PAUL GROBSTEIN
DEPARTMENT OF BIOLOGY
BRYN MAWR COLLEGE
BRYN MAWR, PENNSYLVANIA 19010
(610) 526-5098 pgrobste@cc.brynmawr.edu
I became a scientist more or less by default. I thought it was the kind of job that would put the least demands on me, and hence give me the most time to watch, explore, imagine, dream, and follow my nose into the questions I was actually curious about. Even after I started working on the brain. I was skeptical that I would ever actually learn anything from doing so that I really cared about: I thought it unlikely that thinking about a single thing, even the brain, could matter very much. I was wrong, twice. Scientific research is not, in fact, an undemanding job, and once I understood this I realized that if I was going to do it, I had better do it on something I cared about. As it turned out, thinking about the brain is actually a pretty good way to get at some of those big questions that really interested me and most people, I suspect.
I was wrong about another relevant thing. (Being wrong and learning to value that is a second aspect of science which many people don't understand.) Shortly after I got my Ph.D., I wrote an article of which I was enormously proud. "Western scientific tradition,'' I wrote, "recognizes two sources for the adaptiveness characteristic of living organisms. On the one hand, there is the genome, which can be thought of as a summary of many generations of previous experience in dealing with the environment. On the other hand, there is the individual experience of an organism, information acquired within his (or her) own lifetime. These two information sources - the genetic and the ontogenetic - interact during the development of the organism.'' Well, it turns out it is just not so. There is genetic information and there are the experiences one has with one's environment, but there is also a third thing. In order to understand it, you need to know something about the brain.
Let's start with genetic information, or actually with a much older and perhaps even more interesting idea, that of ''innate'' information. Humans have always felt that they "know'' things independently of any experience they ever had. Perhaps the greatest single insight biology has to offer is that the intuition is not only almost certainly true. but also clearly understandable in concrete terms; it does not require a belief in the mystic or the supernatural. The behavior of all organisms, humans included, reflects information over and above that which they have collected in their own lifetimes: they are born with a vast storehouse of genetic information, the product of uncountable generations of their ancestors' experiences with the world.
This understanding is a relatively recent one, for reasons both scientific and social. The questions scientists ask can create ideas and feelings significant in other realms of human activity, but the reverse often happens. The eighteenth and nineteenth centuries, at least in the Western world, were a period of revolutionary thinking about individual human potential, of reaction against the notion that one was born and stayed forevermore a serf, or a king, or an idiot who must remain for life locked in an insane asylum. The key observation was that by altering a person's experiences one could in fact alter how he or she acted, who that person was and became. In this context, much of philosophy, psychology, and what came to be neurobiology became preoccupied with understanding how experiences affect one, and the concept of the innate fell very much out of fashion.
The pendulum began swinging back in the late nineteenth century, but even now the reality of the innate is not fully appreciated by most people. A number of observations in biology and neurobiology contributed. Among the most important was a set of experiments on amphibians (salamanders and frogs) reported by Roger Sperry in the 1940s. These organisms make rapid movements directed toward prey items (flies, worms, and whatnot) in their vicinity.
Sperry was interested in how they knew the right movement to make for a prey item at any given location. He already knew that each location in space is seen by a different location on the retina (a piece of the nervous system covering the back of the eye), that each different location on the retina is connected by the optic nerve to a different location in the brain, and that each of these different locations in the brain causes a different movement. In a normal animal, the pattern of connections between eye and brain is highly and appropriately ordered: a retinal region which sees in a particular direction is connected to a tectal region which causes a movement in that direction. In an important sense, then, the pattern of connections between the eye and the brain represents the animal's knowledge of what movement to make for a prey item at a given location. What Sperry wanted to know is whether this pattern of connections is or is not the result of the animal's experiences.
To answer this question, Sperry took advantage of the fact that in amphibians, the optic nerve will regrow after it has been interrupted. (Why this is true for amphibians and not for people is an interesting and unanswered question.) Sperry cut the optic nerve and simultaneously rotated the eye 180 degrees in the eye socket, so that retinal locations which had been looking forward were now looking behind, and those looking behind were now looking forward. If the pattern of connections between eye and brain was based on experience. on 'learning" what movement to make for a prey item at a given location. then during regeneration, the part of the retina now looking forward should connect to the part of the brain which causes forward movement. and the part now looking backward should connect to the part of the brain which causes the animal to turn around; the animal's behavior should be normal. What Sperry found. in contrast. was that his animals responded to prey items in front by turning around and to prey items behind by moving forward. and kept doing this even though they never succeeded in reaching the prey. In short, the connections between retina and brain were remade exactly as they had been before. rather than the way experience would show they should be made. The conclusion from this (and some supporting experiments) is that the pattern of connections between retina and tectum, and the information they repre- sent about what movement to make for a stimulus at a given location, does not reflect an animal's experience. It is innate.
Sperry experiments were an elegant demonstration that experience cannot be the source of at least some of the information in the nervous system; a host of subsequent experiments in a variety of organisms have now made it clear that the case he explored is far from an exception. Showing that information is not the result of experience is not quite the same thing as showing that the information is genetic, but here too there exists a large array of relevant observations, in which one observes similarities and differences in behavior between organisms with similar and different genomes (for example, a study of identical twins reared apart reported recently in the popular press). The conclusion from all of this is that the genome is a potent source of information influencing the behavior of all organisms, humans included.
