Tuesday, August 27, 2013
The trail of trauma
When a disaster strikes, groups of people spontaneously form and start talking all at once.
And your brain does the same thing in response to personal trauma.
Groups of neurons in the cerebral cortex start firing at the same time, "talking" to each other, and get locked into a correlated pattern of activity.
Previous work by University of Minnesota researchers identified a particular pattern so strongly associated with post-traumatic stress disorder (PTSD) that they can clearly tell who has PTSD. Now, a new study shows that in people with PTSD, these patterns persist, just as do the intrusive, incapacitating memories or re-experiencing of the events, emotional numbing, and hyperarousal that define the disorder.
But, they found, in people who have not developed PTSD despite exposure to trauma, the patterns lack staying power.
In them, "these patterns loosen and dissipate over weeks, months, or days," says lead researcher Lisa James, an assistant professor in the U's Department of Psychiatry and a researcher in the Brain Sciences Center at the Minneapolis VA Medical Center, where the study took place. "This wipes the slate clean.
"Our work means that in resilient people the brain can actively adapt to traumatic experiences in a way that those with PTSD cannot. The better we understand the brain mechanisms associated with PTSD, the sooner we can apply that knowledge to evaluating treatment efficacy."
Co-author Apostolos Georgopoulos likens the situation in a trauma-exposed brain to an infection.
How MEG works
The advantage of MEG is its ability to detect brain activity on a scale of milliseconds. The researchers placed an apparatus resembling a helmet over the heads of the subjects, who were asked to fixate on a stationary dot with their eyes for 60 seconds. The helmet contained 248 sensors, each of which detected the magnetic fields generated in a population comprising tens of thousands of cortical cells. Together, the sensors scanned the magnetic activity over the whole cortex.
'It's like having a disease, where you make antibodies," says Georgopoulos, a Regents Professor of neuroscience and director of the Brain Sciences Center. "If you can't make antibodies, you don't adapt to the virus. Similarly, if you don't de-correlate your brain networks, you're still sick."
Short-term tracking of the PTSD-linked patterns in people exposed to trauma could potentially identify those who are resilient vs. those who need treatment. Pattern tracking could also be used to monitor progress during PTSD treatments or to validate a simpler test for resilience, such as genetic or personality traits, the researchers say.
The work is published online in the journal JAMA Psychiatry.
How to eavesdrop on brain chatter
The researchers studied 86 veterans with PTSD and 113 veterans who were resilient to trauma. A questionnaire revealed the extent of their exposure to trauma; those with trauma exposure but no PTSD were, by definition, resilient controls.
The team used a noninvasive technique called magnetoencephalography (MEG; see sidebar)) to study the magnetic fields generated in neurons of the right temporal lobe cortex as they received messages during neuronal "talk." Neurons receiving messages experience movements of ions across their outer membranes; these movements generate the magnetic fields.
The MEG measured the strength of correlated patterns of activity in cell populations—i.e., simultaneous generation of magnetic fields—characteristic of PTSD. They discovered:
- Among controls, weaker PTSD-related patterns tended to occur in those with higher trauma scores. In other words, "In controls, big trauma leads to a big adaptation," says Georgopoulos.
- Also in controls, the right temporal cortex had a crucial node in which brain activity was decorrelated, a signal of adaptation. This area of the brain is a focus of future study.
- Resilience isn't an all-or-nothing trait, but a continuum.
The trauma landscape
Most people are resilient to some events, so the question becomes: Why isn't everybody?
"About 60 to 90 percent of people will experience a potentially traumatic event in their lifetime, like a car accident or the sudden death of a loved one, but they are resilient. They don't develop symptoms of a psychiatric disorder," says James.
"Only seven percent of people in the general population and about 20 percent of veterans develop PTSD. Most come back [from service] without PTSD—what enables them to do that?"
To answer that question, the researchers are turning their attention to a search for genetic markers of resilience. If certain genes or, perhaps, personality traits, are found to be associated with resilience, that could allow researchers to predict one's degree of resilience before trauma hits.
"PTSD sufferers have options that include medications, talk therapy, and interventions to treat nightmares," James says. "We're interested in what happens in the brain as individuals with PTSD respond to treatment."
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