How Chronic Stress Changes the Brain
It was already established that someone with post-traumatic stress disorder (PTSD) sometimes shows an imbalance between the amount of gray and white matter in the brain.
White matter refers to the white color of the myelin sheath surrounding its axons. This whitish sheath promotes the smooth flow of electrical signals between cells. It might help to think of white matter as the communication pathway.
Gray matter, where the brain stores information, is made up of neurons and glia. Although science has known that stress is linked to changes in the volumes of white or gray matter, it was not understood how those changes occurred.
A study from University of California Berkeley researchers focused on cells in the hippocampus region of the brain, which governs emotions and memory and is often implicated in the manifestation of mood disorders. Researchers examined stem cells from the hippocampus of adult rats under the assumption that these cells would develop into either glial cells or neurons, which make up gray matter.
When these stem cells were exposed to chronic stress they also developed into a type of glial cell that produced myelin sheath. These glial cells, known as oligodendrocytes, also promote axon pathways and synapses. Synapses and axon pathways have to do with cell communication which is the function of white matter.
Researchers say that fewer information holding neurons might explain why people with PTSD or other chronic stress conditions have trouble with memory and learning. This research offers greater insight into not only how it is that the imbalance of gray to white matter comes about, but also how that imbalance is manifested.
Integrative biology professor Daniela Kaufer, part of the Berkeley study, says that imbalanced communication, or connectivity, between various parts of the brain might be behind PTSD symptoms.
If emotional (hippocampus) and stress response areas (amygdala) of the brain experience strengthened communication, you would expect to see things like more pronounced startle responses and fight-or-flight responses – anything relating to fear. And that is precisely what one observes in a person suffering from PTSD. This response would be further amplified in the absence of strong communication between the hippocampus and the brain region responsible for modulating responses (the prefrontal cortex).
In other words, chronic stress affects how stem cells develop. Stress can cause stem cells that should mature into information-storing neurons to develop into information carrying cells instead. If emotion and fight or flight areas are working but the area which would calm fears are not working, then the person will have tremendous difficulty managing overreactions to perceived fears.
Kaufer and her team looked only at the hippocampus region of the brain. She believes that further investigation into other regions might reveal how changes in white matter could be affecting conditions such as depression, autism, schizophrenia, attention deficit hyperactivity disorder and even suicide.
Kaufer is currently studying how chronic stress in the first months of life affects white matter. She is also interested in whether or not such changes may be connected to vulnerabilities in later years.