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Study reveals a universal pattern of brain wave frequencies
Throughout the brain’s cortex, neurons are arranged in six distinctive layers, which can be readily seen with a microscope. A team of MIT neuroscientists has now found that these layers also show distinct patterns of electrical activity, which are consistent over many brain regions and across several animal species, including humans.
“When you see something that consistent and ubiquitous across cortex, it’s playing a very fundamental role in what the cortex does,” says Earl Miller, the Picower Professor of Neuroscience, a member of MIT’s Picower Institute for Learning and Memory, and one of the senior authors of the new study.
Imbalances in how these oscillations interact with each other may be involved in brain disorders such as attention deficit hyperactivity disorder, the researchers say.
“Overly synchronous neural activity is known to play a role in epilepsy, and now we suspect that different pathologies of synchrony may contribute to many brain disorders, including disorders of perception, attention, memory, and motor control. In an orchestra, one instrument played out of synchrony with the rest can disrupt the coherence of the entire piece of music,” says Robert Desimone, director of MIT’s McGovern Institute for Brain Research and one of the senior authors of the study.
André Bastos, an assistant professor of psychology at Vanderbilt University, is also a senior author of the open-access paper, which appears today in Nature Neuroscience. The lead authors of the paper are MIT research scientist Diego Mendoza-Halliday and MIT postdoc Alex Major.
Layers of activity
The human brain contains billions of neurons, each of which has its own electrical firing patterns. Together, groups of neurons with similar patterns generate oscillations of electrical activity, or brain waves, which can have different frequencies. Miller’s lab has previously shown that high-frequency gamma rhythms are associated with encoding and retrieving sensory information, while low-frequency beta rhythms act as a control mechanism that determines which information is read out from working memory.
His lab has also found that in certain parts of the prefrontal cortex, different brain layers show distinctive patterns of oscillation: faster oscillation at the surface and slower oscillation in the deep layers. One study, led by Bastos when he was a postdoc in Miller’s lab, showed that as animals performed working memory tasks, lower-frequency rhythms generated in deeper layers regulated the higher-frequency gamma rhythms generated in the superficial layers.
In addition to working memory, the brain’s cortex also is the seat of thought, planning, and high-level processing of emotion and sensory information. Throughout the regions involved in these functions, neurons are arranged in six layers, and each layer has its own distinctive combination of cell types and connections with other brain areas.
“The cortex is organized anatomically into six layers, no matter whether you look at mice or humans or any mammalian species, and this pattern is present in all cortical areas within each species,” Mendoza-Halliday says. “Unfortunately, a lot of studies of brain activity have been ignoring those layers because when you record the activity of neurons, it’s been difficult to understand where they are in the context of those layers.”
In the new paper, the researchers wanted to explore whether the layered oscillation pattern they had seen in the prefrontal cortex is more widespread, occurring across different parts of the cortex and across species.
Using a combination of data acquired in Miller’s lab, Desimone’s lab, and labs from collaborators at Vanderbilt, the Netherlands Institute for Neuroscience, and the University of Western Ontario, the researchers were able to analyze 14 different areas of the cortex, from four mammalian species. This data included recordings of electrical activity from three human patients who had electrodes inserted in the brain as part of a surgical procedure they were undergoing.
Recording from individual cortical layers has been difficult in the past, because each layer is less than a millimeter thick, so it’s hard to know which layer an electrode is recording from. For this study, electrical activity was recorded using special electrodes that record from all of the layers at once, then feed the data into a new computational algorithm the authors designed, termed FLIP (frequency-based layer identification procedure). This algorithm can determine which layer each signal came from.
“More recent technology allows recording of all layers of cortex simultaneously. This paints a broader perspective of microcircuitry and allowed us to observe this layered pattern,” Major says. “This work is exciting because it is both informative of a fundamental microcircuit pattern and provides a robust new technique for studying the brain. It doesn’t matter if the brain is performing a task or at rest and can be observed in as little as five to 10 seconds.”
Across all species, in each region studied, the researchers found the same layered activity pattern.
“We did a mass analysis of all the data to see if we could find the same pattern in all areas of the cortex, and voilà, it was everywhere. That was a real indication that what had previously been seen in a couple of areas was representing a fundamental mechanism across the cortex,” Mendoza-Halliday says.
