“Now what was I doing?” As anyone who has found themselves staring at the shelves in their supermarket or at their computer screen after having been lost in thought about some worrisome situation in their life knows, stress affects your brain.
New research from the University of California, Berkeley provides insight into what the impact of chronic stress on the brain actually is. The team found that chronic stress brings about permanent changes in the balance between the brain’s white matter and grey matter.
Stress is known to produce different physiological reactions, such as the "fight or flight response," as well as contribute to long-term psychiatric illnesses like depression and post-traumatic stress disorder (PTSD).
Stress disrupted the white matter/grey matter balance and could provide an explanation for the effects of stress on learning and memory in the brain.
White matter is made up of axon (nerve) fibers that conduct electrical signals throughout the brain. The axons are surrounded by a protective white fatty sheath known as myelin.
The brain’s grey matter consists of the brain cells that receive these signals and communicate with other brain cells in a particular region.
The scientists discovered that stress generates more myelin-producing cells — known as oligodendrocytes. The excess of myelin alters the delicate balance between white matter and grey matter and disrupts timing of communication within the brain.
In the study, the scientists exposed sets of lab rats to a series of behavioral tests that induced physical stress. When they looked at a region of the brain known as the hippocampus — an area crucial for memory and emotions — they observed more myelin cells and fewer regular brain cells.
The denser network of white matter could create permanent changes in brain connectivity. PTSD patients have stronger connectivity between the hippocampus and a region called the amygdala, which is the center of the brain’s “fight or flight” response. In contrast, PTSD patients exhibit lower connectivity between the hippocampus and prefrontal cortex, a brain region that moderates responses to stress.
The results from the study may also be evidence of a connection between stress and other brain disorders. According to Daniela Kaufer, senior author, “Our findings could provide insight into how white matter is changing in conditions such as schizophrenia, autism, depression, suicide, ADHD and PTSD.”
Stress caused a reprogramming of neural stem cells in the brain of adult rats, the study found. These special stem cells are not found in the embryo, like most stem cells, but persist into adulthood and can become new neurons in a process called neurogenesis.
While most neural stem cells in the hippocampus give rise to regular brain cells, or grey matter, the scientists discovered that after stress, these neural stem cells more often became oligodendrocytes, the myelin-producing cells of white matter. This disrupted the white matter/grey matter balance and could provide an explanation for the effects of stress on learning and memory in the brain.
The researchers are now investigating several anti-stress therapies, such as exercise and antidepressant drugs, to see whether they can fix the imbalance between white matter and grey matter. They also plan to look at the effects of stress on the white matter vs. grey matter imbalance in patients with PTSD.
The study is published online in the February issue of Molecular Psychiatry.
