It's been a long time since I did sums by counting on my fingers. What changed so I could do them in my head?
Neuroscientists have worked out that a bit of the brain called the hippocampus changes as you do more sums. As you get older you start to memorise simple sums and the hippocampus, which plays a big role in memory, changes to enable you to do maths in your head.
The study involved scanning the brains of children, teenagers and adults to see how they changed.