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22 September 2014

How it is possible to live fairly normally with half your brain missing

Chinese researchers have recently reported a case of a woman found to have no cerebellum, a part of the brain that usually contains half of its neurons.

By Michael Brooks

What happens when the formation of the brain goes catastrophically wrong? In many cases, it seems, surprisingly little.

Chinese researchers have recently reported a case of a woman found to have no cerebellum, a part of the brain that usually contains half of its neurons. In a normal brain, the cerebellum co-ordinates many motor functions, balance and speech. In its absence, however, the brain can make do.

Now not only would discovering how that happens be fascinating, but it might also help us to understand the best way to help stroke victims or those with other forms of brain damage. This Chinese woman, whose story was first reported by New Scientist magazine, is about to find she’s very popular with neuroscientists.

The researchers describe their patient, who is 24 and married with a child, as having “mild mental impairment and medium motor deficits”. She has always struggled with her balance. Her speech was slow to develop and remains slightly slurred. Yet no one ever suspected that an entire part of her brain might be missing. It was only when she turned up at a hospital after a month of nausea and dizzy spells that a CAT scan showed the absence of a cerebellum.

She is the ninth person on record to have a near-normal life without that part of the brain. And it’s possible to live with even bigger brain abnormalities. In 1980 the journal Science reported that a student at Sheffield University with a slightly larger-than-normal head was found to have “virtually no brain”. That’s not quite a fair representation: scans showed that the outer 4.5 centimetres of the student’s brain had been crushed to a thickness of a few millimetres because the central part of the brain had been swelled by a flood of cerebrospinal fluid.

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The man is still out there somewhere, presumably. He was in every respect a normal, functioning human being and gained a first-class degree in mathematics. You might even say that he was better than normal: he had an IQ of 126, where 100 is the average. Not that the brain-squeeze was responsible for that. A similar developmental abnormality was reported in the Lancet in 2007 in a 44-year-old French civil servant. His IQ was measured at 75.

There are many cases in which brain malformations have terrible results. The new report from China, to be published in the journal Brain, notes that an absent cerebellum is associated with a high mortality rate. The brain can’t always compensate – but that it occasionally does is good news.

The Chinese patient will undergo various tests to see which part of her brain is compensating for the absent cerebellum. At the moment, the smart money is on the cortex having taken on a new role. The brain is capable of extraordinary plasticity.

As a result, doctors’ assessments of the likely consequences of brain damage might need revision. It might also improve our chances of successfully building a useful artificial brain.

The European Commission-funded Human Brain Project aims to simulate the brain, using electronic circuits in order to investigate what goes wrong in conditions such as Alzheimer’s and Parkinson’s diseases. When you consider that the typical human brain has roughly 14 billion neurons, each of which has 7,000 or so connections to other neurons, that seems a daunting task. However, brains that function though missing a clutch of neurons suggest that we might not need an exact reproduction before useful things arise.
Watch this space.