SEP 06, 2015 01:59 PM PDT

Pathway to PTSD

Approximately 8 million Americans suffer from nightmares and flashbacks to a traumatic event. While this condition, post-traumatic stress disorder (PTSD), is particularly common among soldiers who have been in combat, it can also be triggered by physical attack or natural disaster.
This illustration shows a brain with the amygdala highlighted in the center. In the background are models of the serotonin molecule. 
Studies reveal that trauma victims are more likely to develop PTSD if they have previously experienced chronic stress. A new study from MIT  could explain why. The researchers found that animals who suffered from chronic stress before a traumatic experience engaged a distinctive brain pathway that encodes traumatic memories more strongly than in unstressed animals. Blocking this type of memory formation could lead to a new way to prevent PTSD, said Ki Goosens, the senior author of the study, which appears in the journal Biological Psychiatry and is reported in Drug Discovery & Development. The paper’s lead author is former MIT postdoc Michael Baratta.
As Goosens, an assistant professor of neuroscience and investigator in MIT’s McGovern Institute for Brain Research, explained, “The idea is not to make people amnesic but to reduce the impact of the trauma in the brain by making the traumatic memory more like a ‘normal,’ unintrusive memory.”
Goosens’ lab is trying to find out why chronic stress is so strongly linked with PTSD. “It’s a very potent risk factor, so it must have a profound change on the underlying biology of the brain,” she said.
The researchers concentrated on the amygdala, an almond-sized brain structure whose functions include encoding fearful memories, and determined that in animals that developed PTSD symptoms following chronic stress and a traumatic event, serotonin promotes the process of memory consolidation. By blocking amygdala cells’ interactions with serotonin after trauma, researchers kept the stressed animals from developing PTSD symptoms, but blocking serotonin in unstressed animals after trauma had no effect.
According to Baratta, “That was really surprising to us. It seems like stress is enabling a serotonergic memory consolidation process that is not present in an unstressed animal.”
Memory consolidation is what converts short-term memories into long-term memories and stores them in the brain. Some are consolidated more strongly than others. “Flashbulb” memories, formed in response to a highly emotional experience, are more vivid and easier to recall than typical memories.
The team further discovered that chronic stress causes cells in the amygdala to express many more 5-HT2C receptors, which bind to serotonin. When a traumatic experience takes place, the heightened sensitivity to serotonin causes the memory to be encoded more intensely, contributing to the strong flashbacks that often occur in patients with PTSD, according to Goosens.
Baratta explained, “It’s strengthening the consolidation process so the memory that’s generated from a traumatic or fearful event is stronger than it would be if you don’t have this serotonergic consolidation engaged.”
Memory consolidation can take hours to days, but once a memory is consolidated, it is very difficult to erase. However, it may be possible to either prevent traumatic memories from forming so strongly, or to weaken them after consolidation, using drugs that interfere with serotonin.
Goosens added, “The consolidation process gives us a window in which we can possibly intervene and prevent the development of PTSD. If you give a drug or intervention that can block fear memory consolidation, that’s a great way to think about treating PTSD. Such an intervention won’t cause people to forget the experience of the trauma, but they might not have the intrusive memory that is ultimately going to cause them to have nightmares or be afraid of things that are similar to the traumatic experience.”
About the Author
  • Ilene Schneider is the owner of Schneider the Writer, a firm that provides communications for health care, high technology and service enterprises. Her specialties include public relations, media relations, advertising, journalistic writing, editing, grant writing and corporate creativity consulting services. Prior to starting her own business in 1985, Ilene was editor of the Cleveland edition of TV Guide, associate editor of School Product News (Penton Publishing) and senior public relations representative at Beckman Instruments, Inc. She was profiled in a book, How to Open and Operate a Home-Based Writing Business and listed in Who's Who of American Women, Who's Who in Advertising and Who's Who in Media and Communications. She was the recipient of the Women in Communications, Inc. Clarion Award in advertising. A graduate of the University of Pennsylvania, Ilene and her family have lived in Irvine, California, since 1978.
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