It's fascinating to hear you say that at some point, we'll have to consider the question of whether bacteria are conscious. The assumption is that you need a mind to be conscious and bacteria don't have minds.
Koch: That's correct. Therefore, bacteria are probably not conscious. However, right now it's a guessing game. Most people say bugs are just little machines, but if you look at bees, they're amazingly complex. They can recognize single faces. And how they find a nesting site when they swarm in the spring is very complex behavior. How do we know it doesn't feel like something to be a bee? It's not that bees will have as elaborate minds as we have, but we cannot rule out at this time that it doesn't feel like something to be a bee, or that they consciously smell the gold nectar of certain flowers.
You are searching for the neural correlates of consciousness. The challenge is not simply to find the hot spots in the brain that are active during certain mental activities, but actually to explain how neurons and synapses and chemical circuits generate conscious experiences. This is more than mapping correlations between brain activities and what people say they're thinking about, which we can already see to some degree with fMRI scans. Isn't the real challenge to explain how specific neural correlates are wired together to generate conscious experiences?
Koch: The challenge is to see why this activity that's in your visual brain gives rise to a picture of a cup of coffee in front of me, and other neural activity in the olfactory part of my brain gives rise to the smell of freshly brewed coffee. In both cases, neurons are firing. They look the same. They release a bunch of chemicals like sodium and potassium. Somewhere else, a similar neural activity gives rise to pain. But in another part of the brain, the cerebellum, similar neural activity doesn't give rise to anything. The cerebellum, which is like a little brain at the back of the cortex, contains three-quarters of all the cells in your brain, roughly 69 billion. If you lose the cerebellum, you won't be a ballet dancer or a rock climber anymore. You'll walk with a funny gait. You'll talk very strangely. But your consciousness is only mildly impaired, if at all. So that implies that some types of neural activity are privileged. Certain parts of the brain seem to have a much closer association with consciousness than others. We have to understand what type of activity, what type of circuit, gives rise to conscious sensation.
I know a lot of neuroscientists get very excited about fMRI, but it sounds like the current state of technology is actually a fairly blunt instrument for trying to figure out what's going on in the brain.
Koch: It's a wonderful instrument because it allows us to peer inside your brain safely, but it's also very blunt. Remember, each cubic millimeter of the brain has a hundred thousand cells. So if I take the volume of brain that would be the size of a grain of rice, it contains about a half a million different nerve cells, and maybe seven miles of cable. It's very, very complicated. Yet in fMRI, all you can see clearly is this one box as a single point. But we know this one point contains half a million neurons, some of which may fire, but most of which don't fire. Some might fire less, some might fire more or fire in a very complicated pattern. But fMRI can't see any of that. It can just see the part of the brain that's active or the part that's suppressed. So fMRI is a wonderful tool, but it is very, very crude.
We are only now beginning to realize the complexity of it all. Over the last ten years, we realized there might be a thousand different cell types. They all have highly specialized jobs to do. They look different. They have different chemicals. They use different neurotransmitters. They have different genes encoding for them. They are wired up in a very distinct manner. So it's a little bit like having 86 billion tiles, but they come in sets of a thousand different colors and shapes. They all fit in very specific ways. And now, the big challenge is trying to unravel all of that and see the amazingly specific way that tile number 55 only talks to tile 255 and 972. And it inhibits tile number 17 and 31, and it doesn't talk to any of the other ones. That's what it's beginning to look like. So how does anxiety or sadness or the color blue emerge out of all of that?
There are plenty of very smart scientists and philosophers who say we will never crack the fundamental mystery of how matter turns into mental experience. For instance, the philosopher David Chalmers has talked about the "hard problem of consciousness." He says subjective experience is fundamentally different from what biology and physics can tell us. And he believes that science will never be able to bridge this divide between mind and matter. Do you disagree?
Consciousness is not easy to define, but don't worry too much about the definition.
