While some students joke about their stress levels and the inevitable mental breakdowns that follow, UC Berkeley researchers have discovered that extreme stress can actually lead to serious mental illnesses.
By studying the hippocampus — the region in the brain that deals with learning and memory — the researchers were able to see that stress, which decreases the production of new neurons from stem cells found in this area, can negatively affect memory and lead to mental illnesses such as post-traumatic stress disorder or major depression. The research was led by Daniela Kaufer, a campus professor of integrative biology, and was assisted by graduate students Aaron Friedman and Sundari Chetty as well as researchers from UC Davis.
To conduct their study, Kaufer and her team induced “extreme levels” of stress in a group of rats by placing the rodents in a confined space where they could not move for periods of three hours a day, seven days at a time — a particularly traumatic experience when placed on a human scale.
“Seven days for a rat is like six months for a human,” Kaufer said. “But no physical pain was caused — just psychological pain.”
In addition to regulating learning and memory, the hippocampus in the adult brain generates stem cells, which can transform into neurons. But within the hippocampus of the rodents, researchers discovered a surplus of white matter cells of the brain instead of the normal number of newborn neurons.
An excess of white matter in the brain affects the way the brain is wired and alters emotional behavior. More alarmingly, these cell increases were consistent with the patterns seen in mental illnesses, Kaufer said.
“When there are chronic stressors leading to overstimulation of stress hormones, this can do damage at a biological level to people’s brains — and their coping responses,” said Stephen Hinshaw, a campus professor of psychology who did not participate in the research, in an email. “We see this most saliently in major depression.”
By injecting another group of rats with corticosterone — the rat equivalent of the human stress hormone cortisol — the stem cells in the hippocampus responded by producing more white matter than neurons.
Researchers, however, reported that a small amount of stress is good for the body. In an episode of three hours, acute moderate stress on the rats showed an increase of generated neurons.
Kaufer recommended some solutions for preventing escalating levels of stress, such as physical exercise — specifically, running.
The next step of the researchers will be to examine long-lasting changes in white matter caused by early-life stress and to determine whether these changes indicate a risk for the development of mental illness. They also plan to look at stress development in childhood and adolescence by exposing young animals to stress and studying their brains.