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How the brain responds to sudden events – ScienceDaily – Verve Times

When your brain needs to pay attention to something important, one way it can do that is by sending a boost of noradrenaline, according to a new study from MIT.

This neuromodulator, generated by a structure deep in the brain called the blue locus, can have widespread effects throughout the brain. In a study in mice, the MIT team found that one of the main roles of noradrenaline, also known as norepinephrine, is to help the brain learn from surprising results.

“What this work shows is that the blue locus (locus coeruleus) encodes unexpected events, and paying attention to those sudden events is critical for the brain to assess its environment,” says Mrijanka Sorr, a Newton professor of neurosciences in the MIT Department of Brain and Cognition. for Science Tech, a member of MIT’s Pickwer Institute for Learning and Memory, and director of the Simmons Center for the Social Brain.

In addition to its role in signaling surprise, researchers have also discovered that noradrenaline helps motivate behavior that leads to reward, particularly in situations where there is uncertainty about offering a reward.

Suhr is the lead author of the new study, which appears today in temper nature. Vincent Britton Provencher, a former postdoctoral researcher at MIT who is now an assistant professor at Laval University, and Gabrielle Drummond, a graduate student at MIT, are the lead authors of this paper.

Behavior Modification

Noradrenaline is one of several neuromodulators that affect the brain, along with dopamine, serotonin, and acetylcholine. Unlike neurotransmitters, which allow cell-to-cell communication, neuromodulators are released over large areas of the brain, allowing them to exert more general effects.

“Neuromodulators are thought to irrigate large areas of the brain and thus alter the excitatory or inhibitory impulse received by neurons in a more point-to-point way,” says Sur. “This suggests that they must have very important brain-level functions that are important for survival and regulation of the brain’s state.”

While scientists have learned a lot about the role of dopamine in motivation and reward pursuit, little is known about other neuromodulators, including noradrenaline. It has been linked to agitation and increased alertness, but overuse of noradrenaline can lead to anxiety.

Previous studies of the blue locus, the brain’s primary source of norepinephrine, have shown that it receives input from many parts of the brain and transmits its signals widely. In the new study, the MIT team set out to study its role in a specific type of learning called reinforcement learning, or learning by trial and error.

In this study, researchers trained rats to push a 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 if they pressed the lever when they heard the low-frequency tone, they received an unpleasant puff of air.

The rats also learned to push the lever more forcefully when the tones were higher. When the volume was lower, they were more confident about whether or not they should pay. And when the researchers inhibited the activity of the blue locus, the mice became more reluctant to push the lever when they heard lower-volume tones, suggesting that noradrenaline promotes the opportunity for reward in situations where payoff is uncertain.

“The animal pays because it wants a reward, and the blue locus provides important cues to say, ‘Pay now, because the reward is coming,'” Sur says.

The researchers also found that neurons that generate the noradrenaline signal appear to send most of their output to the motor cortex, providing further evidence that this signal motivates the animals to take action.

surprise in sign

While this initial rush of noradrenaline appears to prompt the mice to take action, the researchers also found that the second rush of norepinephrine often occurs after the experiment ends. When the mice received an expected reward, these bursts were small. However, when the outcome of the trial was a surprise, the bursts were much larger. For example, when a rat received a puff of air instead of the reward it was expecting, the blue locus sent out a huge boost of noradrenaline.

In subsequent experiments, this rat would be less likely to push the lever when it was uncertain that it would receive a reward. “The animal is constantly adjusting its behavior,” Sohr says. “Although she has already learned the task, she adjusts her behavior based on what she just did.”

The mice also showed bursts of noradrenaline in the experiments when they received an unexpected reward. These bursts appear to spread noradrenaline to many parts of the brain, including the prefrontal cortex, where planning and other higher cognitive functions occur.

“The locus coeruleus appears to be more prevalent in the brain, and that might make sense because everything we do is modified by surprise,” Sohr says.

The researchers now plan to explore the potential synergy between noradrenaline and other neuromodulators, particularly dopamine, which also responds to unexpected rewards. They also hope to learn more about how the prefrontal cortex stores short-term memory inputs from the blue locus to help the animals improve their performance in future experiments.

The research was funded in part by Quebec Research Funds, the Natural Sciences and Engineering Research Council of Canada, the NARSAD Young Investigator Award from the Brain and Behavioral Research Foundation, the National Institutes of Health, the Simons Foundation Autism Research Initiative through the Simons Social Brain Center, and the National Natural Science Foundation of China and the NIH BRAIN Initiative.

2022-06-02 07:47:57

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