Koch: Well, if you look at the historical record of philosophers, it's pretty disastrous. This is little acknowledged. Lots of people from 150 years ago said the same thing about life: "You shall never understand what life is. It requires a special force, élan vital." It didn't turn out to be true. The laws of physics describe life. Roughly 200 years ago, famous philosophers said we'll never know what stars are made of. That was 20 years before they discovered spectroscopy, and of course they realized you can analyze the elements out of which stars are made. So I'm profoundly skeptical when philosophers tell us, once again, what we'll never know. Science has a spectacular record of understanding the universe. Yes, right now it's a hard problem. For its size, the brain is by far the most complex system in the known universe. There's no guarantee that we'll understand it. Our cognitive apparatus just might not be up to it, but in principle I don't see any reason why we should be unable to understand it. Just because some philosopher doesn't get it doesn't mean we shall never know this. It's ridiculous. But a lot of people are very happy about that message because, for various reasons, they don't really want to understand things in the way science does.
David Chalmers has also suggested that consciousness may be a fundamental property in itself, not reducible to the laws of physics. What do you think of this idea?
Koch: This is an old idea, which I'm quite sympathetic to. Just like physicists in the 16th century realized that magnets have this weird property of attracting other magnets or pieces of metal. This is an invisible force. We realized our description of the universe wasn't complete and we had to include magnetic fields. To understand the universe, we say there's space, time, matter, and energy. It may well be that to fully understand consciousness, there is something equally fundamental: experience. I think a particular type of complex system, which of course needs to be defined, will have conscious experience. That's just the way the universe is, just like there's matter. In this hypothesis, we live in a universe that has this fundamental property of consciousness.
Isn't this called "panpsychism," the idea that all matter is sentient to some degree?
Koch: They're related but not strictly equivalent. From this hypothesis, it's easy to say that all matter has some consciousness associated with it, but very complicated pieces of matter like your brain, or, to a lesser extent the brain of a dog, or to a much lesser extent the brain of a bee, are complex systems with various degrees of consciousness. You could say even the worm and the fly have a little bit of consciousness, although it might be much less consciousness than you have in your deep sleep, which is not a lot.
I'm guessing that you're pretty unusual in suggesting that consciousness might be a fundamental property of nature, along with the laws of physics. Do many other neuroscientists think this?
Koch: No. Most biologists don't think about it. It makes them feel very uncomfortable thinking about these issues. But I think that's silly. We have to explain where consciousness comes from. There are two possibilities. One is as an emergent property. Small brains don't have it. Large brains have it. It's like the wetness of water. One molecule of H2O isn't wet. Two molecules aren't wet. But you put a whole bunch together, like in my cup of coffee here, and you get a wet liquid. Water is the quintessential emergent property. There are many other emergent properties in the world around us -- for example, democracy. One or two people don't have democracy, but in certain types of organization you get this emergent phenomenon called democracy. The claim of consciousness is of that ilk. I used to believe that, but I've been studying it now for 25 years, and consciousness is so strange. It's different from anything else because it has a subjective aspect. I don't think it's an emergent property. A much more elegant theory is that certain types of complex systems are conscious, and what type of consciousness they have depends exactly on the complexity of the systems.
I was surprised to see your book invoke Pierre Teilhard de Chardin, the Jesuit priest and paleontologist who believed the universe is becoming more conscious as it gets more complex. Most scientists write off Teilhard as a religious apologist.
Koch: Most scientists don't even know about him. He had this idea about evolution where he argued that from very simple micro molecules to single cell organisms to multi-cell organisms to simple animals to complex animals to us is the emergence of complexity. He observed that the universe was getting more and more complex, and he postulated this would continue. Essentially, he postulated something like the Internet. He called it the "noosphere" -- the sphere of knowledge that covers the entire planet and is heavily interconnected. He died in 1955, long before any of this emerged, and he postulated that human society would evolve into a very complicated entity that would become self-conscious. He thought this would happen on other planets and throughout the entire universe, and the universe in some weird state would become self-conscious. It's all totally speculative, but I do like some of these ideas. I see a universe that's conducive to the formation of stable molecules and to life. And I do believe complexity is associated with consciousness. Therefore, we seem to live in a universe that's particularly conducive to the emergence of consciousness. That's why I call myself a "romantic reductionist."