After 12 years, a French team thinks they’ve arrived at a pretty good answer.

Neuroscientist Stanislas Dehaene presented his theory on the workings of consciousness Oct. 17 at the Hotel Ritz in Paris.

The presentation is worth watching if you’re interested in this kind of stuff, but here are some of the juicer excepts:

On how we (wrongly) envision consciousness:

In the past, the major problem was that people barely looked at the brain and tried to generate theories of consciousness from the top, based solely on their intuitions. Excellent physicists, for instance, tried to tell us that the brain is a quantum computer, and that consciousness will only be understood once we understand quantum computing and quantum gravity.

Consciousness as an “internal global workspace”:

In several experiments, we have contrasted directly what you can do subliminally and what you can only do consciously. Our results suggest that one very important difference is the time duration over which you can hold on to information. If information is subliminal, it enters the system, creates a temporary activation, but quickly dies out. It does so in the space of about one second, a little bit more perhaps depending on the experiments, but it dies out very fast anyway. This finding also provides an answer for people who think that subliminal images can be used in advertising, which is of course a gigantic myth. It’s not that subliminal images don’t have any impact, but their effect, in the very vast majority of experiments, is very short-lived. When you are conscious of information, however, you can hold on to it essentially for as long as you wish,. It is now in your working memory, and is now meta-stable. The claim is that conscious information is reverberating in your brain, and this reverberating state includes a self-stabilizing loop that keeps the information stable over a long duration. Think of repeating a telephone number. If you stop attending to it, you lose it. But as long as you attend to it, you can keep it in mind.

Our model proposes that this is really one of the main functions of consciousness: to provide an internal space where you can perform thought experiments, as it were, in an isolated way, detached from the external world. You can select a stimulus that comes from the outside world, and then lock it into this internal global workspace. You may stop other inputs from getting in, and play with this mental representation in your mind for as long as you wish.

And on where this theory could be in the future. (Warning: It’s really, really creepy.)

My feeling is that the future lies in being able to decode brain representations, not just detect them. Essentially all that I have told you today concerns the mere detection of processing that has gone all the way to a conscious level. The next step, which has already been achieved in several laboratories, is decoding which representation is retained in the subject’s mind. We need to know the content of a conscious representation, not just whether there is a conscious representation. This is no longer science fiction. Just two weeks ago, Evelyn Eger, who is a post doc in Andreas Kleinschmidt’s team in my laboratory, showed that you can take functional MRI images from the human brain and, by just looking at the pattern of activation in the parietal cortex, which relates to number processing, you can decode the number the person has in mind. If you take 200 voxels in this area, and look at which of them are active and which are inactive, you can construct a machine-learning device that decodes which number is being held in memory.

I should probably say quite explicitly that this use of the verb “decode” is an exaggeration. All you can do at the moment is achieve a better-than-chance inference about the memorized number. It does not mean that we are reading the subject’s mind on every trial. It merely means that, whereas chance would be 50 percent for deciding between two digits, we manage to achieve 60 or 70 percent. That’s not so bad, actually. It’s a significant finding, which means that there is a cerebral code for number, and that we now understand a little bit more about that code.

I believe that the future of neuro-imaging lies in decoding a sequence of mental states, trying to see what William James called the stream of consciousness. We should not just decode a single image, but a succession of images. If we could literally see this stream, it would become even easier, without even stimulating the subject, to see that he is conscious because such a stream is present in his brain. Don’t mistake me, though. There is a clear difference between what we have been able to do — discover signatures of consciousness — and what I hope that we will be able to do in the future — decode conscious states. The latter remains very speculative. I just hope that we will eventually get there. However, it is already a fact that we can experiment on consciousness and obtain a lot of information about the kind of brain state that underlies it.