Experiments within living brains have revealed key neurons that control a stage of deep slumber called rapid-eye movement (REM).

In mouse studies, scientists led by Antoine Adamantidis of McGill University in Montreal, Canada, engineered a group of neurons so that they could be controlled by external pulses of light in the brain region linked to REM sleep. The neurons make a peptide called melanin-concentrating hormone (MCH).

Activating these cells with light increased the likelihood that mice entered REM sleep and extended its duration by 47%. Silencing the neurons reduced the quality of REM sleep (as measured by brain waves called theta oscillations) but did not shorten it.

The neurons may increase the stability of REM sleep by suppressing neighbouring neurons linked to arousal and wakefulness, the authors say.

Nature Neurosci. http://doi.org/nwv (2013)