A few extreme cases show that people can be missing large chunks of their brains with no significant ill-effect – why? Tom Stafford explains what it tells us about the true nature of our grey matter.

How much of our brain do we actually need? A number of stories have appeared in the news in recent months about people with chunks of their brains missing or damaged. These cases tell a story about the mind that goes deeper than their initial shock factor. It isn’t just that we don’t understand how the brain works, but that we may be thinking about it in the entirely wrong way.

Earlier this year, a case was reported of a woman who is missing her cerebellum, a distinct structure found at the back of the brain. By some estimates the human cerebellum contains half the brain cells you have. This isn’t just brain damage – the whole structure is absent. Yet this woman lives a normal life; she graduated from school, got married and had a kid following an uneventful pregnancy and birth. A pretty standard biography for a 24-year-old.

The woman wasn’t completely unaffected – she had suffered from uncertain, clumsy, movements her whole life. But the surprise is how she moves at all, missing a part of the brain that is so fundamental it evolved with the first vertebrates. The sharks that swam when dinosaurs walked the Earth had cerebellums.