Maintaining balance
The findings support a model that Miller’s lab has previously put forth, which proposes that the brain’s spatial organization helps it to incorporate new information, which carried by high-frequency oscillations, into existing memories and brain processes, which are maintained by low-frequency oscillations. As information passes from layer to layer, input can be incorporated as needed to help the brain perform particular tasks such as baking a new cookie recipe or remembering a phone number.
“The consequence of a laminar separation of these frequencies, as we observed, may be to allow superficial layers to represent external sensory information with faster frequencies, and for deep layers to represent internal cognitive states with slower frequencies,” Bastos says. “The high-level implication is that the cortex has multiple mechanisms involving both anatomy and oscillations to separate ‘external’ from ‘internal’ information.”
Under this theory, imbalances between high- and low-frequency oscillations can lead to either attention deficits such as ADHD, when the higher frequencies dominate and too much sensory information gets in, or delusional disorders such as schizophrenia, when the low frequency oscillations are too strong and not enough sensory information gets in.
“The proper balance between the top-down control signals and the bottom-up sensory signals is important for everything the cortex does,” Miller says. “When the balance goes awry, you get a wide variety of neuropsychiatric disorders.”
The researchers are now exploring whether measuring these oscillations could help to diagnose these types of disorders. They are also investigating whether rebalancing the oscillations could alter behavior — an approach that could one day be used to treat attention deficits or other neurological disorders, the researchers say.
The researchers also hope to work with other labs to characterize the layered oscillation patterns in more detail across different brain regions.
“Our hope is that with enough of that standardized reporting, we will start to see common patterns of activity across different areas or functions that might reveal a common mechanism for computation that can be used for motor outputs, for vision, for memory and attention, et cetera,” Mendoza-Halliday says.
The research was funded by the U.S. Office of Naval Research, the U.S. National Institutes of Health, the U.S. National Eye Institute, the U.S. National Institute of Mental Health, the Picower Institute, a Simons Center for the Social Brain Postdoctoral Fellowship, and a Canadian Institutes of Health Postdoctoral Fellowship.
An experimental drug originally developed to treat cancer may help clear HIV from infected cells in the brain, according to a new Tulane University study.
Published in the journal Brain, this discovery marks a significant step toward eliminating HIV from hard-to-reach reservoirs where the virus evades otherwise effective treatment.
“This research is an important step in tackling brain-related issues caused by HIV, which still affect people even when they are on effective HIV medication,” said lead study author Woong-Ki Kim, PhD, associate director for research at Tulane National Primate Research Center. “By specifically targeting the infected cells in the brain, we may be able to clear the virus from these hidden areas, which has been a major challenge in HIV treatment.”
Antiretroviral therapy (ART) is an essential component of successful HIV treatment, maintaining the virus at undetectable levels in the blood and transforming HIV from a terminal illness into a manageable condition. However, ART does not completely eradicate HIV, necessitating lifelong treatment. The virus persists in “viral reservoirs” in the brain, liver, and lymph nodes, where it remains out of reach of ART.
The brain has been a particularly challenging area for treatment due to the blood-brain barrier — a protective membrane that shields it from harmful substances but also blocks treatments, allowing the virus to persist. In addition, cells in the brain known as macrophages are extremely long-lived, making them difficult to eradicate once they become infected.
Infection of macrophages is thought to contribute to neurocognitive dysfunction, experienced by nearly half of those living with HIV. Eradicating the virus from the brain is critical for comprehensive HIV treatment and could significantly improve the quality of life for those with HIV-related neurocognitive problems.
Researchers focused on macrophages, a type of white blood cell that harbors HIV in the brain. By using a small molecule inhibitor to block a receptor that increases in HIV-infected macrophages, the team successfully reduced the viral load in the brain. This approach essentially cleared the virus from brain tissue, providing a potential new treatment avenue for HIV.
The small molecule inhibitor used, BLZ945, has previously been studied for therapeutic use in amyotrophic lateral sclerosis (ALS) and brain cancer, but never before in the context of clearing HIV from the brain.
The study, which took place at the Tulane National Primate Research Center, utilized three groups to model human HIV infection and treatment: an untreated control group, and two groups treated with either a low or high dose of the small molecule inhibitor for 30 days. The high-dose treatment lead to a notable reduction in cells expressing HIV receptor sites, as well as a 95-99% decrease in viral DNA loads in the brain .
