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Brain Story - 2/6

In The Heat Of The Moment

Professor Greenfield explores the complicated origins of human emotions in this programme. She asks why emotions seem so different from thoughts. Human beings don't just 'think' emotions; they feel and experience them in a way which is physically manifest in facial expressions such as happiness, sadness and fear that appear to be common to all cultures and throughout human history. Susan looks at some of the most intense emotions, beginning with disgust, and meets Professor Paul Rozin, who spends much of his time attempting to revolt people.

She learns that this particular emotion is directly linked to quite basic sensations in the mouth and the stomach. But disgust can also be learnt; an adult will not want to taste a drink that has had an insect floating in it but a child may be quite happy to drink it once the creature has been removed. Susan explains how a specific part of the brain becomes activated when stimulated by images that the subject finds disgusting.

Vietnam veteran Dennis Sines has symptoms of post traumatic stress syndrome. He is jumpy and easily startled and has intrusive memories of his war experiences. 'I feel trapped in my life. I feel like I'm trapped in some kind of hell'something that's never going to go away.' An MRI scan indicates that the fear which Dennis experienced seems to have physically altered the structure of his brain.

And emotions are not just governed by physical areas of the brain; finely-tuned chemical balances may have a bearing on even that most complex of emotions ' love. But, for Susan, the answer to how ' and why ' humans experience emotion is far more complex than special areas of the brain or simple chemical changes. She believes it may be something far more subtle and mysterious. 'The indescribable sensations of different emotional states must actually emerge directly from the ever-changing patterns of nerve cells firing in the brain.' And while, at the moment, these neurone patterns cannot possibly be measured by scientists, Susan is convinced that 'in this new century, we'll be able to do just that'.