A study led by researchers from Berkeley and UCSF may help explain why some people are more resilient to traumatic stress than others and lead to possible therapies. Published in December in the journal Translational Psychiatry, the study found a link between increased myelination in the brain’s gray matter and post-traumatic stress disorder (PTSD).
Myelin, a whitish layer of fatty substances and protein, encompasses neuronal axons, much like insulation around electrical wire, speeding communication between distant areas of the brain. It is common in white matter, but less so in gray matter. Researchers speculate that increased myelination of gray matter could explain symptoms such as heightened fear response and hyperresponsiveness to traumatic memories.
This latest study bolsters earlier work by Berkeley biologist Daniela Kaufer. In 2014, Kaufer and her colleagues discovered that, in rats subjected to chronic stress, neural stem cells in the hippocampus, a part of the brain involved in memory, matured into myelin-producing cells called oligodendrocytes instead of neurons or supportive glial cells as normal. Intrigued by these results, UCSF psychiatrist Thomas Neylan contacted Kaufer to collaborate.
While Kaufer continued to work with rats, Neylan’s team concentrated on human subjects. Neylan and colleague Linda Chao, UCSF professor of radiology, conducted brain scans on 38 military veterans, half of whom were diagnosed with PTSD, half of whom were not. In the former, the MRIs showed increased myelination in the gray matter. Meanwhile, Kaufer’s team found similar results in adult rats.
In fact, specific components of the veterans’ PTSD symptom profiles correlated with regional changes in the brain. Subjects displaying place avoidance behavior, for example, showed increased myelination in the hippocampus, while those with cue-associated fear had increased myelination in the amygdala, a brain structure linked to emotion. Surprisingly, this kind of variation mirrored the findings in the rat data.
As Kaufer told Berkeley News, “We understand that there’s a lot of individual variation in humans, but with rats, they’re genetically identical, so you think when you expose them to stress you’re going to get the same response. But the response is extremely variable. They sort of fall into groups, such that some are really resilient, and some are vulnerable. And the ones that are vulnerable are vulnerable in different ways.”
The same holds for humans, said Neylan. “Some people are very avoidant. Some people are very hyperreactive. The idea is that if you can show that these different symptom clusters have different neural circuitry, it might actually lead us closer to subtyping people in a way that we could be more targeted in our treatment.”
