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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Minding Your Mind Minding Your Mind

Overcoming Scary Memories

November 13, 2013

By Michael Craig Miller M.D.

Harvard Medical School

The dramatic landing of U.S. Airways Flight 1549 in the Hudson River in early 2009, and the rescue of all 155 people aboard, was a testament to good flight training, as well as the calm and focused demeanor of the plane's pilot and crew during the crisis.

But in several interviews afterward, Capt. Chesley Sullenberger and his crew spoke of having flashbacks and trouble sleeping, and feeling distracted. These are typical reactions following a trauma.

When we experience a physical or psychological trauma, it is common to replay the events over and over in our thoughts. While many people eventually recover from the emotional aftereffects of trauma, others develop anxiety disorders. Psychotherapy can help patients become desensitized to fear-inducing memories, but it doesn’t work for everyone.

Research into how we form memories suggests two newer ways to help lessen the fear a memory can provoke. One approach combines drugs with psychotherapy techniques. The other tries to eliminate the frightening part of a memory.

Memories in Motion

Memories form in stages. At first an emotional memory is unstable, that is, it is just a pattern of electrical signals in the brain. An event that triggers a strong emotion strengthens nerve connections and reinforces these electrical signals. This "consolidates" the memory or makes it permanent — or so the thinking went, until recently.

Animal studies have shown that when we recall a frightening memory, it is reactivated. That is, it returns to a biologically unstable form, similar to when the memory was first formed. From this reactivated state, the memory then is reinforced through a process of reconsolidation.

Early studies with human subjects suggest that if this process is interrupted by, for example, a drug or a new experience (such as seeing a therapist), even a previously consolidated memory may weaken or disappear.

Enhancing Psychotherapy

Let's take a simple case of a person who is frightened by spiders and has a strong emotional reaction to seeing one. A psychotherapist may try an approach called exposure therapy. It helps the patient learn to respond differently to a fearful stimulus or memory.

Neuroscientists call this process fear extinction. They once thought it worked by blocking or "unlearning" an anxious response. But more recent research has shown that fear extinction actually involves the formation of a new memory rather than the loss an old one.

The difference is not just words. If fear extinction involves creating a new memory, then strengthening this new memory in some way might help ensure that it wins the competition against an older memory that causes fear.

Researchers have therefore been testing various drugs to see whether they can be combined with psychotherapy to better dampen the fear response. One is the antibiotic D-cycloserine. It boosts activity of glutamate, a brain chemical needed for learning and memory. The researchers hoped it would also boost the process of fear extinction.

  • In one double-blind, placebo-controlled study, 28 people who were afraid of heights were randomly assigned to take D-cycloserine or a placebo before undergoing two virtual reality sessions that exposed them to heights. A week later, participants who took D-cycloserine reported less fear, and had improved results on skin tests that measure the stress response than people who took the placebo pill. The results held up during a follow-up assessment three months later.
  • Another pilot study randomly assigned 27 people with social anxiety disorder to take either D-cycloserine or placebo. Subjects took the pills one hour before each of four therapy sessions designed to help them overcome a fear of public speaking. Immediately after therapy ended, as well as one month later, participants who took D-cycloserine reported feeling less anxious than those who took the placebo.
  • Two other pilot studies have concluded that D-cycloserine might also help patients with obsessive-compulsive disorder respond better to psychotherapy to help reduce obsessive behaviors and other symptoms.

Scrubbing Away the Fear

A different approach is to erase the fear-inducing part of a memory — or at least take away its emotional punch. According to neuroscientists, this strategy impairs reconsolidation. In order to work, however, therapy must be timed exactly to occur during or shortly after a stored memory is recalled, and before it becomes reconsolidated — a period of only a few hours.

Because stress hormones such as cortisol help to consolidate fear-inducing memories, researchers have most often tested beta blockers as a possible way to block or slow the reconsolidation process. (Beta blockers counter some of the effects of stress hormones.)

That's what a group of researchers in Amsterdam did. In their carefully done study, the beta blocker propranolol appeared to erase the emotional part of a scary memory. (See "The Two Types of Memories.")

Two Types of Memories
Declarative - Our memory for the facts, such as the spider's appearance (size or color) or its location (on the ground or in a web); it is consolidated in an area of the brain called the hippocampus.

Emotional -The feeling connected to the image of the spider; it is consolidated in an area of the brain called the amygdala.

Forty volunteers received a mild shock every time they saw a spider picture. This was the "fear acquisition" phase of the experiment. Not surprisingly, the volunteers soon learned to fear the spider — as indicated by their "startle" response — whenever they saw the spider again. As volunteers slept that night, their brains consolidated the memory of what they experienced.

The next day, 20 of the volunteers took propranolol, while the others received a placebo pill. All the volunteers then viewed the spider pictures again. This viewing "reactivated" the scary memories and the researchers measured the volunteers' startle responses. At this point in the experiment, both groups had similar startle reactions when seeing the spider pictures.

Once again, they slept. The theory was that the propranolol would jam receptors in the amygdala, thereby preventing reconsolidation of the fear aspect of the memory, but would not interfere with declarative memory reconsolidation in the hippocampus.

Finally, on the third day, the volunteers viewed the spider pictures again. Those who took propranolol the day before were significantly less startled when seeing the scary pictures than those who had received placebo. In some cases, the startle response was completely gone. And while volunteers who had taken propranolol remembered why they'd been afraid of the spider pictures (indicating their declarative memory remained intact), they were no longer scared (suggesting that the emotional memory was successfully altered).

But timing of drug therapy was everything. Another group of 20 volunteers underwent the same fear acquisition experiment, and then took propranolol on the second day without viewing the spider pictures again. (This means they did not reactivate the fearful memory.) On the third day, the volunteers looked at the pictures again. They were just as startled as they were during the fear acquisition phase. This suggested that a scary memory must indeed be recalled in some way, to return it to a state where it can learn another response, before propranolol can prevent its reconsolidation.

Future Directions

The effort to mold memories by using medications has the feel of science fiction. But the experiments are really not science fiction at all. They reflect our growing understanding of how the brain learns and remembers. In each case, the drugs alone were not the agent of change. They merely put the brain in a receptive learning state. It was ready to change in response to an experience.

These experiments also provide important examples of how experience changes the brain. When you recall a scary memory, the brain returns to a state where — with the right intervention — it can learn a different response. Thus, learning a more comfortable reaction to a scary image is not much different from learning from your piano teacher how to practice a tricky, frustrating or scary passage in a new piece of music.

Of course, coming to grips with an experience like surviving Flight 1549 is much more difficult than shedding an experimentally-induced spider phobia. Nonetheless, you can imagine how a therapist might use innovative fear extinction techniques to help you master scary memories as they crop up. If memories are less frightening, you should feel more resilient and better prepared to meet life's challenges.

Michael Craig Miller, M.D. is the former editor-in-chief of the Harvard Mental Health Letter and an assistant professor of psychiatry at Harvard Medical School. Dr. Miller has an active clinical practice and has been on staff at Beth Israel Deaconess Medical Center for more than 30 years.

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