How the brain responds to amazing events

Summary: Surprising events trigger the release of norepinephrine in the brain, which helps to focus and learn from experience.

A source: MIT

According to a new study by MIT, one way to do this is to release noradrenaline when your brain needs to focus on something important.

Produced by a device called the locus coeruleus in the depths of the brain, this neuromodulator has a wide range of effects on the brain. In a study of mice, the MIT team found that one of the key roles of norepinephrine, as well as norepinephrine, is to help the brain learn amazing results.

“This study shows that the locus coeruleus encodes unexpected events, and that attention to those strange events is critical for the brain to take into account its environment,” said Mriganka Sur, a Newton professor of neurobiology at MIT’s Department of Brain and Cognition. Science, a member of MIT’s Picover Institute of Learning and Memory, and the director of the Simons Community Brain Center.

In addition to their surprising role, researchers have found that norepinephrine can help stimulate reward-leading behavior, especially when it is unclear whether an award will be offered.

Sur is the senior author of a new study that emerged today nature. Vincent Breton-Provancher, a former MIT postdoctoral fellow, is now an assistant at Laval University and Gabriel Drummond, an MIT graduate student, is the paper’s lead author.

Modulating behavior

Norepinephrine, along with dopamine, serotonin, and acetylcholine, is one of several neurotransmitters that affect the brain. Unlike cell-to-cell neurotransmitters, neuromodulators are released through large parts of the brain, allowing them to have a more general effect.

“Neuromodulators are thought to perfuse large areas of the brain, thereby altering the stimulus or inhibitory disk that neurons receive from point to point.” “This shows that they need to have general brain functions that are important for their survival and for regulating the state of the brain.”

Although researchers have learned much about the role of dopamine in motivation and reward, less is known about other neurotransmitters, including norepinephrine. It is associated with increased arousal and alertness, but excess norepinephrine can lead to anxiety.

Previous research on the locus coeruleus, the brain’s main source of norepinephrine, has shown that it receives information from many parts of the brain and also transmits signals far and wide. In the new study, the MIT team began to study learning through a specific type of learning, or trial and error, called role-strengthening learning.

For this study, the researchers trained mice to push the lever when they heard a high-frequency tone, but not when they heard a low-frequency tone. When the mice responded correctly to the high-frequency tone, they received water, but when they pushed the lever when they heard the low-frequency tone, they received unpleasant air.

Mice have also learned to push the lever harder when the tones get louder. When the volume was low, they were skeptical about whether or not to push. Researchers have suggested that blocking the activity of the locus coeruleus, which prevents mice from pushing the lever when they hear low noises, may help them to take advantage of the noradrenaline gain in uncertain situations.

“The reward comes because it wants the reward because the animal is being pushed and the locus coeruleus gives critical signals to say‘ push now ’,” says Sur.

Researchers also suggest that the neurons that produce this norepinephrine signal send most of their production to the motor cortex, suggesting more evidence that this signal stimulates animals to act.

Surprise alarm

Although the first burst of norepinephrine stimulated the mice to take action, the researchers found that the second burst would be more frequent after the end of the test. When the mice won the expected prize, these explosions were few.

However, when the outcome of the trial was unexpected, the explosions were much larger. For example, when the mouse took a breath instead of the expected reward, the locus coeruleus felt a large burst of norepinephrine.

Most of the norepinephrine in the brain is produced by two locus-coercive nuclei, one in the cerebral hemisphere. Locus coeruleus neurons are marked with a green fluorescent protein. Credit: Gabi Drummond

In subsequent tests, the mouse would be less likely to push the lever when it was uncertain whether it would receive a reward. “Animals are constantly adjusting their behavior,” says Sur. “Even though he has already learned the task, he is adjusting his behavior based on what he just did.”

The mice also showed noradrenaline bursts in tests when they received an unexpected reward. These eruptions distributed norepinephrine to many parts of the brain, including the prefrontal cortex, where planning and other highly cognitive functions take place.

“The surprise-coding function of the locus coeruleus seems to be much more common in the brain, and this may be reasonable because everything we do is suddenly controlled,” says Sur.

Researchers are now planning to study the possible synergies between norepinephrine and other neuromodulators, especially dopamine, which will meet even more unexpected rewards. They also hope that the prefrontal cortex will help animals improve their performance in future tests to learn more about how to store short-term memory introduced by the locus coeruleus.

See also

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Funding: The study was funded in part by the Quebec Research Foundation, the Council for Natural Sciences and Engineering Research of Canada, the NARSAD Young Researcher Award from the Brain and Behavior Research Foundation, the National Institutes of Health, and the Simons Foundation Autism Research Initiative. Social Brain Center, China National Foundation for Natural Sciences and NIH BRAIN Initiative.

News about neuroscience research

Author: Anne Trafton
A source: MIT
The connection: Anne Trafton – MIT
Photo: Photo by Gabi Drummond

Original study: Closed access.
Mriganka Sur et al “Spatiotemporal Dynamics of Norepinephrine during Learned Behavior”. nature


Spatial-temporal dynamics of norepinephrine during learned behavior

Norepinephrine released by the locus coeruleus (LC) is a ubiquitous neuromodulator that is involved in several functions, including arousal, movement, and sensory gain and learning.

It is unknown whether the activation of norepinephrine-expressing neurons by LC (LC-NA) causes different components of specific behavior.

Here we show that the LC-NA action demonstrates precise time dynamics for activating two functions during the learned behavior: spa easy task performance and enhanced coding to increase execution accuracy. To test these functions, we used a mouse behavioral task to identify classroom listening stimuli and complete the task.

Optogenetic inactivation of LC showed that LC-NA activity contributed to both task performance and optimization. Imaging, target recording of LC-NA neurons using two-photon micro-endoscopy and two-photon output monitoring showed that transient LC-NA activation occurred before and after reinforcement.

These two components of phase activity were heterogeneously reflected in the LC-NA cortical results, so that the behavioral response signal was higher in the motor cortex and facilitated the task, while the negative amplification signal was more common among the cortical areas and improved response sensitivity. the next trial.

Thus, the modular targeting of LC results allows the implementation of various functions, in which some norepinephrine signals are distributed among the targets, while others are widely distributed.

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