Many people find this conclusion distressing, so it is worth pausing a bit to consider what it does and doesn't mean. I've been careful to say,"influencing" behavior, rather than "determining'' it, because that is the reality as it appears in neurobiological research, not coincidentally, as most people feel it themselves. What one becomes is influenced by what one is when one is born. What one becomes is not determined by it. One's subsequent experiences (and that mysterious third factor I'll come to) also play significant roles in how one behaves at any given time. We're not talking about genetic determinism here, but rather about genetic influences. There are also concerns that an acknowledgment of genetic influences somehow threatens the perception of oneself as a distinctive, unique individual. If one's genome is really significant in behavior, doesn't that mean that fundamentally we are all the same and should act the same? The answer is emphatically no. One of the significant things about genetic information is that, with the exception of identical twins, it is different in every individual. Each of us has a different and unique summary of the experiences of our ancestors. In short, the genome with which one is born is not something to be frightened of; it is something to value and cherish. It is a rich source of information about how to deal with the world which one gets for nothing and a distinctive birthright.
Given the present cultural and historical context, I don't feel a need to spend a lot of time persuading you that, in addition to your genome, the experiences you have with the world during your own lifetime are a significant influence on behavior. There are, however, some neurobiological aspects of this reality which are worth noting. The first is that for any experience you have with the world to produce subsequent effects on your behavior, it must first be detected and reported to your brain by your sensory nerves, of which the optic nerve mentioned earlier is one. The second is that this report must bring about some kind of more or less permanent change in how the brain works. There is currently a lot of interest in neurobiology in this step, and a rapidly increasing knowledge of the kinds of changes (there are lots of them) that can occur. The third, and perhaps the most interesting, is that even when one is thinking about how experience affects behavior, one can't forget the genome. It is clear that genetic information influences what one learns and how easily. Indeed, there is some intriguing evidence that at least in some cases, things that one finds difficult to learn may be so because they are in conflict with genetic information, and one has to in some sense unlearn the latter in order to learn the former.
So, there is the genome, and there is the information one collects during one's own life by interacting with the environment. And that brings us to the crux of the matter. Is that all there is, as I once thought'' If one knew everything there is to know about the genome of an individual. and everything there is to know about their experiences, everything reported by all the sensory nerves, could one predict their behavior? The answer, I'm now convinced, is no. There is a third source of information that influences the behavior of all individ- uals, something which is not in the genome and has never been in the sensory nerves. There is information which the brain makes up for itself.
There is, in the retina of each eye, a hole where the optic nerve leaves the back of the eyeball to go to the brain. The upshot is that when you look at the world, there is a small part of it which you don't actually see, the part at which the piece of the retina with a hole in it is looking. You can convince yourself of this with the figure in the margin. Hold the page sideways at arm's length with the dot to the right. Close your left eye, stare at the cross mark and move the page slowly toward you. At just the right distance, the dot will disappear because its image falls on the hole in your retina. Closer still and it reappears, as it moves off the hole again. What' s real ly important, though, is that you don't see a hole when the dot disappears. You see a white piece of paper. And if you did the same thing with a red or a blue piece of paper, you'd see a red piece of paper or a blue piece of paper. What you see in that place is not genetic information (it's different depending on what you're looking at), and it is not information about that place which is coming in on your optic nerve (there isn't any). It's made up, by your brain.
The same thing happens, more dramatically, when you dream, or daydream, or imagine, or think. You are seeing things, feeling things, having things happen to you, with no sign whatsoever of them in your sensory nerves. You are having experiences, but they are not experiences with the environment, with the real world. They are experiences your brain is making up for itself. Are they significant for your subsequent behavior? Of course they are. Dreams, daydreams, imaginations, idle thoughts very much alter how you relate to the world. They give you a wealth of information about yourself, about how you would or might relate to other things, which you can't get from your genome or from experiences with the real world. And it' s almost certainly information which no one else, no matter how well they knew your genome and the environment you grew up in, could possibly know you have. Among the most striking features of dreams, and of creative thought generally, is their unpredictable character. Elements of experiences you have actually had (and probably elements of genetic information as well) appear in dreams, but they are put together in odd, frequently apparently random ways. It's almost impossible to prove, but there is every indication that not only could no one else fully predict your dreams, but you couldn't either. You have, within yourself, an ability to make for yourself experiences no one else has ever had. and hence to see things no one else has ever seen and learn things no one else has ever learned.
So, that's what I've learned, so far, about things I care about. I hope you're persuaded that studying the brain does lead to some interesting ideas, or if you thought you knew all this already, to some concrete ways of demonstrating what you would like to think is true. It also may have occurred to you that a lot of this is particularly satisfying to me, since it gives me an argument to go on doing what I have always wanted to do anyhow: to follow my nose, imagine, and dream. There's a little more to it than that, so let me attempt to summarize the whole thing in a few pithy words that I hope arc better than those I wrote years ago: Believe in yourself (the genome's there to help), learn from your experiences (as everybody says), and (at least as important as the other two), let yourself dream.