On Fear, Emotions, and Memory: An Interview with Dr. Joseph LeDoux


Humans are the only animals that can imagine the future. That’s great when it comes to figuring out what makes us happy. But what about those sleepless nights filled with anxiety?

Joseph LeDoux has spent 30 years studying the biological underpinnings of memory and emotion, especially the mechanisms of fear. He has been doing research on animals, primarily rats, to understand pathological fear and anxiety in humans.

The Amygdaloids (Daniela Schiller, Joseph LeDoux, Amanda Thorpe) at the Williamsburg Waterfront.

A Henry and Lucy Moses Professor of Science and professor of neural science and psychology at New York University, his concentration on the amygdala, that almond-shaped structure in the brain’s temporal lobe having to do with emotional behavior, has also spawned a rock band called the Amygdaloids, with himself and three of his scientific colleagues.

These days, LeDoux is looking at things differently. During a visit we paid the professor at this NYU office, the director of the Emotional Brain Institute and author of the bestselling books — “The Emotional Brain: The Mysterious Underpinnings of Emotional Life” and “Synaptic Self: How Our Brains Become Who We Are” — shared his latest epiphanies.

Brain World: You’ve been studying fear and emotion a good many years …

Joseph LeDoux: After 30 years, I’ve decided that I haven’t been studying fear or emotion at all. This is an issue within the field — exactly what emotions are. Some people say, “How can you study emotions in rats, because you don’t know what rats feel.” I say, “I’m not studying feeling. I’m studying the way the rat brain detects and responds to danger.” But I called the circuits “fear circuits.”

Lately I’ve been re-evaluating. If you think about what an animal does in a situation of danger, it does something to protect itself, either by remaining motionless or moving away from the harm. When a person is in that state, they do the same sorts of things. But they also feel afraid. So it’s natural to assume that when a rat is doing those things, it’s probably feeling some sort of fear as well. But if you follow the logical conclusion of all of this, you will see that even bacteria do these things. They’re in their little petri dish in a lab. If you put some acid on one side, they all move to the other side.

Obviously there are a lot of differences between bacteria, rats, and people, but what we’re looking at here is a survival function. Bacteria do all sorts of things that we do to stay alive. In addition to responding to danger, they acquire nutrients, balance fluids between their inner and outer environment, and reproduce to keep their species going. These are survival functions, and as evolution went from single-cell to multicellular organisms, the fundamental life force of staying alive still required defense against danger, sufficient nutrients and energy, balancing of fluids, thermoregulation, and reproduction.

I don’t think these systems are in the brain to create emotions. They’re in there to deal with the environment. But when you put one of those systems in a brain that has other capacities such as self-reflection and an awareness of its other activities, then you get emotions.

BW: The research you’re doing with rats deals with defense rather than fear. Does that change the implications of the work?

JL: Let’s call it “defense.” And it doesn’t change the implications. The problem is my students feel that their work is going to be thought less significant if it’s not about “fear.” But the truth is, the defense system is still contributing to emotion — to fear — the same way. We’re just calling it defense rather than fear, because fear, I think, is something else. It’s a matter of how we conceptualize it. I think that’s important, because if we don’t think clearly about these things, then we run around with loose ideas, and if you look at papers in the field on emotion, nobody really says what emotion is, they just study it.

BW: What’s the difference between an emotion and a feeling?

JL: There probably isn’t a difference. In fact, emotions and feelings have traditionally been thought of as the same thing. We’ve jumped through hoops to try and find ways to talk about emotions in animals. For example, Antonio Damasio and I have said that emotions are the unconscious part of fear and that the feeling of fear is a consequence of activating that emotion. But it’s kind of like making a square peg fit in a round hole.

What I’m now saying is that emotions are conscious experiences that occur when we find our self in a situation where a challenge or opportunity exist. Some occur when a survival circuit is active — like fear — while others don’t involve survival circuits — like pride. What defines the emotion is not whether there’s a survival circuit that’s active but whether we interpret the situation we’re in as either challenging or potentially beneficial. I’m putting all the emotions on a level playing field, but I am playing on a different field. I’m not studying emotion. I’m studying the function of survival circuits. Survival circuits contribute to emotions but are not emotion circuits.

BW: So you’ve been studying survival in rats …

JL: That’s my aha! moment. If we want to understand emotions, feelings, we have to study humans. Do animals have mental states? We don’t know, and we can never know for sure. Some people argue that we can interpret that from their behavior. But we can’t, really. If we could, then we’d have to interpret on the basis of bacteria’s behavior as well. So if you’re willing to say that emotions are in bacteria, that’s fine. But if you aren’t going to call it that, then we have to figure out why behavior is useful in saying a rat is afraid when it responds to danger and not in saying that bacteria are afraid when they do that.

Many people say that rats are closer to people, so they probably have something like human feelings. But what about a lizard? They have a similar brain to ours — all vertebrates do. Where do you draw the line? Fish, bugs, worms? My philosophy of doing science is that I want something solid. I prefer to try to study survival in the rat. I think from the point of view of doing research it makes sense to try and learn as much as you can without assuming mental states. Then maybe at some point we’ll have to come to terms with it, but I don’t think we’re at that point yet.

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