Sleep Clearance? - Counting Crows - Cortical Mysteries - Depressed Brain

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May 25, 2024, 7:14:16 AMMay 25

https://www.thetransmitter.org/glymphatic-system/new-method-reignites-controversy-over-brain-clearance-during-sleep/

New method reignites controversy over brain clearance during sleep

By Elissa Welle

A new study suggests that the brain clears less waste during sleep and under anesthesia than while in other states—directly contradicting prior results that suggest sleep initiates that process. The findings are stirring fresh debate on social media and elsewhere over the glymphatic system hypothesis, which contends that convective flow of cerebrospinal fluid clears the sleeping brain of toxins.

The new work, published 13 May in Nature Neuroscience, proposes that fluid diffusion is responsible for moving waste throughout the brain. It uses a different method than the earlier studies—injecting tracers into mouse brain tissue instead of cerebrospinal fluid—which is likely a more reliable way to understand how the fluid moves through densely packed neurons, says Jason Rihel, professor of behavioral genetics at University College London, who was not involved in any of the studies on brain clearance.

The findings have prompted some sleep researchers, including Rihel, to question the existence of a glymphatic system and whether brain clearance is tied to sleep-wake states, he says.

But leading proponents of the sleep-induced clearance theory are pushing back against the study’s techniques. The new study is “misleading” and “extremely poorly done,” says Maiken Nedergaard, professor of neurology at the University of Rochester Medical Center, whose 2013 study on brain clearance led to the hypothesis of a glymphatic system. She says she plans to challenge the work in a proposed Matters Arising commentary for Nature Neuroscience.

Inserting needles into the brain damages the tissue, and injecting fluid, as the team behind the new work did, increases intracranial pressure, says Jonathan Kipnis, professor of pathology and immunology at Washington University School of Medicine in St. Louis. Kipnis and his colleagues published a study in February in support of the glymphatic system hypothesis that suggests neural activity facilitates brain clearance.

“You disturb the system when you inject into the brain,” Kipnis says, “and that’s why we were always injecting in the CSF.”
© 2024 Simons Foundation
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https://www.nature.com/articles/d41586-024-01482-x

These crows have counting skills previously only seen in people

By Mariana Lenharo

Crows know their numbers. An experiment has revealed that these birds can count their own calls, showcasing a numerical skill previously only seen in people.

Investigating how animals understand numbers can help scientists to explore the biological origins of humanity’s numerical abilities, says Giorgio Vallortigara, a neuroscientist at the University of Trento in Rovereto, Italy. Being able to produce a deliberate number of vocalizations on cue, as the birds in the experiment did, “is actually a very impressive achievement”, he notes.

Andreas Nieder, an animal physiologist at the University of Tübingen in Germany and a co-author of the study published 23 May in Science1, says it was amazing to see how cognitively flexible these corvids are. “They have a reputation of being very smart and intelligent, and they proved this once again.”

The researchers worked with three carrion crows (Corvus corone) that had already been trained to caw on command. Over the next several months, the birds were taught to associate visual cues — a screen showing the digits 1, 2, 3 or 4 — with the number of calls they were supposed to produce. They were later also introduced to four auditory cues that were each associated with a distinct number.

During the experiment, the birds stood in front of the screen and were presented with a visual or auditory cue. They were expected to produce the number of vocalizations associated with the cue and to peck at an ‘enter key’ on the touchscreen monitor when they were done. If they got it right, an automated feeder delivered bird-seed pellets and mealworms as a reward.

They were correct most of the time. “Their performance was way beyond chance and highly significant,” says Nieder.

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https://www.quantamagazine.org/what-happens-in-the-brain-to-cause-depression-20240523/

What Happens in the Brain to Cause Depression?

By Steven Strogatz

For decades, the best drug therapies for treating depression, like SSRIs, have been based on the idea that depressed brains don’t have enough of the neurotransmitter serotonin. Yet for almost as long, it’s been clear that simplistic theory is wrong. Recent research into the true causes of depression is finding clues in other neurotransmitters and the realization that the brain is much more adaptable than scientists once imagined. Treatments for depression are being reinvented by drugs like ketamine that can help regrow synapses, which can in turn restore the right brain chemistry and improve whole body health.

