When Francis Crick began researching consciousness it was a relatively unploughed field. Now, he tells Kam Patel, it has become crowded with interlopers. It is a cool, sunny day in San Diego and from the window in Francis Crick's Californian office you can look out on the bright, steely blue waters of the Pacific Ocean. A magnificent view that you can imagine Crick musing over during his reflections on some problem or other.

More than 40 years have passed since Crick and James Watson unravelled the molecular structure of DNA, the piece of biological architecture that makes possible the transmission from parents to offspring of inherited characteristics. The achievement, one of the key breakthroughs of 20th century science, ushered in the age of molecular biology.

Crick, though, has little interest in discussing past glories. He will be 80 years old next month. The passage of time has done little to blunt his appetite for new intellectual challenges, which he tempers with a slightly mischievous sense of humour Q to considerable effect. He laughs a lot.

For the last 20 years Crick has been based at the Salk Institute in La Jolla working on the molecular and cellular aspects of nerve cells in the brain and the behaviour of organisms. In the past decade he and his collaborator, Christof Koch, have focused on developing a scientific explanation for the biggest puzzle of all: the origin and nature of consciousness, the problem of how our awareness of everything Q colours, pain, textures Q is formed. It is a question bedevilled by conflicting convictions and has attracted the attention of academics from fields as diverse as neuroscience, philosophy and computing.

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At Salk last month, shortly after an interdisciplinary conference on consciousness in Tucson, Arizona, Crick was keen to discuss the prospects for a field of research that has gained in scientific credibility by the mere fact of his participation. For when he and Koch began working on the problem of consciousness, few other scientists were interested in it. He admits he is in the fortunate position of being able to work on pretty much what he wants and says that until very recently, young scientists felt their reputations might be damaged if they worked on such a controversial question. This is changing but Crick still fears the progress made in creating serious scientific interest in consciousness is at risk. "There is now far too much general interest (as shown by this meeting in Arizona) and as far as we are concerned it is going to be a handicap. Unless we are careful, results will trickle out slowly and in a few years time there will be a reaction against consciousness, and it will become unfashionable again."

He believes the press has paid too much attention to the work. "Although it's an interesting problem, the results are very minimal. I don't think it's a good idea to encourage conferences like the one in Tucson." Jim Watson complained at the 40th celebration of the discovery of DNA that there were "DNA groupies" wandering around. Crick, laughing loudly, says he hears there are now "consciousness groupies" too. "It's getting a bit much."

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Not having been at the Tucson conference, Crick admits he could be accused of prejudice. But, having talked to a few people who did attend, his impression is that there was far too much "flakey stuff" there. What he would like to have seen is competent neuroscientists, psychologists and, yes, one or two philosophers, getting together quietly. After all, that is what happened in molecular biology Qthough Watson did get his picture in Vogue around the time the DNA structure came out. He laughs. "But you know, leaving aside that and one or two other things in the papers, we were able to work in peace and quiet until we managed to get something pretty substantial."

Above all he wants to do as much as he can to encourage good experimental and theoretical scientists into consciousness research. He says: "It's not that Christof and I think we are so clever that we can solve the problem ourselves. We want to be able to talk to people who have a serious interest in the problem so that we can remove errors from our thinking as far as possible. And it doesn't help to have all this other stuff. It's so distracting."

So what has Crick's research added to our understanding of the consciousness puzzle? Together with Koch, He has been tackling the problem through a detailed neurological, neuroanatomical and psychological study of how the visual system operates. The hope is that this will eventually enable them to explain how the patterns of communication between nerve cells in the brain translates into our visual awareness. The strong working hypothesis is that consciousness is caused by the activity of the nerve cells.

