One hundred and sixty years ago, Kierkegaard defined it as “the state of the human being, when he confronts his freedom,” and ever since philosophers, psychoanalysts, psychologists, and scientists have been trying to further explicate the sensation known as anxiety. This month, Richard Restak, a Washington based neuropsychiatrist and best-selling author of more than a dozen books on the brain, adds his contribution with “Poe’s Heart and the Mountain Climber: Exploring the Effect of Anxiety On Our Brain and Our Culture” (Harmony Books, 256 pages, $22). It’s an opportune time, as these days, the experience of anxiety seems more culturally pervasive than ever. His book is a synthesis of a number of different streams of thinking on the topic – from the literary to the neurological – that ultimately takes a pragmatic stance. “What’s demanded of us in the face of terrorism and other contemporary sources of anxiety,” Mr. Restak writes, “is a major realignment in our attitude toward anxiety itself.”

Q: What made you want to write about anxiety?

A: After September 11 anxiety became an everyday fact of life. We’d never had anything like it before. The closest thing was Pearl Harbor, which is not only far away in most people’s minds now, but at the time was at a distance psychologically and geographically. Now, because of the media – television, in particular – we find out about anything that’s anxiety-provoking that’s happening anywhere in the world in a matter of minutes. There we are: We’re right in the middle of whatever the latest anxiety-invoking agent is.

And yet writers of past eras have suggested that theirs is the Age of Anxiety. How is our era any more anxious?

The entire commercial part of our culture is built up around anxiety. The anxiety-free person doesn’t buy anything and doesn’t go out anywhere, because he’s perfectly self-contained. The person that’s so anxious that he can’t function doesn’t leave his apartment to buy anything either. Marketers therefore try to keep a constant, low level of anxiety.

What’s the difference between anxiety and fear?

Fear is focused, and short-lived. Anxiety is diffuse, and can persist over a much longer span of time. It’s an inner conflict, a feeling of vulnerability. Someone who is anxious worries about things that are uncontrollable, excessive, or unrealistic. For instance, you can be fearful of spiders, but if you’re constructing your whole world around trying to avoid spiders – having cleaning crews coming into your apartment all the time, say – that’s anxiety about spiders. It’s very common that people don’t make the distinction.

One of the main points you make about anxiety is that it isn’t all bad – that it is, in fact, a necessary aspect of human experience. What benefits come from the ability to feel anxiety?

It’s more a matter of what happens if you don’t have anxiety. Often people who don’t have any anxiety at all are either psychopaths or have some sort of serious problem with human relationships, because the ability to experience anxiety is linked up with the ability to experience many other positive human emotions. It’s really only when anxiety becomes disruptive, extensive, and overpowering that it’s a bad thing. Up until then it can stimulate you to achieve. Think, for instance, of a test you’re anxious about. If you’re so laid back that you’re not even thinking about it, you’re probably not going to do very well – you’re not going to study for it, you’re not going to prepare for it.

As a neuropsychiatrist, a large part of your book is written from the perspective of brain research. Do you think this approach has a benefit over previous models of anxiety?

I think it’s better to look at anxiety from the point of view of the brain than from the point of view of psychoanalysis or psychology. I’ve written 15 books on the brain, and one of the things I’ve become totally convinced of is that the more you understand about how your brain functions the better you’re going to do, because it allows you to externalize and objectify things which up until to that point have just been subjective. There’s a decided benefit to saying, “I’m really feeling anxious here, my amygdala must be overactive,” instead of, “I must be anxious because of poor toilet training.” The neurological approach is liberating instead of enslaving. It allows you to be in control.

Anxiety and depression used to be considered separate entities. What brought thinking about them closer together?

Mostly it was the finding that anxious people are frequently depressed, and that depressed people are frequently anxious. It makes sense. If you’re consumed with anxiety it can get pretty depressing after a while. To think every day you’re going to get up and that’s the way you’re going to see the world, you can easily slip into a depression. By the same token, if you’re depressed and you don’t feel any happiness, it’s liable to make you anxious and wonder, “Is this the way I’m going to feel for the rest of my life?” And the evidence goes beyond that. There is an indication that a good 15% to 20% of people who have generalized anxiety disorder have depression. In essence, there’s a continuum of depression and anxiety. It’s difficult to separate one from the other.

In the book you draw heavily on the distinction between “trait anxiety” and “state anxiety.” Could you explain the difference between these two categories?

Trait anxiety is the tendency to become anxious. Someone who has the anxiety trait, whatever comes up that’s stressful they’re going to get anxious and may well become dysfunctional. State anxiety is the experience of anxiety itself. So people with high levels of trait anxiety slip easily into state anxiety. They can be opposed to the type of people who don’t get very anxious – the kind of people you want operating on you if something goes wrong, or handling the airplane if there’s a problem. The message of trait anxiety is that there are genetic contributions to our anxiety level. We can change our tendency toward anxiety up to a point, but we can’t alter it completely. It’s just not the way the world works; it’s not the way the brain works.

Who’s the least anxious person you’ve ever met?

I do a lot of forensic work and so I meet a lot of criminals – people on death row. They’re pretty anxiety free. They’ve always been anxiety free. That’s why they never saw the likelihood they’d wind up where they are. That type of future didn’t arouse the kind of anxiety it would in you and me. That’s what I mean by there being a great disadvantage to not being able to experience anxiety.