A newly discovered brain circuit in mice helps relax the brain during times of extreme stress.
A lead researcher says the study results suggest similar processes may occur in the human brain.
The study may help scientists identify why stress is so debilitating for some, like those with ADHD.
Think about a time when you had to suddenly slam on the car brakes or got a long email from your boss first thing Monday morning.
That sense of panic or feeling of overwhelm eventually dissipates, at which point you begin to see the situation more clearly — the construction down the road that brought traffic to a stop or the list of tasks in your boss's email you can start tackling one by one.
In the past, focusing in a high-stress situation may have meant the difference between life or death — the ability to outsmart and escape a charging predator, for example.
But scientists haven't had a strong grasp on what triggers that key transition from panic to focus. They thought the brain just needed some time for the neurotransmitter called noradrenaline — basically adrenaline for the brain — to dissipate.
Then, a new study of stressed-out mouse brains revealed something entirely surprising: a never-before-seen brain circuit that channels noradrenaline to special brain cells called astrocytes.
While the mice were stressed, researchers saw the astrocytes kick into high gear, helping the animals' brains relax and regulate the flood of overexcited neurons that contribute to the "fight or flight" stress response.
Mouse brains are, of course, different from human brains. But human brains also contain astrocytes that may function in a similar way.
If the brain circuit is similar in humans, it could help scientists get a stronger grasp on attention disorders, including ADHD, and develop better treatments.
A new brain circuit
Researchers from the University of California San Francisco examined the brain activity of mice under acute stress and discovered that noradrenaline in the brain actually sends two messages — one to neurons to engage alertness and one to astrocytes to calm overactive neurons.
"I did not expect that astrocyte activity would so closely track changes in arousal state of the animal," said Kira Poskanzer, senior author of the study and an associate professor of biochemistry and biophysics.
Astrocytes are star-shaped cells located between the brain's neurons. Until recently, they've been relatively understudied because scientists regarded them as more of a support system instead of a star player.
But this new study demonstrates they play a pivotal role in activity between neurons.
"We can learn a lot about how the brain works when we focus on elements, like astrocytes, that have been left out of most traditional neuroscience research," Poskanzer said.
A better understanding of stress management and hyperactive disorders
People with hyperactivity disorders typically experience worsened symptoms under stress. It can be difficult for them to calm down and regain focus.
If scientists could pinpoint the mechanism that triggers our brains to relax and regain attention, focus, and perception during stressful times, then it's fair to say that this could open the possibility of learning to harness it to better help people who are severely affected by stress.
Because this was an animal study conducted on mice, researchers can't say for sure how the findings might translate to humans.
That said, both mice and humans are mammals, and the study "suggests that human astrocytes may also be important for regulating neuronal activity in the cortex," Poskanzer said.
And because the newly discovered brain circuit in mice helps control attention and perception, it could play an important role in treating attention disorders, and other neurological and psychological disorders, Poskanzer said.
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