Neuroscientists say they've discovered how the drug ketamine works against depression. They've used experiments in mice to pinpoint a specific part of the brain where the drug seems to be most active.

So, following these discoveries - why isn't the drug more widely used?Guest: Dr Jonathan Webb, ABC Science Editor

Brainteaser (answer in the audio):Alice and Bella run a 100-metre race and Bella wins by 10 metres.They run it again, but this time Bella starts 10 metres behind the starting line.If they go at exactly the same speeds in the second race, who wins? For more of the latest science news, look for the science section on the ABC News website and sign up to a weekly email newsletter.