Science of Consciousness
September 22, 2004
Professor Gerald Edelman
Consciousness is an aspect of existence that many of us take for granted. The world appears as a unified whole, with sights and sounds drifting seamlessly from one moment to the next. But, how do these conscious experiences arise? What areas of the brain are important? And, can science give us the answers?
Joining us today on Berkeley Groks to discuss the scientific exploration of consciousness is Prof. Gerald Edelman. Among his many roles, Prof. Edelman is director of the Neurosciences Institute, and Professor and Chair of the Department of Neurobiology at the Scripps Research Institute. He is the winner of the 1972 Nobel Prize in Physiology or Medicine for his work on the structural diversity of antibodies. And, he is the author of several books, including Neural Darwinism, The Remembered Present, and A Universe of Consciousness. His new book, Wider than the Sky: The Phenomenal Gift of Consciousness, explores the science of consciousness research for a general audience.
Prof. Gerald Edelman (GE) talks with Charles Lee (CL) about the science of consciousness.
CL: Consciousness is one of those interesting issues in science, but one that many think might not be amenable to scientific inquiry. Is consciousness amenable to scientific inquiry?
GE: The short answer is “Yes”. It’s true that until recently it was the province mainly of philosophers, and not of scientists. That situation has changed to some degree because of technical improvements in being able to record electrical activity in the brain in a non-invasive fashion by various electrical tricks and thanks to physics. So we now have a position where we can perhaps study the neural correlates of consciousness, which a number of people are now doing quite vigorously.
CL: And, what are the methods that people have been using to address brain function and consciousness?
GE: There are mainly two methods, although there are a number of others. But, the two methods are functional magnetic resonance imaging (fMRI) and the second is magnetoencephalography. The first measures the blood flow changes that accompany neuronal changes in a living subject’s brain. The second one measures minute magnetic fields that are given out by the electrical currents that traverse inside neurons or nerve cells in the brain. The first one can measure the location of various centers of the brain as they are enacted and activated. And, the second can see in a very rapid manner what happens in time with the currents of the brain. So, right now we have to put both matter together to make sense of what is going on.
CL: So, one gives very high spatial resolution, and the other high temporal resolution?
CL: In your books, you talk about your theory of consciousness as, “The Theory of Neuronal Group Selection”.
GE: Well, let’s perhaps take this in steps. First of all, I believe the evidence supports the view that the brain is not in fact a digital computer. That the brain is in fact something that evolution has put together in terms of an incredible circuitry, which is capable of carrying out pattern recognition rather than logic. Of course, it can carry out logic in civilization after you train a person who has higher order consciousness. But, it’s not a logic machine first and foremost. It’s a pattern recognition device, and it has not been engineered it has been developed by natural selection.
The interesting thing is that if it’s not a computer and it foregoes logic and a clock, then how does it manage to keep everything together. Well, that’s what this Theory of Neuronal Group Selection, or Neural Darwinism, is about. It says that the brain develops incredible diversity of its circuits during actual embryonic development and later on in life. And secondly, it develops an arrangement at its synapses, or the connections from one nerve cell to another, in which these connections are strengthened or weakened, much like there was a traffic cop on a particular synapse saying, “You go here, and you go there.”
Now, what one has to explain is that the connectivity of the brain is simply stunning. For example, the cortex of the brain, that wrinkled structure you see in pictures of the human brain, if unfolded, would be about the size of a table napkin. It would have 30 billion neurons, and one million billion connections. If you just counted one connection per second or one synapse per second, you would just finish counting 32 million years later. If you calculate the number of possible paths, it’s 10 followed by millions of zeroes. There are 10 followed by perhaps 83 zeroes number of particles in the known universe. So, it gives you respect for what evolution can do.
And, this Theory of Neural Darwinism is suppose to explain how that diversity plays in to your recognition of the world. And, the way it does is it has a huge number of repertoires of variance. Those that match are reinforced in their synaptic connections, and those that don’t match are diminished. Well, this means that everybody’s brain is quite unique. No two brains are alike, even identical twins.
