, a signal associated with non-rapid eye movement (NREM) sleep. During the first night, they found weaker activity in the left hemisphere than in the right — an effect that disappeared on subsequent nights. The researchers also found that on the first night, sounds played to the right ear (which are processed by the left hemisphere) elicited greater brain activation and were more likely to wake the person up than sounds played to the left ear.

The authors speculate that lighter sleep in one hemisphere could have evolved out of a need for vigilance in new environments.

Curr. Biol. http://dx.doi.org/10.1016/j.cub.2016.02.063 (2016)