In addition to reducing viral loads, the treatment did not significantly impact microglia, the brain’s resident immune cells, which are essential for maintaining a healthy neuroimmune environment. It also did not show signs of liver toxicity at the doses tested.
The next step for the research team is to test this therapy in conjunction with ART to assess its efficacy in a combined treatment approach. This could pave the way for more comprehensive strategies to eradicate HIV from the body entirely.
This research was funded by the National Institutes of Health, including grants from the National Institute of Mental Health and the National Institute of Neurological Disorders and Stroke, and was supported with resources from the Tulane National Primate Research Center base grant of the National Institutes of Health, P51 OD011104.
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Chemical analyses find hidden elements from renaissance astronomer Tycho Brahe’s alchemy laboratory
In the Middle Ages, alchemists were notoriously secretive and didn’t share their knowledge with others. Danish Tycho Brahe was no exception. Consequently, we don’t know precisely what he did in the alchemical laboratory located beneath his combined residence and observatory, Uraniborg, on the now Swedish island of Ven.
However, during an excavation in 1988-1990, some pottery and glass shards were found in Uraniborg’s old garden. These shards were believed to originate from the basement’s alchemical laboratory. Five of these shards — four glass and one ceramic — have now undergone chemical analyses to determine which elements the original glass and ceramic containers came into contact with.
The chemical analyses were conducted by Professor Emeritus and expert in archaeometry, Kaare Lund Rasmussen from the Department of Physics, Chemistry, and Pharmacy, University of Southern Denmark. Senior researcher and museum curator Poul Grinder-Hansen from the National Museum of Denmark oversaw the insertion of the analyses into historical context.
Enriched levels of trace elements were found on four of them, while one glass shard showed no specific enrichments. The study has been published in the journal Heritage Science.
“Most intriguing are the elements found in higher concentrations than expected — indicating enrichment and providing insight into the substances used in Tycho Brahe’s alchemical laboratory,” said Kaare Lund Rasmussen.
The enriched elements are nickel, copper, zinc, tin, antimony, tungsten, gold, mercury, and lead, and they have been found on either the inside or outside of the shards.
Most of them are not surprising for an alchemist’s laboratory. Gold and mercury were — at least among the upper echelons of society — commonly known and used against a wide range of diseases.
“But tungsten is very mysterious. Tungsten had not even been described at that time, so what should we infer from its presence on a shard from Tycho Brahe’s alchemy workshop?,” said Kaare Lund Rasmussen.
Tungsten was first described and produced in pure form more than 180 years later by the Swedish chemist Carl Wilhelm Scheele. Tungsten occurs naturally in certain minerals, and perhaps the element found its way to Tycho Brahe’s laboratory through one of these minerals. In the laboratory, the mineral might have undergone some processing that separated the tungsten, without Tycho Brahe ever realizing it.
However, there is also another possibility that Professor Kaare Lund Rasmussen emphasizes has no evidence whatsoever — but which could be plausible.
Already in the first half of the 1500s, the German mineralogist Georgius Agricola described something strange in tin ore from Saxony, which caused problems when he tried to smelt tin. Agricola called this strange substance in the tin ore “Wolfram” (German for Wolf’s froth, later renamed to tungsten in English).
“Maybe Tycho Brahe had heard about this and thus knew of tungsten’s existence. But this is not something we know or can say based on the analyses I have done. It is merely a possible theoretical explanation for why we find tungsten in the samples,” said Kaare Lund Rasmussen.
Tycho Brahe belonged to the branch of alchemists who, inspired by the German physician Paracelsus, tried to develop medicine for various diseases of the time: plague, syphilis, leprosy, fever, stomach aches, etc. But he distanced himself from the branch that tried to create gold from less valuable minerals and metals.
In line with the other medical alchemists of the time, he kept his recipes close to his chest and shared them only with a few selected individuals, such as his patron, Emperor Rudolph II, who allegedly received Tycho Brahe’s prescriptions for plague medicine.
We know that Tycho Brahe’s plague medicine was complicated to produce. It contained theriac, which was one of the standard remedies for almost everything at the time and could have up to 60 ingredients, including snake flesh and opium. It also contained copper or iron vitriol (sulphates), various oils, and herbs.
After various filtrations and distillations, the first of Brahe’s three recipes against plague was obtained. This could be made even more potent by adding tinctures of, for example, coral, sapphires, hyacinths, or potable gold.
