Last week the world learned of a woman who has been living normally with no cerebellum. That's not the limit to the brain's plasticity either. This month a 24-year-old woman in China's Shandong Province walked into a hospital complaining of nausea and dizziness, and walked out having learned that she was missing a huge portion of her brain. A CAT scan showed that her entire cerebellum, a vital chunk of brain in charge of motor control, never developed. The void where it should have been was nothing but a swamp of cerebrospinal fluid. How could a person live a full life not knowing so much of her brain was gone? Her doctors believe that her cortex (a nearby area of the brain) took over most of the load as her incomplete brain developed, thanks to an amazing feature of the brain called neuroplasticity—the brain's ability to fundamentally rewire itself to cope with new demands. The brain can't cope with everything, and the more of it is lost, the less it can reassign functions to the remaining pieces. But neuroplasticity is nonetheless quite remarkable. The woman from China's is far from the only such bizarre and fascinating story. A short trip through the annals of modern medicine reveals even more surprising cases of missing brain structures. MISSING HALF OF THE CEREBRAL CORTEX There are a surprising number of known cases of people missing half of their cerebral cortex—the outermost chunk of brain tissue. A currently living and healthy 16-year-old German girl is one. She was born without the right hemisphere of her cortex, though this wasn't discovered until she was 3 years old. According to her doctors, who published a full case study on her 6 years ago, "despite lacking one hemisphere, the girl has normal psychological function and is perfectly capable of living a normal and fulfilling life. She is witty, charming, and intelligent." The physical ailments caused by her missing brain tissue were seizures (since treated) and a slight weakness on the left side of her body. But here's something amazing about the way her brain has coped: While most people missing half their cerebral cortex lose sight in one eye, her left eye processes visual information from both the right and left visual field. In other words, her doctors say that while she has no depth perception (which is dependent on two eyes seeing slightly different images), her vision is otherwise like that of someone with two eyes, encompassing the entire mental field of vision. MISSING HALF THE ENTIRE BRAIN In a more severe case, Michelle Mack, a 42-year-old Virginia native, is missing not only half of her cortex but most of the deeper, underlying brain structures on her left side as well. This neural abnormality is believed to be the cause of a prebirth seizure, but was not diagnosed until Mack was 27. Mack graduated high school and speaks and communicates with some level of normality—thanks to neuroplasticity. But her brain has not faultlessly rewired itself: Mack still has issues comprehending abstract concepts, is prone to emotional distress, and her lowered visual–spatial processing ability means that she also is easily lost in unfamiliar surroundings. Yet, living with her parents, she nevertheless manages a productive and fulfilling life. MISSING ALL BUT THE BRAIN STEM Trevor Waltrip, born in Louisiana on Christmas Eve in 2001, has defied the odds for 12 years. He lived without any brain at all save the brain stem. Trevor was born with a rare condition called hydranencephaly, which replaced his neural tissue with cerebrospinal fluid. His brain stem allowed him to breathe and maintain a heartbeat but little more. He was kept on a feeding tube up until last month, when he passed away peacefully. Source
