If the memory doesn't fade
Traumatic experiences trigger fear in everyone. While most get over it over time, for some, the memory of the trauma continues to define their lives. Can you tell the difference between these groups by looking at certain brain structures? Even a puddle can trigger panic, fear and helplessness - when it reminds you of the water that suddenly came and took everything with it that wasn't nailed down and painfully burned into your memory. In most people, this response to otherwise harmless stimuli decreases over time and eventually disappears altogether. The connection between these stimuli and the trauma is then erased.
This deletion mechanism fails in some people: Even if they often cannot explain why, certain situations trigger anxiety attacks again and again. This special form of anxiety disorder is called post-traumatic stress disorder (PTSD). In addition to anxiety attacks, it brings nightmares, insomnia and memory loss as symptoms and makes it impossible for those affected to lead a normal life. To date, there is no promising therapy.
The disease has so far posed many mysteries to researchers. Above all, the question of why the association of neutral objects with the trauma – i.e. the puddle with a tsunami – wears off in some people, but is burned into the brain in others. To explore this, researchers at Harvard Medical School showed subjects without anxiety disorders images of rooms lit in either red or blue. One of the colors gave the subjects unpleasant electric shocks. They then saw all of the images again without any additional stimuli to erase the association of pain and color.
The next day, the researchers tested whether the erasure was successful, or whether the subjects still reacted with fear to the color associated with electric shocks. To do this, they used a familiar reaction of the body to fear or excitement: sweaty palms. The more afraid someone feels, the more their hands sweat. This increases the electrical conductivity of the skin, which can be measured using two electrodes on the palms of the hands.
In fact, there were differences between the subjects. Some reacted to images in both colors in the same way. Her brain seemed to have forgotten that one of the colors was associated with a painful stimulus, while others were noticeably more anxious. So the connection between color and pain was still stored in her brain.
To check whether the brain structures of the subjects who reacted differently differed from one another, the researchers compared images of the brains of the candidates from a magnetic resonance tomograph. The scientists suspected four brain regions, all of which are involved in the processing of fear stimuli, as a possible cause for a difference in the reaction. In fact, in one of these regions, just above the eye, they found a "the thicker the better" association.
The region, the ventromedial prefrontal cortex, is thought to be the link between memory and the brain's fear center, the amygdala. Only if they were comparatively thin did the subjects show unfounded fear on the second day of the experiment.
This result is not much further. To fully understand how the disease develops, people must first be studied before and after a traumatic experience. Achieving this will be very difficult. The plan is to study groups of people, such as firefighters or police officers, who are more likely to suffer trauma.
The results could also be of interest for the treatment of anxiety disorders. In order for a patient to lose his spider phobia, he is confronted with a harmless spider. Because it is harmless and nothing happens, the fear response gradually weakens until it eventually disappears. For some, however, such exposure therapy does not work - perhaps the reason for this is the brain's inability to unlearn fears. Perhaps in the future such patients can be spared an unsuitable – and unpleasant – therapy attempt by taking a look inside the brain.