A new BBC series which begins tomorrow aims to unravel the mysteries of the human brain. As STEPHEN LEWIS discovered...

It's the most important organ in the body - and the least understood. The brain holds our thoughts, hopes, dreams, memories and personality. It's what makes us who we are. But as a new BBC series which begins tomorrow reveals, scientists are still struggling to unlock the many mysteries of the brain - and to find out more about what really makes us tick.

Susan Greenfield, Professor of Pharmacology at Oxford University and probably Britain's leading female neuroscientist, has no truck with those who speculate about a human soul which exists above and beyond the physical body.

All aspects of human experience, she believes, will eventually be explained in terms of the physical processes of the brain.

"I'm convinced there isn't a single aspect of our lives that doesn't reside in the sludgy mass of our brain cells," she says, robustly.

That, though, isn't in any way to demean what it is to be a human being. Because the human brain is an amazing thing.

Scientists estimate that there are between one hundred and two hundred billion neurons, or nerve-cells, in the human brain. That's 200,000,000,000. It's the connections between these - the 'pathways' in the brain - that carry our thoughts, memories and dreams. And the number of these possible different connections is believed to be larger than the total number of atomic particles that make up the known universe.

That's pretty big. Plenty of room there for the elusive self to hide, without needing to postulate the existence of a God to explain our unique sense of individuality. The human brain, in fact, is by far the most complex computer known to man. At the current rate of computer chip development, experts believe, it will take about 35 years to develop an artificial computer with anything like the same computing power.

You really are amazing. But before you get too carried away, it's worth remembering this, too. Eighty-five per cent of your brain is ordinary, common-or-garden water.

Andy Young, Professor of Neuropsychology at the University of York, concedes there is still far more to learn about the human brain than we have been able to understand so far.

"It is one of the great scientific mysteries," he said. "There is far more that we don't know about the brain than that we do know."

In theory, he says, it should be possible one day to understand at least the principles behind the way the brain works. One recent area of research is measuring the amount of blood needed by different parts of the brain when particular tasks are being performed.

When a part of the brain is working hard, Prof Young says, it needs more oxygen, and so more blood. That makes it possible to begin to develop a 'map' of the brain, showing what each area is 'for' - although not how it works.

But the real key to understanding what we are, Prof Young says, lies not only in unravelling the mysteries of the brain itself: but also the way it interacts with the outside world. That it does so is beyond doubt. Scientists, for example, have been able to show that a certain area of the human brain is responsible for processing the information that enables us to recognise individual human faces. It's a hugely complex task involving recognition of immensely subtle differences, but one that is very important to us as people. It is also a process that very definitely involves our brain interacting with information about the outside world.

The benefits of an improved understanding of how the brain works, Prof Young says, are 'potentially immense' - with massive implications for the treatment of brain injury and degenerative conditions such as Alzheimer's Disease. And recent developments are opening up possibilities that were only dreamed of 20 years ago.

The BBC's new series aims to look at some of these new developments - and unravel some of the mysteries of the brain at the same time. It promises to be literally mind-boggling viewing. In one programme, presenter Prof Greenfield meets patient Sarah Kitchen while she is undergoing surgery at the hands of neurosurgeon Henry Marsh to remove a brain tumour. Because of the size of the tumour, there's a danger the surgery could damage the area of Sarah's brain responsible for speech. So she's kept awake for this part of the operation - and asked to keep talking. With half her skull removed and the operation still going on, she swaps ricotta recipes with the professor.

In another programme, the professor meets a woman with a form of epilepsy that causes her to see colours very vividly and to experience intense religious hallucinations - two distinct characteristics of Vincent Van Gogh, who was also a sufferer.

The professor sets out to investigate whether spiritual feelings can be 'induced' artificially by stimulating a particular part of the brain - in the same way neurosurgeon Mr Marsh could cause his patient Sarah to talk or be silent merely by prodding a part of her brain tissue.

u Brain Story begins on BBC2 tomorrow at 9pm. The book to accompany the series will be published by BBC Worldwide on July 27 priced £17.99.

PICTURE: a brain scan taken from the title sequence of BBC2's Brain Story.