A new study carried out in flies has found that swallowing may be a key control circuit that tells their brains to release serotonin. The team from the University of Bonn in Germany and the University of Cambridge in the UK conducted a study on fruit fly larvae that have the advantage of having fewer neurons: about 10,000 to 15,000 compared to the 100 billion in the human brain. The study published in the journal Current Biology found that special sensors in the larvae’s oesophagus triggered a release of serotonin, the hormone associated with pleasure when they swallowed food. This mechanism e…