JB: How does a Dan Dennett or a Steve Pinker relate to your work?

LEDOUX: In Pinker's recent talk, Organs of Computation, I noticed that he did talk about emotions; he was talking about how passions fit into the mind. I think we'd agree on a lot, say about the evolutionary aspects of emotions and their unconscious nature as processes in the mind. I'm more interested in how evolution has kept emotional systems the same in man and other animals, whereas he seems to be more interested in what makes the human brain capacity for language a unique function not present in other species. Where we'd probably differ the most is in how we approach the problem. I want to do it from the brain, so that I know that my theories are tied to the hardware in a biologically plausible way, but I think he wants to do it without depending on the brain. I think both approaches have their strengths and weaknesses, and both are needed.

What I talk about is compatible with Dennett's views in some ways, because I'm dealing with emotions not as conscious feelings but instead as computational functions of the nervous system. The way I talk about emotions puts them at the level of what some people in cognitive science call the sub-symbolic level. In this sense, emotional systems are among many systems that operate in parallel at an unconscious level. In Dennett's view, there's a symbolic system sitting on top of all these sub-symbolic systems. This is where consciousness comes from, loosely speaking.

The symbolic system has some access to the outputs of the unconscious emotion systems as well as all the other perceptual and other subsymbolic systems and the one that grabs hold of the symbolic system at the moment is what we are conscious of. So we can be conscious of emotional events or mundane events. So I'd say there's not a special system for emotional experience separate from other kinds of conscious experiences. There's one mechanism of consciousness and it can be occupied with mundane events or highly charged emotions. I think my view of the mind is not incompatible with Dennett's. That's not to say that I agree that Dennett's explained consciousness. Instead, I agree that most of the mind doesn't work through consciousness.

JB: How would you describe yourself?

LEDOUX: I was recently called a radical behaviorist disguised as a neuro-scientist. I thought that was an interesting twist. It's true that I try to deal with emotions as unconscious processes as far as I can, but I don't deny the importance of consciousness. I just think that it's gotten in the way in the study of emotions. I'm not really a radical behaviorist. I realize that I am simplifying and probably oversimplifying emotion to study it the way I do, but I hope to build up to complex issues from a solid understanding of the simple stuff rather than have to reach down from confusion to try and account for the simpler processes.

JB: Can you say more regarding the difference between repressed memory and a sub-symbolic system?

LEDOUX: There are several things that are important to pull into this topic. One is the newly emerging data on the effects of stress on memory. The basic finding is that in periods of intense stress the explicit memory functions of the temporal lobe memory system can break down. Stress is usually defined physiologically by the amount of so-called stress hormones from the adrenal gland. When this stuff is released it floats around in your blood stream and gets into the brain. The hippocampus and amygdala are targets. These hormones adversely affect the hippocampus. They make it very difficult, for example, to induce long-term potentiation in the hippocampus, so the hippocampus begins to shut down physiologically. Also, spatial learning is interfered with. If the stress continues, dendrites begin to shrivel up, and if the stress continues even longer the cells die and the hippocampus itself begins to shrink in size. Bruce McEwen and Robert Sapolsky have done a lot of this work on stress and the hippocampus. There have also been some recent studies of patients with post traumatic stress disorder, Vietnam vets, for example, who have a greatly reduced volume of their hippocampus, and they have all these memory disturbances.

In contrast, stress seems to potentiate the amygdala. Stress will make the amygdala do what it's doing but even better. Let's say you get mugged or raped. The stress system releases all of its hormones (probably as a result of the amygdala detecting the threat and activating the stress hormone system). The hormones get into the brain and the hippocampus is adversely affected to the point where it can't consciously form a memory of this experience. But your amygdala is potentiated, so it's not only forming a memory unconsciously, but it's doing it better than before. So the exact conditions that can lead to hippocampal memory impairment (an inability to form a conscious memory) can lead to a facilitation of unconscious emotional memories through the amygdala.

Now you're a person who's walking down the street with no conscious memory of having been traumatized. There are witnesses that tell you it happened but you deny it--there is in fact often denial in situations like this. You carry unconscious traumatic memories but no conscious understanding of what happened. I don't know that something like this actually happens, but the biology is very plausible. It's totally conceivable that someone can be traumatized in this way and have no conscious memory of it. I believe that. And it fits with all the science that we have about all of this.

Now the next question is, can you then, through psychological tricks, comforting, therapy, whatever, bring these memories back in a person who never had them? And the answer to that is a clear No. It's not possible to take a memory that was not coded through the hippocampus and turn it into a hippocampal memory. So the amygdala has its memory; it doesn't then share it with the hippocampus, because they do things differently. The amygdala does its business, the hippocampus does its business. They communicate with each other, but their coding and representation is different. So you can't just get information out of the amygdala and turn it into content that the hippocampus can read. I think this kind of work tells us a lot about the psychology of memory and emotion, not just the biological details.

JB: What do you want to accomplish in the next five years?

LEDOUX: I want to understand several aspects of emotion that we have very poor understanding of now. The first part we're beginning to understand pretty well, which is how the initial aspect of an emotional reaction is elicited. In other words, how you jump back from a bus as it's approaching, and only afterwards consciously realize that you've jumped back, and only then feel afraid. We understand that reactive system in pretty good detail. But what we don't understand is the system for emotional action. How do you voluntarily make decisions and control your emotional behavior once you've reacted in this unconscious way. What circuits in the brain are involved in what psychologists call coping, the cognitive and behavioral effects that follow the arousal of emotion and one's attempts to deal with emotional arousal? Probably the basal ganglia and cortex area involved. The question of what makes us emotional actors as well as reactors really interests me.

That takes us to another issue, which is where do conscious feelings come into emotions? How do we get a deeper understanding of emotional feelings? We all want to know where feelings come from and how they work. So much of the work in the past started with feelings and tried to back into the problem and didn't get anywhere, which is why I start at the bottom and work up to feelings. I also want to know a lot more about emotional memory. Most of the things that make us emotional are learned through experience. So a key part of an emotion system is how it learns and stores information. Overall, I would summarize all this by simply saying I want to try to understand more about cognitive-emotional interactions. We have to put emotion back into the brain and integrate it with cognitive systems. We shouldn't study emotion or cognition in isolation, but should study both as aspects of the mind in its brain.