Individuals respond with physical and emotional distress to situations that recall traumatic memories. Such responses usually diminish gradually, as those situations are repeated without unpleasant occurrences; this is called “extinction memory.” But some people continue to respond fearfully and develop post-traumatic stress disorder (PTSD).
Studies in animals have suggested that the ventromedial prefrontal cortex (vmPFC) – an area of the brain – may be involved in extinction memory.
Over two days, study participants viewed a series of photos of two rooms. Each room contained a blue or red light. On day one, participants viewed the photos several times, and then viewed them again with a mild electric shock delivered to their hands right after a blue light appeared. They then viewed a series of the photos with no shocks administered.
On day two, measurements of skin conductance were taken while the volunteers viewed the photos with both colors of lights displayed but no shocks given. The volunteers then had structural magnetic resonance (MR) images taken of their brains.
The MR studies showed that those participants who demonstrated less anxiety response to the blue lights the second day also had a thicker vmPFC. “That was the only area of the brain that correlated with extinction memory,” says Mohammed Milad, Ph.D., a research fellow in the MGH Department of Psychiatry and the study’s lead author.