In this episode, John Krystal, a neuropharmacologist at the Yale School of Medicine, shares the new findings in mental health research that are revolutionizing psychiatric medication.

STEVEN STROGATZ: According to the World Health Organization, 280 million people worldwide suffer from depression. For decades, people with chronic depression have been told their problem lies with a chemical imbalance in the brain, specifically a deficit in a neurotransmitter called serotonin. And based on this theory, many have been prescribed antidepressants known as selective serotonin reuptake inhibitors, or SSRIs, to correct this chemical imbalance.

This theory has become the common narrative, yet almost from the beginning, researchers have questioned the role of serotonin in depression, even though SSRIs do seem to bring a lot of relief to many people.

So, if bad brain chemistry isn’t at the root of chronic depression, what is? If the thinking behind SSRIs is wrong, why do they seem to help? And is it possible that as we get closer to the true cause of depression, we may find better treatments for other conditions as well?

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https://www.sciencenews.org/article/biological-puzzles-human-brain-visual

Biological puzzles abound in an up-close look at a human brain

By Laura Sanders

It’s a bit like seeing a world in a grain of sand.

Except the view, in this case, is the exquisite detail inside a bit of human brain about half the size of a grain of rice. Held in that minuscule object is a complex collective of cells, blood vessels, intricate patterns and biological puzzles.

Scientists had hints of these mysteries in earlier peeks at this bit of brain (SN: 6/29/21). But now, those details have been brought into new focus by mapping the full landscape of some 57,000 cells, 150 million synapses and their accompanying 23 centimeters of blood vessels, researchers report in the May 10 Science. The full results, the scientists hope, may lead to greater insights into how the human brain works.

“We’re going in and looking at every individual connection attached to every cell — a very high level of detail,” says Viren Jain, a computational neuroscientist at Google Research in Mountain View, Calif. The big-picture goal of brain mapping efforts, he says, is “to understand how human brains work and what goes wrong in various kinds of brain diseases.”

The newly mapped brain sample was removed during a woman’s surgery for epilepsy, so that doctors could reach a deeper part of the brain. The bit, donated with the woman’s consent, was from the temporal lobe of the cortex, the outer part of the brain involved in complex mental feats like thinking, remembering and perceiving.
This digital drawing of a person's head shows the brain inside. An arrow points to the bottom left side of the brain.

After being fixed in a preservative, the brain bit was sliced into almost impossibly thin wisps, and then each slice was imaged with a high-powered microscope. Once these views were collected, researchers used computers to digitally reconstruct the three-dimensional objects embedded in the piece of brain.
© Society for Science & the Public 2000–2024
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https://www.washingtonpost.com/wellness/2024/05/23/marijuana-cannabis-alcohol-drinking-daily/

Marijuana surpasses alcohol in daily use for Americans

By Jennifer Hassan

More people in the United States say they are using marijuana daily or near daily, compared with people who say they are drinking alcohol that often, according to a new study.

In 2022, about 17.7 million people reported daily or near-daily marijuana use, compared with 14.7 million people who reported drinking at the same frequency, said the report, which was based on more than four decades of data from the National Survey on Drug Use and Health. It was the first time the survey recorded more frequent users of cannabis than alcohol, the report added.

The research was published Wednesday in the peer-reviewed journal Addiction. The research window spans the years 1979 to 2022, and the 27 surveys that were analyzed involved more than 1.6 million participants during that time frame.

The study described the growth in daily or near-daily cannabis use as “striking.” While “far more people drink” than use marijuana, high-frequency drinking among Americans is less common, the report said. The 2022 survey found that the median drinker reported drinking on four to five days in a month, compared with 15 to 16 days in a month for cannabis.

The study noted that changing trends in cannabis use “parallel corresponding changes in cannabis policy, with declines during periods of greater restriction and growth during periods of policy liberalization.” It stressed, however, that this did not mean there was a causal link, as “both could have been manifestations of changes in underlying culture and attitudes.”

Thirty-eight states and D.C. have legalized medical marijuana programs, and 24 states have approved recreational cannabis use.