Finally, there is a complex process called reentry, in which there are massively parallel, reciprocal connections amongst brain areas. And, a process of electrical stimulation across these various areas couples the maps of the brain together. So, they all act together. Now, that process of reentry, according to the theory, is said to be the origin of consciousness in a part of your brain that connects to the cortex called the thalamus, which is the way station that connects all of your sensory elements, except for smell, directly to the cortex. The thalamocortical system has a huge connectivity, and it is considered to be essential and required for consciousness through this process of reentry.
CL: So, selection of these various neural circuits via this process of reentry gives rise to the various conscious experiences?
GE: Yes. So, let’s say, what did evolution do? Well, somewhere along the line, perhaps 25 million years ago, circuitry was developed during development in which the thalamocortical connectivity was established back and forth in a reentrant fashion. And, what that did was allow an animal with that brain to carry out an incredible number of different discriminations, what you might call “qualia”. In fact, what the philosophers call “qualia”, the greenness of green and the redness of red, I think is a little too constricted. I believe that qualia are all the states you are experiencing and not experiencing now. Those qualia are those discriminations. So, effectively speaking, the thalamocortical core, or dynamic core as we call it, is responsible for giving rise to all these incredible numbers of discriminations. And, qualia are the discriminations. Obviously, an animal that could discriminate in this fashion would have a selective advantage and be selected in evolution.
CL: As you mention in your book, can different neuronal populations give rise to the same qualia?
GE: Oh yes. That’s a very interesting concept. One that people again find a little unfamiliar, and that is called “degeneracy”. I can give one example that might make it clear. And, I will use the genetic code, and then I will go back to neurons. The genetic code is a degenerate code. There are twenty amino acids that make up a protein. And, coding for each one is a particular set of triplet nucleotide bases of DNA and RNA. There are four different kinds, G, T, A, and C. And, any three of those can form 64 different triplet codons. So, if you have 64 coding for 20 amino acids, it turns out that the third position of each triplet can have nearly any nucleotide and it will still be coding for the same amino acid. So, if you now imagine three hundred or so of these nucleotides strung together, a hundred triplet codons for a hundred amino acids in a row in a protein, the number of possible sequences in which you’ve changed every third position, means there’s a huge number of different nucleotide strings that will specify the same amino acid protein string. That is a typical case of degeneracy, in which different structures give rise to the same output or function.
CL: And, this motif is carried out throughout biology?
GE: That’s really quite prominent in all of biology, but especially in the neuronal circuits of this dynamic thalamocortical core, in which there are many different structural circuits that will yield the same outcome.
CL: So, would this imply that different structures in different brains could give rise to the same outcome?
GE: Absolutely, well said. It is a striking fact, and a non-trivial one, that your brain and my brain will be unique in the history of the universe.
CL: So, previously on the program, we talked with Prof. Christof Koch, who along with the late Prof. Francis Crick, are also involved in consciouness research. And, their approach appears to be at a finer scale than the global approach that you take.
GE: Well, I think what happened is that Crick particularly became convinced that the way one can approach consciousness is through visual consciousness, and looking at the detailed visual circuits of the brain. His colleague Koch and he were pursuing that line. I wouldn’t say that my view is more global, or that theirs is more particular. In fact Crick visited me several times in the last eight months or so before his recent death, alas. And, he and I came to an agreement that what he and Koch called “coalitions” are the same as the states of what I call the “dynamic core”. So, the essential ideas are very close, but they tend to emphasize visual consciousness, where I include all the other sensory orders and the higher order consciousness.
