Scientists left stunned after discovering man was living normal life with 90% of his brain missing

In a case that continues to challenge scientific understanding of the brain, researchers are examining how a man with only about 10 percent of his brain tissue manages to live a regular life.

Following an MRI, the scans shown that most of the mans skull was filled with fluid, instead of brain tissue.

While it was initially thought that brain tissue had eroded, scientists now believe that it was compressed by the fluid.

The brain tissue was compressed into a thin outer layer along the edges of his skull, leaving 90 percent of the skill filled with fluid, instead of brain matter.

Despite the extreme reduction in brain volume, the Frenchman leads a fairly healthy life and is employed and married with two children.

The French man went in initially complaining of leg pain (Monty Rakusen/Getty Images)

He shows only mild intellectual impairment. His IQ was measured at 75, which is below average but not low enough to qualify as intellectually disabled.

The condition is the result of hydrocephalus, a disorder involving the build up of fluid in the brain.

He had been treated for it as a child, in which he had a shunt inserted to drain the fluid.

The shunt was removed when he was 14.

Over time, the fluid slowly accumulated again and seemingly compressed his brain tissue.

The scans left doctors baffled (The Lancet)

Neurologists in France are intrigued by how well the man functions given how little brain tissue remains in tact.

Cognitive psychologist Axel Cleeremans from Université Libre de Bruxelles uses this case to advocate his 'radical plasticity thesis'.

It was previously believed that consciousness stems from a single part of the brain. However, according to Cleeremans: "Any theory of consciousness has to be able to explain why a person like that, who's missing 90 percent of his neurons, still exhibits normal behaviour."

Cleeremans believes that people aren't born with consciousness in a single part of the brain. Instead, he believes that its location can be flexible, and learnt by different parts of the brain, which would explain why this man has lost 90 percent of his brain still exhibits normal behaviours.