Saturday, December 3, 2022

Brain ‘background noise’ can be significant after all

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During a sleep Research Symposium in January 2020, Janna Lendner presented findings that suggest a way to look at people’s brain activity for signs of the borderline between arousal and unconsciousness. For patients who are comatose or under anesthesia, it can be very important for doctors to make this distinction correctly. This is trickier than it sounds, however, because when a person is in a REM sleep (REM) dream state, their brain produces the same familiar, gently oscillating brain waves as when they are awake.

Lendner argued, however, that the answer is not in regular brain waves, but rather in an aspect of neural activity that scientists might normally ignore: erratic background noise.

Some researchers seemed in disbelief. “They said, ‘So you’re telling me there’s, like, information in the noise?’” Said Lendner, an anesthesiology resident at the University Medical Center in Tübingen, Germany, who has recently completed a post-doctorate at the University of California, Berkeley. “I said yes. Someone’s noise is another’s signal. ”

Lendner is one of a growing number of neuroscientists who are stimulated by the idea that the noise in the brain’s electrical activity may contain new clues about its internal workings. What was once thought to be the neurological equivalent of annoying TV static may have profound implications for the way scientists study the brain.

Skeptics told neuroscientist Bradley Voytek that there was nothing to study in these noisy features of brain activity. But his own studies of changes in electrical noise as people get older, along with previous literature on statistical trends in irregular brain activity, convinced him that something was missing. So he spent years working on a way to help scientists rethink their data.

“It’s not enough to go in front of a group of scientists and say, ‘Hey, I think we did it wrong,’ said Voytek, associate professor of cognitive science and data science at the University of California, San Diego “You have to give them a new tool to do things” differently or better.

Bradley Voytek, associate professor of cognitive science and data science at the University of California, San Diego, helped bring attention to the importance of aperiodic activity in the brain by developing software to study it .Photography: Jessica Voytek

Working with neuroscientists at UC San Diego and Berkeley, Voytek developed software that isolates regular oscillations – like alpha waves, which are studied in depth in both sleeping and awake subjects – hiding in aperiodic parts of the body. brain activity. This gives neuroscientists a new tool to dissect both regular waves and aperiodic activity in order to unravel their roles in behavior, cognition, and disease.

The phenomenon that Voytek and other scientists are studying in different ways goes by many names. Some call it “the 1 /F slope ”or“ activity without ladder ”; Voytek pushed to rename it “aperiodic signal” or “aperiodic activity”.

It’s not just a brain quirk. The patterns that Lendner, Voytek, and others are researching relate to a phenomenon that scientists began to notice in complex systems across the natural world and technology in 1925. The statistical structure mysteriously appears in so many different contexts that some scientists even believe that it represents a law of unknown nature.

Although published studies have looked at arrhythmic brain activity for more than 20 years, no one has been able to establish what this really means. Now, however, scientists have better tools to isolate aperiodic signals in new experiments and to examine older data more deeply. Thanks to Voytek’s algorithm and other methods, a multitude of studies published in recent years have been carried out with the idea that aperiodic activity contains hidden treasures that can advance the study of aging, sleep, childhood development and more.

What is aperiodic activity?

Our bodies cycle to familiar rhythms of heartbeats and breaths – persistent cycles essential to survival. But there are equally vital drumbeats in the brain that don’t seem to have a pattern, and they may hold new clues about the foundations of behavior and cognition.

When a neuron sends a chemical called glutamate to another neuron, it makes the recipient more likely to fire; this scenario is called excitement. Conversely, if a neuron spits out the neurotransmitter gamma-aminobutyric acid, or GABA, the recipient neuron becomes less likely to fire; it is inhibition. Too much of either has consequences: deranged arousal leads to convulsions, while inhibition characterizes sleep and, in more extreme cases, coma.


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