Back in the 19th century, practitioners of phrenology traveled the country toting white, ceramic head models. Instead of hair on top, the bald mannequins sported a grid of lines and labels — like a “cuts of beef” chart for the brain. Scanning the head, phrenologists could easily see which parts of the brain were responsible for destructiveness, benevolence, wonder, or even weight.
Naturally, it all turned out to be bunk. But the idea that you can trace an abstract emotion or type of thought to activity in one specific corner of the brain is still very much with us. If you’ve read anything at all about neuroscience in the last few years, you’ve been introduced to chemicals that cause love, a hemisphere of the brain responsible for creativity, and the part of the brain that creates the sense of fear. Unlike phrenology, this isn’t bunk, but such pronouncements are oversimplified to the point that they mislead us about what’s actually going on in our heads.
Paul Whalen studies the amygdalae— two little lumps of grey matter, one in each hemisphere of the brain, that are frequently described as the places where our fears are born. Understanding the amygdala is definitely important to understanding fear responses, Whalen told me. But fear isn’t the only thing the amygdala does. In fact, as scientists have started to get a better idea of how the amygdala works that information has actually changed the way we think about fear, and anxiety disorders in particular.
I recently spoke with Whalen about why the amygdala gets labeled as the brain’s “fear center”, what it’s actually doing, and how this research could lead to new treatments for people with Post Traumatic Stress Disorder and other anxiety problems.
Psychologists who wanted to study emotion had to pick one, and fear is the easiest to study in a human or animal. It’s difficult to know how to make a rabbit happy. It’s easier to know how to make organisms afraid.
Maggie Koerth-Baker: Your research shows that the amygdala does a lot more than just make us afraid. In fact, your research suggests that the idea of “fear” involves a lot more than just reacting to something scary. But where did these ideas come from, to begin with? Why do we think of the amygdala as a “fear center”?
Paul Whalen: In the early 1980s, the psychologists who wanted to study emotion had to pick one, and fear is the easiest to study in a human or animal. It’s difficult to know how to make a rabbit happy. It’s easier to know how to make organisms afraid. People were doing Pavlovian fear conditioning. You have a tone that tells the animal it’s about to receive a mild shock. Then you can study all the brain areas that react to that. You immediately realize that you have a model for how and why we get anxious and how we begin to predict what will happen to us next. And the amygdala ended up being one of those brain areas.
That’s why we started with fear. Now, the big push is to study happiness, but what we mean is reward systems, there, as well — the processes that predict good outcomes.
You can end up being reductionist about what an emotion is. And that leads to misleading ideas about what part of the brain does what. Nobody understands better than we do that this is a naive heuristic. We’re not really talking about the feeling of fear or what you mean when you say you’re feeling afraid. But that’s a very difficult thing to study systematically. We're not actually trying to understand emotions, we're trying to understand the basis of a neural system.
MKB: Is it reasonable to link the amygdala and fear, then? I mean, is any part of the brain really a single-function tool … like a pie-crust crimper you’d buy from Williams Sonoma? Or are they more like, say, a food processor, able to do multiple jobs?
PW: There’s two answers to that. The first is that you have to start somewhere. Nobody believes that fear is the amygdala’s sole function and we know it can’t teach you everything you need to know about being afraid. But we do know it’s an older area of the brain and it’s reactive. It’s picked up on these things like facial expressions and it tells the brain, “the last time we saw that facial expression something bad happened.” It sends that signal to the prefrontal cortex, where decisions get made. The amygdala produces an alarm reaction and the prefrontal cortex is in charge of cancelling or corroborating the alarm.
Say you’re looking at a snake. That shape could mean danger. But it might not. The amygdala sends the same alarm despite the context, whether you’re in a field or in a zoo. The prefrontal cortex can cancel the alarm call in a zoo. [If the communication between the two parts of your brain is happening and the prefrontal cortex is working properly] the same stimulus should give very different outcomes based on context. We believe that circuitry is critical to how well people regulate anxiety and whether they will succumb to an anxiety disorder.
MKB: But what the amygdala does isn’t just about fear and anxiety, right? That seems to be what your research is showing.
PW: That’s the other answer. As you do more research, the next thing you realize is that the amygdala doesn’t just do anxiety. It’s not the fear center of the brain. Instead, it responds to things, and calls up other areas of the brain to pay attention to them. It makes the rest of the brain better at learning.
S.M is a patient whose amygdalae don't work. She can be afraid. But she’s bad at learning about the things that cause fear.
MKB: So, the amygdala is actually about how we pay attention to anything — not just stuff that makes us anxious or afraid — but anything?
PW: At the end of the day, it’s an attentional area of the brain. It tells us to be more vigilant, to be more aware of our surroundings right now. With that signal from the amygdala, your visual system or auditory system might see something or hear something that it would have missed otherwise. The amygdala sends the initial signal that tells the other parts of the brain to be better at what they do.
Here’s a human example. S.M. is a patient with bilateral amygdala lesions. She can be afraid. But she’s bad at learning about the things that cause fear. We show people these very exaggerated pictures of faces, some fearful, some not, and people give us a number for how afraid they should be. S.M, she’ll say something is a “2” on faces that other people say is a “5”. If I were to show you a fearful face, you’d look straight at the eyes. That’s where we get a lot of our information. But S.M. doesn’t. She stays focused on the middle of the face, or even goes to the mouth and chin. Her attention doesn’t go to the place where she should know you learn best. Now, if you tell her to look at the eyes, her ratings are normal. The amygdala wasn’t her source of the ability to be afraid. It was the source of her ability to know where to look to learn whether she should be afraid. The amygdala just facilitates that. It makes you better at learning what signals to pay attention to.
MKB: Does paying attention come first, or does the amygdala kick in and make you pay attention?
PW: It’s always monitoring on idle. It’s never off, the engine is always warm. It’s very automatic. We’ve used studies with backward masking — we’ll show people fear faces, but really quickly and cover them with a neutral expression face. People report only seeing the neutral face. But their amygdala still activates because of the fear face. So you’re not even consciously always privy to what the amygdala is privy to. It snaps to that attention without your permission. It can automatically react to something that you don’t necessarily “see” in the environment — the look of someone’s eyes, the shape of a snake — and once it goes, the vigilance level across your brain just changes. You might not even be aware of why that is, but now you start searching the environment much more carefully. This can be part of how you end up with panic attacks. But it’s also that healthy sense of wariness that we all have and should have. But the amygdala isn’t the voice in your head asking, “Is everything okay?” It’s the system that gets the voice going.
MKB: How does knowing this help us better understand what’s happening the brains of individual people?
PW: One front to our current research is watching differences in normal levels of anxiety, looking for translation to disorders. Part of what interests me in studying undergrads is that we’re hoping to pick up on something that will help people understand normal fluctuations and disorders. The idea is that people with anxiety disorders don’t recruit the prefrontal cortex as well as they should, and the degree to which they can recruit it predicts their symptom severity. So if you can recruit the prefrontal cortex a little, you’ll have fewer symptoms of PTSD than someone who can’t. We know there are problems with this system [the connections between the amygdala and the prefrontal cortex] in kids raised in neglectful situations. Those kids search for threats too often. We know hypervigilance is a key symptom of anxiety. The problem with anxiet disorders isn’t hyper fear. It’s hypervigilance.
Published 6:51 am Mon, Aug 12, 2013
amygdala, brain, emotion, fear, neuroscience, paul whelan, Science