I make a distinction for example between what I call primary consciousness, which is the ability to create a scene or all these complex discriminations in what I call “the remembered present”, right now. And, not until you have animals that have semantic capabilities, and in our case, true language, do you get higher order consciousness. If you have higher order consciousness, you can do what an animal that has only primary consciousness can’t do. You can have concepts of the past and the future, and you can develop a social self through language. Animals clearly, although we can’t absolutely prove this, are conscious, but have only primary consciousness. Our consciousness allows us to be conscious of being conscious.
CL: You mention that the science of consciousness must rely on human subjects because of the reporting ability of humans.
GE: Yes, well asked. That I think is quite important, because if you do experiments on a human being, you can get a report. And, if you set up your experiment in such a way that the subject doesn’t know the setup, and you have three or four different experimental arrangements, and they all converge on report, then you can be pretty sure that it is a result of a conscious act on the part of the subject. It’s a little harder when you do it with monkeys and dogs. It can be done with so-called “catch trials” in monkeys, as has been done by Logothetis in Germany. But, the human gives you the reasonable confidence that since the person doesn’t know how you’re designing your experiment, that your results if they converge are not a miracle but really the result of a conscious effort on his part.
CL: Is there an effort to merge both the human and animal studies?
GE: Oh yes. And, in fact, we have done that with these methods. For example, Logothetis has measured from the monkeys looking at a phenomenon known as binocular rivalry. I’ll give you an example. If I show you a red bar vertically and a green bar horizontally, and red and green lenses in your right and left eye, respectively, then your brain can’t fuse those two discordant images. So, what happens is first you see the red vertical then you see the green horizontal. Well, a variant was done by Logothetis on monkeys, and what he saw was in the visual cortex was everything responded to the signal. But, in the higher order cortex to which it connected, the so-called inferotemporal region, the response of the neurons was to the percept of the monkey. Now, the monkey couldn’t report directly, but he had ways of checking. We’ve done the same experiment in humans with magnetoencephalography, where the human can report and press a button when they’re conscious and when they’re not. And, we find that there’s a huge explosion of reentry all over the brain when the person becomes conscious of one of those bars. So, there’s a concordance between these two neuronal correlates of consciousness between the monkey and the human.
CL: I’m curious what do you think will be required for a true scientific explanation of consciousness?
GE: Well, of course, we want to accumulate more examples of neural correlates of consciousness to explain its properties. Why it’s unitary, that is why you have the whole impression. Your hearing, smell, and seeing make one whole picture, yet that picture changes from time to time. You want to explain why consciousness has intentionality, why for the most part it’s about things. And, I think that’s because it’s about perception as well. And, you want to explain matters like qualia.
So, there are two tasks I think. One is to clarify these issues, and find neural correlates of consciousness of the kind I talked about. And, the second is to make sure that you are clear in your logic and thinking. For example, I think there is an advance in realizing that what consciousness gives, as a result of evolution, is the ability to make higher order discriminations which are adaptive, and that qualia are those discriminations. So, if you get the logic and the science together, there would be one really fantastic outcome that would really convince us, and that would be if we could build a conscious artifact, if you could actually put together with these ideas something that you could verify is conscious. Now, the implication there is that it would have to have some kind of language to just what I talked about with respect to report. When that happens, some people will be thrilled and some people will be horrified, but I think we’ll have a confident notion that we really begin to understand this fascinating subject.
CL: More philosophically, how long do you think it will be before we have such an understanding?
GE: Oh dear. Predictions of the future are hazardous even in science. You can be sure that sooner or later that as we understand this subject it will come to pass, because it has always been the case in scientific issues. I’m working by induction here, but every time science has found a principle, engineering has found a way to realize it.
CL: Well, I guess we’ll just have to wait and see.
GE: Yes, we will. You can come and visit my mausoleum.
CL: Indeed. Prof. Edelman, I would like to thank you for very much for joining us on Berkeley Groks, for a fascinating discussion, and for discussing the ideas in your book, Wider than the Sky: The Phenomenal Gift of Consciousness.
GE: Thank you. I appreciate the time.