In 2019, a case report in the journal Cell described a young woman who had grown up without a cerebellum. The cerebellum contains more than half of all the neurons in the brain. She had experienced some motor difficulties and speech problems growing up, but was living a functional adult life. She was 24 years old before a brain scan revealed that an entire brain structure was simply absent.
The brain, it turns out, is considerably more adaptable than its reputation for fragility suggests.
What different parts normally do
The cerebellum coordinates movement, balance, and timing. The left hemisphere houses language production (Broca’s area) and language comprehension (Wernicke’s area) in most right-handed people. The prefrontal cortex handles executive function — planning, decision-making, impulse control. The visual cortex at the back of the brain processes sight. The hippocampus consolidates memories.
These localisations are real. But they are not as fixed or as final as the textbook diagrams imply.
Neuroplasticity and compensation
The brain’s ability to reorganise — particularly during development — is substantial. When damage occurs early in life, neighbouring regions can take over functions that the damaged area would normally have performed. Children who undergo hemispherectomy (removal of one entire hemisphere, performed for severe drug-resistant epilepsy) often recover language and motor function to a degree that would be unthinkable if the same surgery were performed in an adult.
The woman missing her cerebellum had presumably been compensating since birth, with other motor regions recruiting to handle the functions the cerebellum would have performed. The compensation was imperfect — her coordination and speech were affected — but functional.
Adults are different
Plasticity diminishes with age. An adult who suffers a stroke affecting Broca’s area will typically experience significant and sometimes permanent language impairment. The capacity to reorganise hasn’t disappeared entirely — rehabilitation after stroke genuinely works, and imaging shows functional reorganisation occurring during recovery — but it is slower, more limited, and less complete.
What this means for understanding the brain
The cases of people surviving with significant missing or damaged brain tissue tell us something important: the brain is organised around functions, not locations. Locations are where functions usually live, not where they must live. Given time, alternative biological architectures can sometimes achieve the same functional outcome, even if the neural implementation is different.
This informs how aggressively a surgeon can resect brain tissue without producing permanent deficits, which varies by the region involved and the age of the patient. And it is a reminder that the brain’s labels in an anatomy textbook are useful maps, not inviolable territories.