For large swathes of the brain, the neurons we’re born with are the ones we’re stuck with. But a few small areas, such as the hippocampus, create new neurons throughout our lives, through a process known as neurogenesis. This production line may be important for learning and memory. But it has particularly piqued the interest of scientists because of the seductive but controversial idea that it could protect against depression, anxiety and other mood disorders.

Now, by studying mice, Jason Snyder from the National Institute of Mental Health has found some of the strongest evidence yet for a connection between neurogenesis and depression (or, at least, mouse behaviours that resemble depression). He found that the new neurons help