In 2007, a 44-year-old happily married man with a white-collar job and two children visited a hospital in Marseille, France complaining of mild weakness in his left leg. Some time later, he concluded his hospital episode with his leg weakness cured, but with another, intriguing diagnosis in tow: he was missing most of his brain.

A disconcerting notion to most, the condition didn't seem to trouble the man much at all. Sure, his IQ tested a tad below average, but his medical history and neurological development were otherwise normal. So how did he develop his strange, yet innocuous infirmity?

The doctors soon learned that when he was just six months old, the man had a condition called hydrocephalus, where an excess amount of cerebrospinal fluid accumulated in the ventricles of his brain. Luckily, it was caught early, and doctors inserted a shunt -- a valve of sorts -- to ensure that the fluid drained properly. Fourteen years later, the shunt was removed.

Perhaps it should have been left in, because over the next thirty years, the fluid gradually built up in the ventricles, ever so slowly condensing or consuming the actual brain matter until it only remained at the outer recesses of the skull.

How the man was able to function normally remains a mystery, but then again, so do many aspects of the brain's operation. The best explanation scientists gave is that the brain is plastic and highly adaptable.

Discover Blogs' Neuroskeptic offered another theory:

While the enormous “holes” in these brains seem dramatic, the bulk of the grey matter of the cerebral cortex, around the outside of the brain, appears to be intact and in the correct place – this is visible as the dark grey ‘shell’ beneath the skull. What appears to be missing is the white matter, the nerve tracts that connect the various parts of the cerebral cortex with each other, and with the other areas of the brain.

According to Neuroskeptic, instances like these call into question how much white matter is truly needed for the brain to function properly. Could it be that a good chunk of the 1,400-gram human brain is superfluous?

Perhaps by closely studying more of these cases of "missing brain," scientists can find out.

(Images: Feuillet et. al./The Lancet, Frontiers in Neuroscience)

