A student with a photographic memory was once writing an exam, and realized that time was running out. Panicking, she “opened up” the textbook in her mind to look for answers, and later confessed that she had cheated.
Many of us can only wish to have such vivid recall. But what we remember may also be a curse: some people are often ambushed by memories of horrific events. Their life is a battle between the past and present, and their mind becomes imprisoned by past trauma.
These individuals suffer from post-traumatic stress disorder (PTSD), a chronic and debilitating condition in which memories of traumatic events are uncontrollable and crippling.
By using magnetic resonance imaging (MRI), a technique that takes snapshots of the brain at work, a study at the University of Western Ontario has shown that PTSD sufferers remember horrifying experiences mostly in the right hemisphere, which stores images and emotionally meaningful events. For those who have gone through trauma but developed no post-traumatic symptoms, the remembering occurs mostly in areas that process language, housed predominantly on the left side of the brain.
What this means is that when individuals with PTSD remember a life-threatening car accident or the sight of someone buried alive in an earthquake, it is a flashback as vivid as if they were re-living the event.
But for those who do not develop PTSD, a trauma is just another autobiographical memory that fades with the passage of time.
So why are some traumatized victims able to move on while others can’t? According to Dr. Martin Katzman, a professor of psychiatry at U of T who specializes in anxiety disorders, it could be due to a person’s innate sensitivity to stress. Alternatively, prior history of trauma also makes a person more vulnerable to developing post-traumatic symptoms.
In our brain, a structure called the amygdala coordinates our behaviour in situations that have emotional significance, such as those with signs of danger. Traumatic memories that have not been “digested” may be stored here, says Dr. Susan Bradley, also a psychiatry professor at U of T, specializing in affect regulation and the development of psychopathology.
When you have experienced something that is upsetting, you tend to go back and rehearse it until you understand why it happened and what you could do to prevent it in the future. Bradley says this process of “digestion” allows you to use your language-based mental capacity to make sense of the experience, and develop a certain level of control over it. Storing memory in the left half of the brain can do that for you.
On the other hand, memories that have not been “digested” could be easily triggered by things like smell and visual cues. The experience is instantly replayed, which is why traumatic memories are so intrusive for people with PTSD.
Prolonged stress is linked to structural changes in the brain. “There is some belief that it actually knocks out some cells in the part of your brain called the hippocampus, which is responsible for memory,” Bradley continues.
The hippocampus inhibits the activity of the amygdala. Katzman explains that chronic stress inhibits the production of a protein that stimulates brain cell regrowth. People in chronic stress have the dual disadvantage of losing hippocampal volume and not having enough of this protein to direct the reproduction of brain cells. Their hippocampus shrinks and cannot adequately inhibit the amygdala.
But there is some evidence that exercise and anti-depressants may contribute to brain cell reproduction and help turn things around. Once researchers have identified exactly how and where traumatic memories are stored, Bradley says there may even be the possibility of using new technology like trans-magnetic stimulation to stop them from being stabilized in PTSD patients.
“You could perhaps argue that PTSD is a disorder of hyper-arousal. [But] some people may argue that PTSD is a disorder of memory, because [patients] get stuck with one foot in the past and one foot in the present, but it’s more complicated than that,” Katzman says.
As pointed out by Dr. Klaus Kuch, a professor in the department of psychiatry at U of T with specialization in anxiety disorders, the experience of flashbacks is not only visual but also physiological. The person may sweat, feel nauseous, be mentally panicky, have an increased heart rate, and the list goes on.
PTSD is probably the most complicated illness to understand, Katzman continues, because, “you have a pretty normal person whose brain is damaged not by physical trauma-not by an injury to the head-but by an emotional one.”
