THE bright light at the end of the tunnel which some people close to death describe may result from a flood of serotonin in the brain.

Near-death experiences (NDEs) are reported by around 1 in 5 critically ill people, and their cause is a mystery. Alexander Wutzler’s team at the Charité University of Medicine in Berlin, Germany, wondered if serotonin – a neurotransmitter involved in mood regulation and processing vision and sound – plays a role.

They gave six rats an overdose of anaesthetic and found that serotonin levels in their brains had tripled by the time they died (Neuroscience Letters, DOI: 10.1016/j.neulet.2011.04.051).

Wutzler expects to see a similar increase in dying human brains. He says serotonin could be behind NDEs, but Jakob Hohwy at Monash University in Melbourne is unsure. “One thing that you don’t want to say is that rats have NDEs,” he says.