In addition, it is estimated that nearly 15 percent of US soldiers returning from Iraq and Afghanistan develop Post-Traumatic Stress Disorder (PTSD).
PTSD can lead to myriad problems that hinder daily life – or ruin it altogether – such as drug abuse, alcoholism, marital problems, unemployment and suicide.
This increases the urgency to develop better treatment strategies for Anxiety Disorders.
Important new research has found that there is a type of cell in the brain that counteracts the fear response central to Anxiety Disorders, potentially paving the way for more effective drug treatments.
Brain imaging shows the amygdala is the center of the fear response
Brain imaging studies have revealed that the amygdala, a small structure in the brain known to play a key role in fear and Anxiety, is hyperactive in many of the Anxiety Disorders, including PTSD. It is also responsible for the formation of new fear memories as a result of experience, such as learning to fear the sound of a rattlesnake’s tail rattling.
A recent study by Denis Paré, professor at Rutgers University, has identified a critical component of the amygdala’s neural network, what are called Intercalcated Amygdala Neurons (ITC). These are normally involved in the extinction, or elimination, of fear memories. His research was published online by Nature on July 9, 2008 and is scheduled to appear in the print edition later in July.
The conditioned response
In order to understand the importance of this research, you must first understand conditioned response and the extinction process.
A conditioned response is something learned by humans and animals in response to events in their environment. The classic example of this is Pavlov’s dogs. He taught them to salivate when a bell sounded, whether or not there was food for them.
Humans learn to fear things based on events in their environment. If something happens to us, we associate the context of the environment at that time with the fear. This is conditioned response.
For example, we had a neighbor once who had grown up in Germany during WWII. As a girl she had seen the devastation that the bombs caused and knew people who had been killed or injured by them. She told us that the sound of air raid sirens struck such fear in her heart that she was almost unable to run to the air raid shelter. She learned a conditioned response to the sound of sirens.
The extinction of fear
However, a conditioned response can be diminished with the repetition of the things associated with the fear, but without the thing that caused the fear itself. This is the process called extinction. This process is similar to that used to treat phobias, where the person is presented with the feared object or situation in the absence of danger.
Returning to the example of our neighbor, she was first afraid of any siren. She gradually learned to not be afraid of fire trucks and police cars. Her fear was nullified by extinction.
Behavioral studies have shown that extinction does not completely abolish the initial fear memory, but rather leads to the formation of a new memory that inhibits conditioned fear responses. In other words, the new extinction memory counteracts the old fear memory.
But extinction memories are also context-sensitive, so they have to be relearned in every new situation where the fear response might be triggered.
Our neighbor had to learn how to not be afraid of sirens while riding in a car, while walking down the street, while in a building like her house, and so on. But she never lost her fear of weather sirens because they were so infrequently heard she didn’t learn new extinction memories for them.
Extinction memory will only be expressed if tested in the same environment where the extinction training occurred, implying that extinction does not erase the initial fear memory but only suppresses it in a context-specific manner.
What all this means and why it is so important
This study found that there are two mechanisms at work in the brain: the amygdala that remembers and produces fear, and the ITC neurons that play a key role in the extinction of fear. When the ITC cells were inhibited in their experiments, the researchers found that the extinction of fears was impeded, mimicking the behavior seen in PTSD.
The importance of this finding suggests that PTSD and other Anxiety Disorders reflect a deficit in the ITC cells that counteract memories of fear, and that the amygdala, which produces those fears, is hyperactive.
As a result, it might be possible to compensate for this abnormality by developing drugs that enhance the action of the ITC cells to counteract the fear produced by the amygdala.
What do you think?
The discussion of this new finding has been long and technical, and if you’ve gotten this far, I hope you grasp how important it is. For the first time, the possibility of extinguishing the fears of Anxiety Disorder has been found.
- Do you think this discovery is as important as I think it is?
- Did you mind wading through all the technical details to learn its importance?
As always, your comments are welcome!
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Resources used in this post:
National Institute of Mental Health. (2008, June 26). The Numbers Count: Mental Disorders in America. Retrieved June 30, 2008 from National Institute of Mental Health Web site: http://www.nimh.nih.gov/health/publications/the-numbers-count-mental-disorders-in-america.shtml
Paré, Denis; Likhtik, Ekaterina; Popa, Daniela; Apergis-Schoute, John; Fidacaro, George A. (2008, July 9). Amygdala intercalated neurons are required for expression of fear extinction. Retrieved July 22, 2008 from Nature Web site: http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature07167.html
Science Daily. (2008, July 11). Brain Cells Related To Fear Identified, Paving The Way For More Effective Treatment Of Post-Traumatic Stress And Other Anxiety Disorders. Retrieved July 18, 2008 from Science Daily Web site: http://www.sciencedaily.com/releases/2008/07/080710173007.htm
Xie, Yun. (2008, July 21). The fear switch. Retrieved July 28, 2008 from Ars Technica Web site: http://arstechnica.com/journals/science.ars/2008/07/21/understanding-the-fear-switch