The results of a new brain imaging study may have just answered a big question about how stress changes the brain. Using a combination of genetic editing and brain scanning in mice, researchers found that stress triggers a chemical cascade that radically changes how brain networks communicate, and the results could sharpen our understanding of anxiety disorders in humans.
Breaking down the research
Stress serves an important purpose in preparing us to react to danger. Anything the brain perceives as threatening triggers multiple brain networks to synchronize and communicate, all in just a fraction of a second. With systems humming, we make immediate decisions to survive the threat.
But what facilitates all of those brain networks to connect and communicate? That’s been a difficult question to answer in the human brain, because doing so would require examining brain function during the split-second window of facing a threat.
Enter our friends the mice to help solve the problem. Researchers followed a trail of previous studies and zeroed in on the neurotransmitter noradrenaline (aka norepinephrine, a chemical that floods the brain during stress) as a likely facilitator of brain-network connectivity. The twist was that they had genetically edited the rodents’ brains to allow for selectively controlling when noradrenaline was released (not possible in human brains). While controlling the chemical faucet, they also scanned the mouse brains using fMRI to see what would happen.
And what happened, it turns out, was pretty amazing. The release of noradrenaline “rewired” the mouse brains, allowing different brain networks to instantly cross-communicate. But the neurotransmitter wasn’t just facilitating communication, it was restructuring neural connections beyond anyone’s expectations.
“I couldn’t believe that we were seeing such strong effects,” said the study’s first author Valerio Zerbi, a brain imaging specialist from the University of Zurich.
The researchers found the strongest rewired effects in brain areas responsible for processing sensory stimuli (auditory and visual, for example), and in the amygdala, the epicenter of the brain’s threat response system.
What does this mean for us?
It’s the part about threat response that may hold the most promise for better understanding what stress does to our brains.
Allowing for the fact that this was research in mice, the particular dynamic studied here is probably quite similar between us and our rodent counterparts. If noradrenaline rewires the human brain as it appears to rewire the brains of mice, it’s possible the long-term effects of stress are more profound than we’ve realized.
Previous research has linked the flood of noradrenaline to changes in brain connectivity, but it seems likely we’ve underestimated the effects, especially in the small but powerful part of our brain sitting at the center of anxiety disorders: the amygdala.
At a minimum, this research opens new doors for better understanding how both acute and chronic stress effects the brain, and could enlighten new ways of deconstructing anxiety conditions, now the most prevalent mental health disorders worldwide.