“It may seem strange that Tycho Brahe was involved in both astronomy and alchemy, but when one understands his worldview, it makes sense. He believed that there were obvious connections between the heavenly bodies, earthly substances, and the body’s organs. Thus, the Sun, gold, and the heart were connected, and the same applied to the Moon, silver, and the brain; Jupiter, tin, and the liver; Venus, copper, and the kidneys; Saturn, lead, and the spleen; Mars, iron, and the gallbladder; and Mercury, mercury, and the lungs. Minerals and gemstones could also be linked to this system, so emeralds, for example, belonged to Mercury,” explained Poul Grinder-Hansen.
Kaare Lund Rasmussen has previously analyzed hair and bones from Tycho Brahe and found, among other elements, gold. This could indicate that Tycho Brahe himself had taken medicine that contained potable gold.
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Nitrogen emissions have a net cooling effect: But researchers warn against a climate solution
An international team of researchers has found that nitrogen emissions from fertilisers and fossil fuels have a net cooling effect on the climate. But they warn increasing atmospheric nitrogen has further damaging effects on the environment, calling for an urgent reduction in greenhouse gas emissions to halt global warming.
The paper was led by the Max Planck Institute in Germany and included authors from the University of Sydney. It comes one day after new data from the European Union’s Copernicus Climate Change Service indicated that Sunday, 21 July was the hottest day recorded in recent history.
The net cooling effect occurs in four ways:
- Short-lived nitrogen oxides produced by the combustion of fossil fuels pollute the atmosphere by forming fine suspended particles which shield sunlight, in turn cooling the climate;
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ammonia (a nitrogen and hydrogen-based compound) released into the atmosphere from the application of manure and artificial fertilisers has a similar effect;
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nitrogen applied to crops allows plants to grow more abundantly, absorbing more CO2 from the atmosphere, enabling a cooling effect;
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nitrogen oxides also play a role in the breakdown of atmospheric methane, a potent greenhouse gas.
The researchers warned that increasing atmospheric nitrogen was not a solution for combatting climate change.
“Nitrogen fertilisers pollute water and nitrogen oxides from fossil fuels pollute the air. Therefore, increasing rates of nitrogen in the atmosphere to combat climate change is not an acceptable compromise, nor is it a solution,” said Professor Federico Maggi from the University of Sydney’s School of Civil Engineering.
Sönke Zaehle from the Max Planck Institute said: “This may sound like good news, but you have to bear in mind that nitrogen emissions have many harmful effects, for example on health, biodiversity and the ozone layer. The current findings, therefore, are no reason to gloss over the harmful effects, let alone see additional nitrogen input as a means of combatting global warming.”
Elemental nitrogen, which makes up around 78 percent of the air, is climate-neutral, but other reactive nitrogen compounds can have direct or indirect effects on the global climate — sometimes warming and at other times cooling. Nitrous oxide (N2O) is an almost 300 times more potent greenhouse gas than CO2. Other forms of nitrogen stimulate the formation of ozone in the troposphere, which is a potent greenhouse gas and enhances global warming.
Professor Maggi said the research was important as it helped the team gain an understanding of the net-effect of the distribution of nitrogen emissions from agriculture.
“This work is an extraordinary example of how complex interactions at planetary scales cannot be captured with simplistic assessment tools. It shows the importance of developing mathematical models that can show the emergence of nonlinear — or unproportional — effects across soil, land, and atmosphere,” he said.
“Even if it appears counter-intuitive, reactive nitrogen introduced in the environment, mostly as agricultural fertilisers, can reduce total warming. However, this is minor compared with the reduction in greenhouse gas emissions required to keep the planet within safe and just operational boundaries.
“New generation computational tools are helping drive new learnings in climate change science, but understanding is not enough — we must act with great urgency to reduce greenhouse gas emissions.”
Gaining a holistic understanding of the impacts of nitrogen
The scientists determined the overall impact of nitrogen from human sources by first analysing the quantities of the various nitrogen compounds that end up in soil, water and air.
They then fed this data into models that depict the global nitrogen cycle and the effects on the carbon cycle, for example the stimulation of plant growth and ultimately the CO2 and methane content of the atmosphere. From the results of these simulations, they used another atmospheric chemistry model to calculate the effect of man-made nitrogen emissions on radiative forcing, that is the radiant energy that hits one square metre of the Earth’s surface per unit of time.
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