John Lorber was a pediatrician, not a neurosurgeon.
He made some outlandish claims on British television in the 1980s, and really misrepresented his intriguing findings.
The patients he profiled were adolescents of apparent normal social functioning, although some doctors reviewing his claims suspect that he exaggerated their cognitive and social functioning for dramatic effect. He provocatively named his program, "Is Your Brain Really Necessary?"
The patients he profiled had late onset hydrochephalus, or water on the brain. This occurs when the cerebrospinal fluid which circulates becomes dammed up in the brain and causes pressure and compaction of the brain against the skull. It usually leads to severe mental retardation and death (My father was a pediatrician, and I remember such a diagnosis was always grave and devastating to the patient's family).
Lorber's patients profiled in the TV program had brain hemispheres that were compressed such that some were only one centimeter in width. Thus, the volume of their brains had been diminished, but the mass was still there. Thus, it is misleading to say they only had 5-10% of their brains left.
Anway, clearly the brain is necessary, and clearly these patients were not "normal."
Here's a link discussing the Lorber cases in a brief section beginning at Page 14 of this Word document.
Exploding the 10 Percent Myth
Happy reading.
AS
[Edited to comment re: link. Sorry, apparently the link address I copied into this doesn't get you there. I can't seem to get at the address directly, because it asks me if I want to open the document with Microsoft Word and I say yes. Claus, I hate to give you more search terms, but I can tell you exactly how I got the link.
Google and enter these terms: "John Lorber" neurosurgeon Sheffield without brain man
Choose the Matching Result Number 3. It should ask if you want to open with Microsoft Word. It's a 23 page document. Not bad reading, and it's a pretty trustworthy source.]