NOVA Online | Secrets of the Mind

What is the nature of consciousness? Is it limited to humans? Does free will exist? Read on for one scientist's view.

The Electric Brain

How does a three-pound mass of wet gray tissue (the brain) succeed in representing the external world so beautifully? In this interview with noted neuroscientist Rodolfo Llinás of the New York University School of Medicine, find out how the rhythm of electrical oscillations in the brain gives rise to consciousness, and how failures in this rhythm can lead to a variety of brain disorders.

NOVA: Let's start by talking about why one needs a nervous system—or a brain—in the first place.

Llinás: That's a very intriguing issue. The nervous system is about 550 million years old, and it first came about when cells decided to make animals. Basically there are two types of animals: animals, and animals that have no brains; they are called plants. They don't need a nervous system because they don't move actively, they don't pull up their roots and run in a forest fire! Anything that moves actively requires a nervous system; otherwise it would come to a quick death.

NOVA: Why would it die if it didn't have a nervous system?

Llinás: Because if you move, the variety of environments that you find is very large. So if you happen to be a plant you have to worry only about the very small space you grow into. You don't have to do anything other than maybe move up and down. And you're following the sun anyhow, so there is no planned movement, and therefore there is no necessity to predict what is going to happen if, which is what the nervous system seems to be about. It seems to be about moving in a more or less intelligent way. The more elaborate the system, the more intelligent the movement.

NOVA: So you need a nervous system in order to be able to predict the future?

Llinás: Yes, and in order to predict you have to have, at the very least, a simple image inside that tells you something about the purpose of the outside world. That is common to all nervous systems of all forms that we know of. Each animal has a different universe—the universe it sees, the universe it feels, the universe it tastes. Earth probably looks very different not only for all of us as individual humans, but also for different animals.

NOVA: How does consciousness come into this view of the brain? Is consciousness a mysterious phenomenon, in your opinion?

"We assume we have free will, but we don't."

Llinás: I don't think so. I think consciousness is the sum of perceptions, which you must put together as a single event. I seriously believe that consciousness does not belong only to humans; it belongs to probably all forms of life that have a nervous system. The issue is the level of consciousness. Maybe in the very primitive animals, in which cells did not have a single systemic property—in which each cell was a little island, if you wish—there may not have been consciousness, just primitive sensation, or irritability, and primitive movement. But as soon as cells talked to one another there would be a consensus. This is basically what consciousness is about—putting all this relevant stuff there is outside one's head inside, making an image with it, and deciding what to do. In order to make a decision you have to have a consensus.

This colored scanning electron micrograph shows the synapses, or connections, between two nerve fibers (in purple) and a nerve cell (yellow). The picture is magnified 10,000 times.

NOVA: But it all just boils down to cells talking to one another?

Llinás: Some people believe we are something beyond neurons, but of course we are not. We are just the sum total of the activity of neurons. We assume that we have free will and that we make decisions, but we don't. Neurons do. We decide that this sum total driving us is a decision we have made for ourselves. But it is not.

NOVA: So this mass of wet gray tissue that is our brain is made up of neurons?

Llinás: The brain is made out of cells. It is a long and very distinguished group of cells—about 550 million years or so old. These cells have a small mass. Our brain is about one-and-a-half liters, or three pounds, but it has 10¹⁰ cells, which is a huge number of cells. Ten billion cells. And each cell has 1,000 to 10,000 or so synapses—the connections between the cells. So the brain has trillions of synapses.

NOVA: How does the brain keep all these different neurons communicating in synch?

"Neurons like one another very much. They basically chat all day."

Llinás: Neurons like one another very much. They respond to one another's messages, so they basically chat all day, like people do in society. "Where can I park?" "How much is it going to cost?" "Am I going to get a ticket?" One set of neurons talks to another set of neurons, and they talk back, so we have a dialogue between different components in the brain. And the dialogue is not between one cell and another cell, but rather between many cells and many other cells. It's like having a huge number of people holding hands, dancing together, making ever-changing circles and organized together in such a way that every cell belongs, at some time, to some circle. It's like a huge square dance. Each dancer belongs to a particular movement at a particular time.

