What's the old brain? It's the part of the brain that we share with the earliest brains in existence - and it's also the part that controls all the things that keep you alive without you even thinking about it, like breathing and your heart rate. In today's episode, we talk about the various parts of the old brain and how they're linked together in health and disease, as well as tackling the idea that our brains' shape can predict our intelligence and that we only use 10% of our brain.