The man with two brains

Joe can work both half-brains simultaneously

A man whose brain was separated down the middle to treat epilepsy is helping scientists understand how the organ works.

The story of Joe, who had the dramatic operation in an attempt to ease severe epilepsy, is told in the BBC documentary "Brain Story".

The surgery involved cutting the main connections between the left and right hemispheres of his brain.

The end result does not appear to have been particularly detrimental - even though Joe is effectively functioning with two separate brains.

This is well illustrated by his "party trick" - being able to visualise and draw two different shapes, one with each hand, at exactly the same time.

The advantage of separating the two halves is that scientists can then ask each side to carry out different tasks - with no assistance from the other side.

Joe's brain has been separated into two halves

The results on Joe are helping them understand the differences between the two halves.

The left hemisphere is always considered to be the part of the brain which develops some particularly human skills, such as language.

And indeed, Joe's left brain performed well at these, while his right did not.

However, when puzzles which involved looking and absorbing information from shapes - even those simple enough to be solved by mice - were carried out, the right brain was the winner.

Professor Michael Gazzaniga, from Dartmouth College, New Hampshire, US, has been working with "split brain" patients for 30 years, and has his own theories about how the modern human brain has developed.

Dumber half

He said: "Take a split brain patient and measure their preoperative IQ and problem solving.

Professor Gazzaniga has spent years studying the brain

"Then you disconnect their hemispheres, and go back and measure the left hemisphere's IQ and problem solving, and it hasn't changed a whit.

"The right hemisphere is, on the other hand, kinda dumb."

The visual test produced the opposite result: "The left hemisphere just fell apart - just couldn't do the test.

"Maybe the left hemisphere begins to mutate in order to develop language, and as the language requires more cortex and more cortex, perceptual processes that used to be in the left get squeezed out."

"Brain Story" is broadcast on Tuesday at 2200 GMT/ 2100 BST on BBC2.