NOVA: And there's music that keeps them all dancing together?

Llinás: Right. It's generated by the neurons themselves. Neurons have an intrinsic rhythm, a bit like a hum. They generate this electrical dance at a given frequency because they have similar rhythms—they hum in unison. But as in the case of choirs and dancing, you can have two groups doing different things at the same time. Now imagine that each group doing something represents an aspect of an external event, like a color.

Scientists have recorded the "hum" of neurons communicating. This movie shows the response of cells in the cortex to a visual stimulus.

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NOVA: That's the brain's job—to represent an external event?

Llinás: Right. Imagine many cells making an activity circle, with electrical activity going around and around like a windmill. Imagine that out of this circle come a few cells into the center and perform a particular dance that the other cells see but are not necessarily part of. Now these cells that do this particular dance may be cells that have learned something from the outside that they want to put in the context of whatever else is happening in the nervous system. The brain, when awake, is continually generating a picture of the outside world. When new information from the outside comes in it has to be put into context with whatever else was happening just before.

NOVA: Is there ever nothing going on—no dance—inside the brain?

Llinás: Sometimes there is nothing as far as consciousness going on, like when you fall asleep. At that time you are not generated. That particular dance, that is you, is not being created by the brain at the moment. If you are asleep but dreaming then the brain makes another dance during which you exist but you don't care about the external world. You can exist on your own with dreams, hallucinations, or deep thoughts, or you can relate to the outside world. Normal people want to relate to the outside world. If you happen to be a schizophrenic you may not. You may want to hallucinate somewhere in a corner. You are consumed by your thoughts. You are fascinated by whatever is inside your head.

NOVA: What part of the brain does this coordinating? We've all heard of different areas. Frontal lobes do this, another area does that....

Llinás: If we look at the nervous system there are basically two functions. One is sensory—the ability to respond to the outside world—and the other is the ability to do something about it, the ability to modify the world. As the nervous system gets more complex in higher animals there's another totally astounding property, which is the ability of the nervous system to invent things inside the head, which it can then make into reality. All my life, even as a child, I have been amazed that you can think of something that doesn't exist and then by using the motor system—painting, talking, constructing—you can make them be part of the external world.

NOVA: Make a pie, for example.

The brain is the ultimate organ. It can make a reality. It can dream it.

Llinás: Make a pie that didn't exist before. So it gives you an idea of the unbelievable ability of the system. Not only can it see or move, but it can also make a reality. It can dream it. From that point of view, it really is the ultimate organ. Each part of the brain has a particular function with respect to the nervous system. The visual cortex has one function, the frontal lobes have another function, the auditory system has yet another function. And yet when we look at the external world we see things as having properties that are inseparable from the object itself.

NOVA: Can you give us an example?

Llinás: Imagine I have a little bird on my hand. I can see the bird. I can see its color. I can see its shape. I can hear it sing. I can feel its weight on my hand. It might peck me. All of these things occur simultaneously, so we say that the bird has those properties. But all those properties are put together in different parts of the brain. So one wonders how the brain makes a collage of all these sensory inputs to generate one single precept—the bird—out of all the different sensory systems activated. This is called the binding property. Since we don't know for sure how it works, we call it the binding problem.

Our experience of a bird is made up of many different sensory inputs, including color, sound, smell, and touch. How does the brain put all this information together simultaneously?

We are not sure exactly how it happens, but there are good ideas about how it may happen. One of the ways we can attempt to understand how it happens is by studying people who have mental or neurological problems. Someone with a lesion on his or her visual cortex would be able to hear and feel and move but would not be able to see, so you know that he or she injured the conscious component that sees but not the other conscious components. So consciousness has parts.

Continue: How else can consciousness get damaged?

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