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Arthur T Knackerbracket has processed the following story:

According to a new research study, your brain can send out a burst of norepinephrine when it needs you to pay attention to something important.

When your brain needs you to pay attention to something important, one way it can do that is to send out a burst of noradrenaline, according to a new MIT study.

This neuromodulator, produced by a structure deep in the brain called the locus coeruleus, can have widespread effects throughout the brain. In a study of mice, the MIT team found that one key role of noradrenaline, also known as norepinephrine, is to help the brain learn from surprising outcomes.

“What this work shows is that the locus coeruleus encodes unexpected events, and paying attention to those surprising events is crucial for the brain to take stock of its environment,” says Mriganka Sur, the Newton Professor of Neuroscience in MIT’s Department of Brain and Cognitive Sciences, a member of MIT’s Picower Institute for Learning and Memory, and director of the Simons Center for the Social Brain.

In addition to its role in signaling surprise, the researchers also discovered that noradrenaline helps to stimulate behavior that leads to a reward, particularly in situations where there is uncertainty over whether a reward will be offered.

[...] Previous studies of the locus coeruleus, the brain’s primary source of noradrenaline, have shown that it receives input from many parts of the brain and also sends its signals far and wide. 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.

For this study, the researchers trained mice 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 pushed the lever when they heard a low-frequency tone, they received an unpleasant puff of air.

The mice also learned to push the lever harder when the tones were louder. When the volume was lower, they were more uncertain about whether they should push or not. And, when the researchers inhibited activity of the locus coeruleus, the mice became much more hesitant to push the lever when they heard low volume tones, suggesting that noradrenaline promotes taking a chance on getting a reward in situations where the payoff is uncertain.

“The animal is pushing because it wants a reward, and the locus coeruleus provides critical signals to say, push now, because the reward will come,” Sur says.

The researchers also found that the neurons that generate this noradrenaline signal appear to send most of their output to the motor cortex, which offers more evidence that this signal stimulates the animals to take action.

[...] The researchers now plan to explore the possible synergy between noradrenaline and other neuromodulators, especially dopamine, which also responds to unexpected rewards. They also hope to learn more about how the prefrontal cortex stores the short-term memory of the input from the locus coeruleus to help the animals improve their performance in future trials.

Reference: “Spatiotemporal dynamics of noradrenaline during learned behaviour” by Vincent Breton-Provencher, Gabrielle T. Drummond, Jiesi Feng, Yulong Li and Mriganka Sur, 1 June 2022, Nature.
DOI: 10.1038/s41586-022-04782-2

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