A common blood-pressure drug can selectively dampen fearful memories, according to research published today in Nature Neuroscience.

The findings add support for a new approach to treating anxiety disorders: chemically blocking the emotional component of a memory as it is being recalled. In healthy volunteers, the drug was more effective than exposure therapy, one of the most common treatments for anxiety disorders, which involves repeatedly exposing patients to what they fear.

The research builds on preliminary tests in patients with post-traumatic stress disorder (PTSD), in which people who have experienced severe trauma, such as rape, are plagued by disturbing and uncontrollable memories of the event. "Anytime you can reduce the emotional component of a memory while leaving the other content intact is very exciting," says Seth Norrholm, a neuroscientist at Emory University, in Atlanta, who was not involved in the research. "We want patients to understand what triggers their fear without feeling the anxiety."

The findings also build on our understanding of memory, supporting the notion that even an old memory, once recalled, becomes labile and susceptible to alteration.

To create a memory, the brain moves information from short-term storage into long-term storage--a process called consolidation. Repeating a phone number soon after hearing it, for instance, uses short-term memory. But short-term memories are particularly vulnerable to interference; learning a second phone number shortly after the first is likely to wipe out the memory of the original number.

In recent years, scientists have discovered that the simple act of remembering a past experience requires that the memory be consolidated once again. And both animal research and some human studies have shown that during reconsolidation, long-term memories-- once thought to be fairly stable--can be more easily meddled with.

In the new experiment, researchers from the University of Amsterdam repeatedly showed healthy volunteers pictures of spiders, one image of which was followed by an electrical shock. As the person learned to link the spider with the shock, just seeing that picture triggered anxiety. Psychologist Merel Kindt and her colleagues assessed the emotional aspect of the memory by measuring how startled a volunteer was by a loud sound accompanying the picture. This "startle response" is linked to the emotional intensity of a memory and can be measured using the movement of the eye muscles as the volunteer blinks in surprise.

The next day, scientists tested the emotional association between the electric shock and the spider by measuring the volunteers' startle response after seeing the spider. During the tests, the researchers gave half of the group propranolol, a beta blocker that's been used for decades to control blood pressure, and the other half a placebo. On the third day, both groups remembered the link between the shock and the spider equally well: they both accurately reported when they expected to get a shock. But those who had been treated with the drug were less startled by sound accompanying the spider, suggesting that the emotional aspect of the memory had been dampened while the informational content was left intact.