Much of their work has involved macaque monkeys. It is possible to inactivate a region of the cortex of a macaque monkey's brain by flooding it with a chemical called an inhibitory neurotransmitter. Since all the brain's nerve cells have receptors for this neurotransmitter, they all become "silent" or inactive. As the chemical is used up by the receptors the nerve cells become active again. This has already been done for one layer of the cortex and the effect on another layer monitored. While this is providing insights into the functioning of the monkey's cortex, the fact that whole areas rather than particular types of neurons are knocked out means it is of limited use. "And you cannot do it on people for obvious ethical reasons. It would be marvellous if you could. " There is no shortage of neuroscientific and psychological experiments that need to be done. Experimental work is crucial, Crick says, for developing a coherent theory. He is dismissive of the approaches some academics have brought to bear on the problem. He says he has already wasted far too much time on the controversial theories of the Oxford-based mathematician Roger Penrose, for example. Penrose argues that consciousness is generated by quantum events in tiny parts of the brain's nerve cells called microtubules rather than, as most scientists believe, by the large-scale behaviour of nerve cells. Arguments for and against a quantum explanation for consciousness were one of the flashpoints at the Tucson conference.

Koch attended the conference, bearing a letter that highlighted Crick's concerns about Penrose's ideas. The reply from Penrose was disappointing. "Penrose is convinced he is right. I can tell that from his letter. In fairness to Roger we must say that his sketch of a theory of quantum gravity is not necessarily implausible Q although not many people even agree with that. " In his reply to Crick, Penrose admits two problems worry him. For his theory to work, Penrose needs the quantum activity he believes is taking place in microtubules to be perfectly isolated from the cellular and extra-cellular environment surrounding them. But Crick argues that the microtubules would be affected by features of their environment. "He is worried about this and hopes there is a solution. The rest of us think it very unlikely," says Crick.

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Even more worrying to Penrose, according to Crick, is the large number of microtubules that would be required in each cell and the need for them to interact in a concerted fashion across large areas of the brain to generate conscious events: "He hasn't the faintest idea how they would do this. We can't prove at present that this is impossible but it looks highly implausible.

Roger is a theoretical scientist of some calibre and certainly of some considerable originality. He cannot be brushed aside as another nut, of which there are plenty. But his theory is based on one weak argument after another and personally I'm fed up with it," he says laughing.

He is undecided as to whether to let the matter drop or coauthor a scientific paper to reject Penrose's claims. The situation is psychologically fraught. "If we could persuade Roger that he was wrong then it would be worth doing. But if he is not going to admit that it's all highly unlikely Q and that is what wrong means in science Q then we would be wasting our time." He wants to talk to colleagues, especially Patricia Churchland, director of the experimental philosophy lab, University of California, who slammed Penrose's theories at Tucson as a waste of her lab time, before deciding what to do.

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Another hot topic at the Tucson conference was philosopher David Chalmers's proposal that there are two distinct aspects of the problem of consciousness that need to be addressed: how physical brain processes can lead to conscious events (the "easy " problem) and the nature of the subjective experience (the "hard" problem). Chalmers has been heavily criticised for promoting this division.

But Crick believes it useful to think of the problem along the lines proposed by Chalmers, although he points out that it has not been proved that the hard problem is a hard problem at all. "It is merely something that needs to be explained and Chalmers is quite right in saying that at the moment we do not see in principle how to explain it." But he adds: "Philosophers are not going to solve the problems by themselves whatever they may think. They haven't done it for 2000 years and there is no reason to suppose they will do it now. What they have to do is show us where our ideas are incoherent and they have to point to new types of experiments."

The philosopher John Searle, with whom Crick is in regular contact, is threatening to oblige. Searle has assured Crick and Koch that the way they think about the problem is completely wrong and he is going to prove it to them. "We shall see what we think about his arguments," Crick says smiling.

He has no doubt that current neuroscientific ideas about consciousness will need to be reformulated. One of his big hopes is that within the next few decades the subject will be transformed by the ability of molecular biologists to knock out certain genes in animals in such a way that particular types of nerve cells in the brain can be turned on or off. "I think it will become apparent that you will not solve the problem unless you get down to that level of detail of the nervous system. I think it will come. But it is not something I am likely to see Q I certainly can't rely on somebody doing it in the next few years. We have to think of other ways of approaching the problem."

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