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"Your brain operates on a need-to-know basis and most of the time you don't need to know.

" This is how Professor Chris Frith [¹û¶³Ó°Ôº Institute of Neurology] sums up the relationship between our brains and our minds.

And he puts forward a mind-boggling prospect: the majority of the work that your brain does goes on unconsciously. …

Professor Frith, along with other leading brain experts, this week was examining the topic of consciousness and the mental world in which we live, at this year's British Association for the Advancement of Science Festival in York. Their starting point was that our brains are constantly soaking up and processing information from the world around us, monitoring, checking and assessing. But most of the information from our 100 trillion or so brain cells never reaches us. Instead the brain takes this raw data to create a model of the world and this is the mental world in which each of us lives. …

Professor Frith, who wrote a book on the subject called Making Up the Mind: How the Brain Creates our Mental World (Blackwell, £14.99), says that if we start to think about how we do things - for example if you start thinking about how you physically move your limbs, or how you actually understand the meaning of these letters on the page - you start to get a bit confused and your brain doesn't work as well. …

So how have scientists worked out that most of our brain activity is unconscious, and what is actually going on inside our heads?

To answer the first question, Professor Frith says the fact that we can do many skills at once - for example, driving a car, while thinking about something completely different, such as what to buy for dinner - has suggested that there are many conscious levels in our brain. …

"In one of my experiments we showed a group of people a pattern on a computer screen, while scanning their brains. We then flashed up an image of a scared-looking face, just for an instant. We asked them if they had seen a face, and, because it was only on the screen for 100th of a second, they said no. However, our results showed that their brain had seen the face. The amygdala, the area associated with fear, had suddenly become active," says Professor Frith. …

So does our brain physically contain conscious bits and unconscious bits? Roughly speaking, yes, says Professor Frith. "The back of the brain deals with perception and the front of the brain deals with action," he says. …

Kate Wighton, 'The Times'