JB: So what about feelings? What are they?
LEDOUX: The study of emotion has focused on conscious feelings almost to the exclusion of everything else. Emotion researchers, for some reason, seem to be carrying the burden of the mind-body problem on their shoulders. In other words, I think the problem of feelings is one and the same as the problem of consciousness, and that emotion researchers have no more or less of an obligation to solve this before anybody else. Take vision. Philosophers have worried about where the redness we experience comes from when we see an apple. But vision researchers figured out that they could study how we process red without having to first figure out how we experience red. The same can be done in the study of emotion. We can study how the brain detects and responds to danger, even if we don't know how it experiences danger. So the feelings of fear that come about in dangerous situations are in a sense no different from any other kind of conscious experience. The only difference is in the system that consciousness is paying attention to the danger processing system, the color processing system, the language processing system, and so on. So emotional feelings come about when we become consciously aware of the activity of an emotional system, which does its work for the most part outside of consciousness.
JB: What's the difference between an emotional and a cognitive memory?
LEDOUX: By cognitive memory I'm going to assume you mean explicit conscious memory, the kind of memory we usually have in mind when we use the word memory in everyday speech. Emotional memory and explicit memory happen at the same time, but separately. For example, the amygdala mediates emotional memory and the temporal lobe memory system mediates explicit memory.
Here's an example. Imagine driving down the road and having an accident. You hit your head on the steering wheel and the horn gets stuck on. You're bleeding and in pain. It's awful. Sometime later, you hear the sound of a horn. The sound goes to your amygdala and activates your autonomic nervous system (raising your blood pressure and heart rate, making you sweat), tenses your body muscles, releases stress hormones into your blood, and so on. The sound also goes to the temporal lobe system and reminds you of the accident, of who you were with and where you were going. It also reminds you that it was awful. But these are all just facts about the situation. They are memories of the emotional experience rather than emotional memories. In general, one difference between emotional and cognitive processing is that emotional processing often leads to bodily responses, whereas cognitive processing leads to more cognitive processing. Cognitions are seldom characterized by specific kinds of responses, but emotions usually are. It's important that we understand as much as we can about the biology of these systems.
Many people have problems with their emotional memories; psychologists' offices are filled with people who are basically trying to take care of and alter emotional memories, get rid of them, hold them in check. If anything, emotional memory is more basic than explicit conscious memory. For example, it takes place at an earlier age. It's conceivable, and in fact seems very likely, that a child could be abused very early in life and develop unconscious emotional memories through the amygdala prior to the point where the temporal lobe memory system has kicked in. If that's true then emotional memories are being formed for things that will never be consciously understood, because the system that mediates conscious memory isn't available to encode the experience and can therefore never retrieve it.
We need to understand how unconscious emotional memories are formed-- not only because they occur in early childhood, but because emotional memories are created throughout our lives. And it appears that these memories are indelible. They can be extinguished in the laboratory or treated in the psychiatrist's office, but they can usually be brought back. And recently we've been able to find a mechanism in the amygdala that might be responsible for this. It's sort of complicated, but the finding goes like this. We record neural activity in the amygdala before and after conditioning. Cells fire more to the tone afterwards. With extinction the firing rate goes back to baseline. However, in addition to measuring these stimulus-evoked responses, we measure the correlation in the time when different cells fire spontaneously (no stimulus present). After conditioning, some cells that were not correlated become correlated. And for some of the cells the correlations remain past extinction. In other words, the feared stimulus no longer elicits activity in the amygdala, but the amygdala cells continue to be functionally coupled. It's as if extinction (and therapy) doesn't erase the memory, it just weakens the ability of the stimulus to activate the memory. So in order for the stimulus to again be effective all you have to do is change the synaptic strength of the connection between the stimulus and the memory rather than recreate the memory.
This is relevant to phobia, where the phobia can be in remission (the sight of a snake no longer elicits paralyzing anxiety) and then the patient's mother dies and snakes regain their propensity for producing terror. Phobia is also a good way to illustrate the difference between cognitive memory of emotion and emotional memory. We aren't born with phobia. Somehow they are acquired through experience and stored in the brain as links between stimuli (like snakes or heights) and fear responses. Once a phobia is successfully treated (the snake no longer elicits overt fear responses) the patient still has the explicit memory of having had the snake phobia. In other words, the therapy inhibited the amygdala's pathological response to the sight of snakes, but the therapy didn't eliminate the temporal lobe memory system's memory of having had a snake phobia.
JB: How can you talk about unconscious emotional memories? Why is this different than inventing a concept like "repressed memories?"
LEDOUX: I'm not talking about memories that have been repressed, they're just not consciously available. I'll give you a simple example. Patients who have damage to the temporal lobe memory system are unable to remember what happened to them five minutes ago. If you take those patients and give them a sound, pair it with a shock, and you later give them the sound again, their autonomic nervous system responds, but they have no conscious memory of the experience that led to that. The memory is in the brain, having an effect on systems that we can measure, including autonomic and behavioral systems, but the patient has no conscious memory of it. In everyday usage, the term memory usually refers to conscious memory, but as scientists we use the term in a more general sense to mean changes in the nervous system that reflect past experiences. By this definition, we can see all sorts of memories that have no conscious counterpart. This is the idea of implicit, or procedural memories that are in the brain's systems, but not reflected in consciousness.
There's a famous case from the early days of this century that beautifully illustrates this point. The patient had a pretty severe amnesia. Each day she had to be reintroduced to her doctor, as she didn't recognize him. One day the doctor put a tack in his hand, and he walked in and shook her hand. When their hands met, her finger was pricked. He then walked out of the room, walked back in, and asked whether she'd ever seen him before. She said she hadn't. But when he stuck out his hand to shake her's, she held back. Although we don't really know what was going on in her brain, it seems likely that the implicit memory that the handshake was dangerous was burned into her amygdala, and that allowed her to protect herself from getting stuck again. She knew this implicitly--but she couldn't tell you why because she couldn't remember the experience that led to it. The amygdala was forming its memories, but the temporal lobe memory system was not.
Normally, these systems work in parallel to give rise to our conscious memories about emotional experiences, and unconscious emotional memories. In this sense, emotional memories are by definition unconscious. But they aren't unconscious because they've been repressed. They're unconscious because they are not formed by the conscious memory system. The conscious memory system forms memories about emotions, but doesn't form the emotional memories that have direct access to emotional response systems.