By MICHAEL HANLON

Last updated at 08:51 17 April 2008

What does it mean to be human, to be in control of one's own mind?

What is the nature of consciousness, the mysterious property of self-awareness that we all have and yet which no scientist understands?

Is there any such thing as free will, or are our minds at the mercy of some unknown force?

These are the fundamental questions that have perplexed philosophers and, increasingly, scientists for centuries.

Until recently they seemed utterly unfathomable; after all, how do you test for something like free will in the laboratory?

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But now science is coming up with some fascinating - and deeply uncomfortable - answers.

This week, for instance, Professor John-Dylan Haynes and colleagues at the Max Planck Institute in Germany report the findings of an extraordinary experiment which seems to show that "free will" - the most cherished tenet of humanity, which decrees that Man has total control of his own actions - may, in fact, be little more than an illusion.

For in their experiment, the scientists found that we may not be making conscious choices at all.

Rather, our subconscious minds may be dictating our actions, long before we realise.

It is a troubling suggestion. As Prof Haynes says: "The impression that we are freely able to choose between different possible courses of action is fundamental to our mental health."

If we are not in control after all, then that makes humans little more than automatons.

In his experiment, volunteers were asked to view a stream of letters on a computer screen and told, at some point, of their choosing, to press a button either with their left or right index finger - and remember the letter that was on the screen when they did so.

The volunteers were also connected to brain-scanning MRI machines which were able to monitor and analyse brain patterns.

These "mind-reading" scanners could recognise when the brain had decided on a course of action.

To the researchers' astonishment, it turned out that the volunteers' brains would reach a decision about pressing one of the buttons several seconds before the volunteers actually thought they had made up their minds.

The implications are hugely significant, because the experiment suggests that what we think of as a "conscious decision" may, in fact, be no such thing.

The traditional "folk science" picture of the mind has our "conscious self" as a little man sitting in our heads, pushing buttons and pulling levers, filing "thoughts", receiving messages from eyes and ears and making our muscles move.

What Prof Haynes's experiment seems to show is that we need a new picture; instead of that little man pushing and pulling levers, he is merely a passive observer, lazing back in his chair and watching it all happen.

It is as though what we are actually aware of is no more than a film show, and the decision-making is made purely unconsciously.

It is a disturbing picture, because it reinforces the view that we are mere machines, pieces of biological clockwork that have no more free will than a Swiss watch.

This sounds counter to common sense, but the more you think about it the more it is clear that much of what we do is done on "autopilot" and that free will is rarely necessary.

If you regularly drive to work, for instance, at the end of your commute tomorrow try to remember the details of your journey.

The chances are you will not be able recall more than the basics. When top tennis players are asked to think, consciously, about every stroke and every movement, their game falls to pieces.

Studies of elite sportsmen show that at the top of their game they are performing in a sort of semi-conscious fugue, purely on autopilot.

The "will", if there is any, comes during the training process, not during the match.

Of course, if we really do not have free will, this opens a can of worms about human morality.

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If the brain is a machine, whose decisions are entirely out of our conscious control, then can a criminal be held responsible for his actions?

This is a dangerous road to go down. As Prof Haynes admits: "It would lead to no one being held responsible for anything."

But this isn't the first time science has given a worrying insight into the workings of our brains.

Earlier this year, Nature magazine reported an extraordinary experiment in mind-reading technology.

No stage magic, smoke or mirrors here - just the clever use of brain-scanning machines and computers to pinpoint and identify actual thoughts as they arise in the brain.

The scientists, led by Dr Jack Gallant of Berkeley University in California, again used MRI scanners to monitor brain activity when volunteers were shown various black and white photographs of everyday scenes - a house and garden, various countryside views and so on.

The scanner and the computer it was attached to first had to "learn" how the brain reacted to thousands of images - what electrical patterns arose when the volunteer was looking at a picture of, say, a house or a car.

The volunteer was then shown photographs and the "mind-reading system" had to work out, from the patterns of electrical activity detected in the brain, what the subject was looking at.

Astonishingly, nine times out of ten the machine was able to work out what the person was looking at.

As the authors freely admit, the way is now open to a general mind-reading machine, "perhaps even to access the visual content of purely mental phenomena, such as dreams and imagery".

If we can read minds, and even dreams, and prove that free will is a nonsense, then what does that say about the mystery of our minds?

In fact, the human brain, for all this, remains by far the most mysterious object known to science.

by the most mysterious object known to science.

It is still completely unknown how 3lb of wet jelly, plus tiny electrical currents powered by the energy we release from our food, can give rise to consciousness. But it does.

Few modern people believe that the brain is pervaded by some sort of mysterious "soul"; but how the neurones and synapses of the mind can generate subjective experiences of colour, smell, hate, fear and love is an utter mystery.

In fact, many scientists believe it is the greatest mystery of all.

But unless we want to believe in "souls" or "auras", we must believe that the brain is a machine - a very complicated machine, but a machine nonetheless.

And that means its workings must, in principle, be deducible, that we can predict its every move, as this freewill experiment seems to show.

Does that mean we will one day be able to calculate what powers love, creates artistic masterpieces, sows awe, and experiences both great sorrow and utter joy?

Maybe one day science will have an explanation for all this, but one suspects that even after the questions of the atoms and quarks, the planets and galaxies are finally answered, the deep puzzle of what exactly is going on in our heads will remain forever unsolved.

And perhaps that's the way it should be.