Why does payday feel good? You can’t eat money, and it can’t have your babies — so how did that 'ker-ching!' feeling become so sweet?

Working with rats, neuroscientists have gained an insight into how the brain comes to take pleasure in abstract rewards. Animals, they suggest, have a reward system that focuses on specific outcomes — what an action would achieve — which in turn plugs into a more general system that lets us know what feels good.