If two people experience the same traumatic situation, like an armed bank robbery, for example, they will both likely have an acute fear response: increased heart rate, chills, hot flashes, nausea, abdominal stress, shortness of breath, chest discomfort, sweating and light headedness.
One may go on to recover from the trauma quickly. But the other may continue to re-experience this same fear response, developing a severe anxiety disorder known as PTSD (post traumatic stress disorder.
“Why, given the same trauma, do some people, within days or weeks, recover and they’re fine — but other people never recover. They sensitize, get worse and worse and worse, and their whole life is changed because of these indelible memories that haunt them?” asked Kerry Ressler, M.D., Ph.D., associate professor of Psychiatry and Behavioral Sciences at Emory University, at his recent Flexner Discovery Lecture.
Genes and environment establish a preexisting sensitivity to fear-based disorders, he noted. But the neural circuitry that underlies the fear response has been widely studied and is well understood, which offers hope for treatments that help alleviate such excessive fear responses.
“If we look at post traumatic stress disorder, it’s among the only disorders in psychiatry in which we know the causative factor, or at least the principal causative factor, which is the trauma,” he said.
In other cases, the trauma may not be as clear or well defined — but the underlying neurobiology of fear is the same. Fear responses are encoded “preconscious, primitive system centered on the amygdala, and it happens faster than one’s ability to be aware of it,” he said.
PTSD can be thought of as a disorder of learning and memory, Ressler said.
“When we think of learning and memory disorders, we think of the dementias, or the inability to form memories. Whereas disorders like PTSD are disorders in which the memories are too strong, the emotional encoding of those memories is too strong and cannot be inhibited.”
In his talk, Ressler, who is also a Howard Hughes Medical Institute investigator, detailed recent research on compounds that can interfere with these processes in animal models — and may represent novel interventions for fear disorders like PTSD, phobias and panic disorders, in effect helping trauma survivors “unlearn” the fear response.
Ressler also discussed his group’s work in identifying genes involved in PTSD among trauma survivors in an inner city population – a population in which PTSD rates are higher than in war veterans. This work identified a gene called PACAP – one of the first genes associated with learning and memory in fruit flies.
Ressler’s lecture was sponsored by the Vanderbilt Medical Scientist Training Program.
For a complete schedule of the Flexner Discovery Lecture series and archived video of previous lectures, go to www.mc.vanderbilt.edu/discoveryseries.
