The cerebellum is a pretty important part of the brain—it plays a key role in walking, among other movements—so doctors in China were more than a little surprised when a 24-year-old patient who lives a relatively normal life turned out not to have one. A CT scan revealed nothing but cerebrospinal fluid where the "little brain," which contains around half the brain's neurons, was supposed to be, reports the New Scientist. The woman had sought medical help after experiencing a month of vomiting; she also noted she has always walked unsteadily. She has slightly slurred speech, and her mother told doctors she hadn't started walking until age 7 or speaking intelligibly until around age 6.
The woman, who is married with a daughter, has no history of neurological problems in her family, researchers write in the journal Brain. Only eight other people have ever been found to have the condition, known as cerebellar agenesis, but most other cases involved infants with severe mental impairment and were discovered upon autopsy, the researchers say. This case "shows that the young brain tends to be much more flexible or adaptable to abnormalities," a professor of neurosurgery at New York's North Shore University Hospital tells LiveScience, which notes that even a damaged cerebellum can cause severe motor challenges. "When a person is born with an abnormality ... the rest of the brain tries to reconnect and to compensate for that loss or absence." (But as adaptable as the brain is, it's a myth that we only use 10% of it.)