If a perceived threat feels far away, people tend to engage the more problem-solving areas of the brain. But if the threat feels urgent and up-close, animal instincts take over, allowing very little logical reasoning to occur, according to a new virtual reality (VR) study published in the Proceedings of the National Academy of Sciences.
This type of primitive reaction makes it harder to extinguish the fear of a close-up threat and more likely that you’ll have some long-term stress from the experience.
Research has shown that traumatic events that touch the body, like rape and other physical assaults, are more strongly linked to post-traumatic stress disorder (PTSD) than are traumas viewed at some distance.
Now, thanks to a clever adaptation that has placed study participants in a 3D virtual reality environment while their brains were being scanned by an MRI machine, researchers have seen just how the circuitry of those brain responses differ.
“Clinically, people who develop PTSD are more likely to have experienced threats that invaded their personal space, assaults or rapes or witnessing a crime at a close distance. They’re the people that tend to develop this long-lasting threat memory,” said senior author Dr. Kevin LaBar, a professor of psychology and neuroscience at Duke University.
“We’ve never been able to study that in the lab because you have a fixed distance to the computer screen,” LaBar said.
But Duke graduate student Leonard Faul and postdoc Daniel Stjepanovic, Ph.D, figured out a way to do it, using a 3D television, a mirror and some MRI-safe 3D glasses.
“It’s like an IMAX experience,” LaBar said. “The threatening characters popped out of the screen and would either invade your personal space as you’re navigating this virtual world, or they were farther away.”
For the study, 49 participants experienced a first-person VR simulation that had them moving down either a dark alley or a brighter, tree-lined street as they lay in the MRI tube having their brains scanned. Ambient sound and visual backgrounds were altered to provide some context for the threat versus safe memories.
On the first day of testing, volunteers received a mild shock when the “threat avatar” appeared, either two feet away or 10 feet away, but not when they saw the safe avatar at the same distances.
The findings show that near threats were more frightening and they engaged limbic and mid-brain “survival circuitry,” in a way that the farther threats did not.
The next day, participants faced the same scenarios again but only a few shocks were given initially to remind them of the threatening context. Once again, the subjects showed a greater behavioral response to near threats than to distant threats.
“On the second day, we got fear reinstatement, both near and far threats, but it was stronger for the near threat,” LaBar said.
Importantly, the nearby threats that engaged the survival circuits also proved harder to extinguish after they no longer produced shocks. The farther threats that engaged more higher-order thinking in the cortex were easier to extinguish. The near threats engaged the cerebellum, and the persistence of this signal predicted how much fear was reinstated the next day, LaBar said. “It’s the evolutionarily older cortex.”
Understanding the brain’s response to trauma at this level might point to new therapies for PTSD, LaBar said.
“We think that the cerebellum might be an interesting place to intervene,” he said. “Clinically, it’s a new interventional target. If you can somehow get rid of that persistent threat representation in the cerebellum, you might be less likely to reinstate (the fear) later on.”
Source: Duke University