An old saying tells us not to dwell on an unpleasant event. A new clinical study suggests the saying has both psychological and neurological support for its validity. Along with his advisors, Thomas Ågren – a doctoral candidate in psychology at Uppsala University in Sweden – has shown that it is possible to erase newly formed emotional memories from the human brain.

There are two forms (at least) of memory, short-term and long-term. Short-term memory keeps a very small amount of information, about the seven digits of a telephone number, at your fingertips for a brief period – typically less than a minute. Long-term memory, on the other hand, seems to store nearly unlimited amounts of information for years or decades.

A long-term memory of an experience, however, is not formed immediately upon the fading of the experience from short-term memory. The information is slowly consolidated into long-term (potentially lifelong) storage over time. This is why some drugs or experiences (such as a concussion) are associated with a period of amnesia – their effects stop the consolidation process cold, so the memory is lost.

When we remember an experience, the memory of that experience briefly becomes unstable, then is restabilized by consolidation of the remembered event. In effect, we don't actually remember the original event, but rather a memory of a memory of a memory of the original event. By disrupting the reconsolidation process that follows re-remembering, we can change the content of memory.

Post-Traumatic Stress Disorder (PTSD) is a common result of combat situations (Photo: National Institute of Mental Health)

When a "fight, flight, or freeze" situation is recognized by the hippocampus, it sends a message alerting the amygdala for action. Such emotional responses are processed milliseconds before the rational and conscious brain realizes what is occurring. Whatever actions then ensue are initiated without conscious thought.

We also get no chance to process the connection between the situation and our reaction to it. This uncontrolled reaction is the force behind Pavlovian conditioning, in which a set of unremarkable conditions which is always followed by physical pain leads to fear of the initial conditions themselves.

In the Uppsala study, the researchers showed volunteers a picture with no emotional content, and simultaneously administered an electric shock. Following a small number of repetitions, the volunteers came to fear the picture alone.

Once fear of the picture itself had been established, the group of volunteers was split randomly into two experimental groups. Members of a first group were shown the picture, after which sufficient uneventful time passed to reconsolidate the memory connecting the picture with the fear.

Members of a second group, however, were shown the picture frequently enough that reconsolidation of the memory of the memory was continually restarted, and thereby blocked from completing. This actually rendered the memory connecting the picture with fear completely unstable, and destroyed the connection. At the same time, MRI scans showed that the activation by the memory of the amygdala vanished along with the fear.

The importance of this study is that many flavors of anxiety issues, such as phobias, post-traumatic stress, and panic attacks, are triggered by memories with unpleasant associations to which a fight, flight, or freeze reaction has become strongly connected. Indeed, the effect of disrupting memory consolidation is rather like phobic desensitization, in which a patient is gently introduced to the object of their phobia in small degrees. The difference is that disrupting memory consolidation attempts to prevent the phobia developing in the first place.

For example, a patient with a paralyzing fear of snakes might be presented with an image of a snake's tail peeking up through the grass of a neighbor's lawn as seen through a window from inside their own house. Prior to this, they would be taught behavioral techniques to reduce their physical reaction to this less threatening scenario. The goal is to create a connection between this image, which does contain a snake, and a far smaller fear reaction than they normally have to seeing a snake.

Bit by bit the image becomes more threatening – perhaps the snake is in the patient's yard, then the head is seen, then the snake is on the doorstep, and so on. In each case the same goal holds, to create a connection with less fear than before. By the time the patient is presented with a snake to handle, they react with the smaller amount of anxiety they have slowly learned to associate with the general subject of snakes.

Between the high stress level of simply living in modern society, the impact of news services detailing horrible crimes not from one's own locality but from around the world, and a large number of veteran policemen, firemen, and soldiers suffering from post-traumatic stress disorder, the toll of anxiety disorders has been climbing rapidly in recent years. Better treatments are needed, but so are preventative skills. The Uppsala study described herein suggests that both can be substantially improved from their current state of development.

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