How much brain do we really need?

` Have you ever wondered that? A month ago, I was reading the Nature News item The man with a hole in his brain. (Free to non-paying members here.)
` I've always thought the myth that we only use ten percent of our brains was amusing. In fact, all parts of the human brain are active all the time; just enough to keep our neurons from dying, at least.
` However, at any given time, some parts of the brain are more active than others - for instance there are parts on the left side of the brain that contribute to different facets of language, and the entire occipital lobe (in the back of your head) is devoted to various aspects of visual processing.
` Astonishingly, there have been some normally-functioning people who have been said to have only ten percent of a brain! ...However, this is apparently an exaggeration. Nevertheless, the people I am referring to were hydrocephalics with large holes in their brains studied by such doctors as John Lorber, a former professor of pediatrics at Sheffield University.

` Hydrocephalus is a potentially serious condition where more cerebrospinal fluid flows into one's ventricles than out, resulting in a ballooning of pressure within the brain. The force is so enormous that it can squash the brain against the braincase and expand the as-yet unfused skull of an infant.
` Aside from causing seizures, convulsions and mental retardation, this condition can also be fatal if a shunt is not installed to allow the fluid to drain into other parts of the body. In several notable cases, however, such squashed brains have functioned almost normally!

` The Nature article talks of a case study made three years ago of man in Marseille, France. He had a wife, kids, an IQ of 75, and he worked as a civil servant. Three years ago, this man went to a hospital, informing staff of a weakened left leg.
` That was his only real complaint. Searching for neurological abnormalities, they found his brain wadded up into a thin layer to make room for the ventricles that took up most of the room in his braincase.
` "We were very surprised when we looked for the first time the CT scan," commented Neurologist Lionel Feuillet. "The brain was very, very much smaller than normal."

` I'll say. See for yourself!

` This man had probably been born with hydrocephalus. He had been given a shunt at six months of age, and had it fixed at 14 years when he had problems with his left leg. At 44 years old, this most recent complaint was the first time he had experienced neurological problems since then.
` How his brain had managed to develop normally currently escapes neurologists, but that doesn't mean it's impossible to explain:
` The pattern of the most prevalent difficulties in hydrocephalics (focusing and coordination) suggests that the areas immediately surrounding the ventricles are affected the most. If the brain retains a relatively normal structure during this stretching (despite damage), those would be the most-stretched areas.
` Importantly, the brain is able to re-route areas of functioning from damaged areas while it is developing; perhaps the pressure caused most of the brain deformation during development in the Marsielle man's case.

` It is hard to say just how his brain had developed; CT scanners were not around when he was having problems earlier in life. As for the his treatment outcome this time around, the fluid had been shunted once more, and his brain remained the same size.
` Who knows if we'll ever know. Perhaps he'll be kind enough to donate his brain to science when he's done using it?