Biology of fear

Until her 40s, Carol Brown’s life was plagued by frequent panic attacks -- an experience familiar to some 2.4 million Americans.

The first such attack occurred when she was 16 years old and riding in an elevator. Suddenly, said Brown, “my heart started racing, my hands were sweating, my breathing was shallow. I thought I was going to die. I didn’t tell anybody. I thought I was losing my mind.”

In a panic attack, a person feels a rush of fear or distress with no sense of its cause. This is often accompanied by heart palpitations, shortness of breath, numbness or tingling, lightheadedness, flushes, chills, nausea, sweating, trembling or shaking.

Many people rush to the hospital emergency room, fearful they are having a heart attack.

The first attack often makes people so afraid of another that they avoid anything associated with it. Women have more panic attacks than men.

For Brown, 54, of Belmont, Mass., that meant avoiding elevators. Later, after suffering panic attacks on the highway and in a supermarket, she avoided those places.

Years ago, doctors would likely have attributed panic attacks like Brown’s to some deep psychological problem. While that diagnosis still persists, they are now more likely to suspect biology.

“The biological hypotheses for panic disorders are based on several observations,” said Dr. Srini Pillay, director of the panic disorders research program at McLean Hospital in Belmont.

“Pharmacologic medications can stop panic attacks and panic attacks can be induced by various compounds,” he said. Panic attacks also occur “out of the blue, suggesting some sudden alteration in chemistry.”

They can also occur when a person is not anxious, and even occur during sleep, suggesting panic attacks may be tied to biological rhythms, he said.

Family history plays a role too, he noted. If you have a parent or sibling with panic attacks, you have four to eight times the normal risk of getting them as well.

In laboratory experiments, researchers have shown that panic attacks can be induced by sodium lactate or carbon dioxide, which change the acid-base balance in the brain, triggering shortness of breath, one of the hallmarks of panic attacks.

And panic attacks respond extremely well to medications such as Paxil, a type of antidepressant known as a selective serotonin reuptake inhibitor, or SSRI, which boosts the efficacy of serotonin.

Indeed, while SSRIs are about 60% effective against depression, they are effective 80% to 90% of the time in panic disorder, said Dr. Alexander Neumeister, an associate professor at Yale University School of Medicine.

Panic attacks also seem to occur in people who have overly sensitive “suffocation alarm” systems that cause the brain to perceive a shortage of oxygen when there is none.

These alarm signals, generated in the brain and in special receptors called carotid bodies in the large arteries in the neck, have a “periodic tendency to get fired off too easily and to misinterpret ordinary fluctuations as signals of suffocation,” said Dr. Donald Klein, a professor of psychiatry at Columbia University Medical Center who coined the term “panic attack” more than 40 years ago.

Scientists are closing in on the brain regions that may be involved in panic attacks. In a study published earlier this year, researchers showed for the first time, using PET scanning technology, that people who get panic attacks have one-third fewer of a certain kind of serotonin receptor in their brains. Serotonin is a key regulator of mood.

The good news is that, terrifying as they are, panic attacks are not in themselves harmful and rarely last more than a few minutes, although they can lead to dysfunctional behavior such as drinking, avoiding normal life activities and unnecessary visits to the emergency room.

“Anywhere from 60% to 80% of people with panic attacks are vastly improved by cognitive behavioral therapy or medications or both,” said Dr. Chris Hayward, an associate professor of behavioral sciences and psychiatry at Stanford University School of Medicine.

But perhaps the best strategy is to combine medication and behavioral therapy, said Dr. Joe Bienvenu, a psychiatrist at Johns Hopkins School of Medicine. Even after panic attacks are controlled by drugs, people often “have not learned that they will not have more,” he said. “This really requires going there and dealing with this anticipatory fear.”