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Rhythmically stimulating the brain with electrical currents could boost cognitive function, according to analysis of over 100 studies

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Rhythmically stimulating the brain with electrical currents could boost cognitive function, according to analysis of over 100 studies

A meta-analysis helps resolve conflicting evidence on the of tACS.
Science Photo Library via Getty Images

Shrey Grover, Boston University

Figuring out how to enhance a person's mental capabilities has been of considerable interest to psychology and neuroscience researchers like me for decades. From improving attention in high-stakes environments, like traffic management, to reviving memory in people with dementia, the ability to improve cognitive function can have far-reaching consequences. New research suggests that brain stimulation could achieve the goal of boosting mental function.

In the Reinhart Lab at Boston , my colleagues and I have been examining the effects of an emerging brain stimulation technology – transcranial alternating current stimulation, or tACS – on different mental functions in and healthy people.

During this procedure, people wear an elastic cap embedded with electrodes that deliver weak electrical currents oscillating at specific frequencies to their scalp. By applying these controlled currents to specific brain regions, it is possible to alter brain activity by nudging neurons to fire rhythmically.

Another type of transcranial electric stimulation, tDCS, applies a direct electrical current to the brain.

Why would rhythmically firing neurons be beneficial? Research suggests that brain cells communicate effectively when they coordinate the rhythm of their firing. Critically, these rhythmic patterns of brain activity show marked abnormalities during neuropsychiatric illnesses. The purpose of tACS is to externally induce rhythmic brain activity that promotes healthy mental function, particularly when the brain might not be able to produce these rhythms on its own.

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However, tACS is a relatively new technology, and how it works is still unclear. Whether it can strengthen or revive brain rhythms to change mental function has been a topic of considerable debate in the field of brain stimulation. While some studies find evidence of changes in brain activity and mental function with tACS, others suggest that the currents typically used in people might be too weak to have a direct effect.

When with conflicting data in the scientific literature, it can be helpful to conduct a type of study called a meta-analysis that quantifies how consistent the evidence is across several studies. A previous meta-analysis conducted in 2016 found promising evidence for the use of tACS in changing mental function. However, the number of studies has more than doubled since then. The design of tACS technologies has also become increasingly sophisticated.

We set out to perform a new meta-analysis of studies using tACS to change mental function. To our knowledge, this work is the largest and most comprehensive meta-analysis yet on this topic, consisting of over 100 published studies with a combined total of more than 2,800 human participants.

Electrodes being placed on a person's head
Transcranial alternating current stimulation involves placing an electrode on a person's scalp.
J.M. Eddins Jr/U.S. Air Force via Flickr, CC BY-NC

After compiling over 300 measures of mental function across all the studies, we observed consistent and immediate improvement in mental function with tACS. When we examined specific cognitive functions, such as memory and attention, we observed that tACS produced the strongest improvements in executive function, or the ability to adapt in the face of new, surprising or conflicting information.

We also observed improvements in the ability to pay attention and to memorize information for both short and long periods of time. Together, these results suggest that tACS could particularly improve specific kinds of mental function, at least in the short term.

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To examine the effectiveness of tACS for those particularly vulnerable to changes in mental function, we examined the data from studies that included older adults and people with neuropsychiatric conditions. In both populations, we observed reliable evidence for improvements in cognitive function with tACS.

Interestingly, we also found that a specialized type of tACS that can target two brain regions at the same time and manipulate how they communicate with each other can both enhance or reduce cognitive function. This bidirectional effect on mental function could be particularly useful in the clinic. For example, some psychiatric conditions like depression may involve a reduced ability to rewards, while others like bipolar disorder may involve a highly active reward processing system. If tACS can change mental function in either direction, researchers may be able to develop flexible and targeted designs that cater to specific clinical needs.

Developments in the field of tACS are bringing researchers closer to being able to safely enhance mental function in a noninvasive way that doesn't require medication. Current statistical evidence across the literature suggests that tACS promise, and improving its design could help it produce stronger, long-lasting changes in mental function.The Conversation

Shrey Grover, Ph.D. Candidate in Psychological and Brain Sciences, Boston University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Cancer often requires more than one treatment − an oncologist explains why some patients like Kate Middleton receive both chemotherapy and surgery

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Cancer often requires more than one treatment − an oncologist explains why some patients like Kate Middleton receive both chemotherapy and surgery

Some cancer additional treatment after surgery with the goal of eliminating any remaining tumor cells.
BSIP/Collection Mix: Subjects via Getty Images

Alexander Olawaiye, University of Pittsburgh

When Kate Middleton, the princess of Wales, announced in March 2024 that she was receiving “preventive chemotherapy” abdominal surgery, many wondered what that entails. Formally known as adjuvant therapy, administering chemotherapy or other treatments after surgery is a common approach to treating certain types of cancer and is not necessarily intended to prevent cancer.

Oncologist Alexander Olawaiye of the of Pittsburgh explains what factors take into account when devising a cancer treatment plan.

Why are some cancers treated with surgery but not others?

There are many types of cancer treatment, including surgery, chemotherapy, radiotherapy, immunotherapy and hormonal therapy, among others. Sometimes doctors combine multiple types of treatment. Which is the best treatment approach depends on which organ the tumor originated from and how much the tumor has spread at the time of diagnosis.

Broadly speaking, there are two types of cancers: solid tumors – or visible tumors that can be seen by the naked eye or through imaging – and liquid tumors, such as blood cancers. The primary treatment for solid cancers is surgery to physically the tumor, with the goal of getting rid of all tissues involved with the tumor.

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For example, in ovarian cancer, surgery often includes removing the ovaries, fallopian tubes and the uterus, along with any visible cancer tissue in the rest of the belly. Sometimes this requires removing the spleen or part of the small intestine or liver.

Close-up of arm with IV line placed, resting on chair
For some cancer patients, systemic treatment such as chemotherapy may be a better option than surgery.
SeventyFour/iStock via Getty Images Plus

For skin cancers such as melanoma, surgery involves removing both the tumor and a good margin of normal-looking skin with it to capture any remaining cancer cells that may not be visible in the surrounding healthy skin. Likewise, a surgeon may also remove nearby lymph nodes.

When solid cancer is diagnosed early, the success of treatment following surgery is typically high. For example, an estimated 91% of cervical cancer patients who are diagnosed early are still alive at least five years after diagnosis. Endometrial cancer patients who are diagnosed early have an estimated five-year survival rate of 95%.

Why do some cancers recur?

Despite surgical removal, many tumors back. Researchers don't fully understand why cancers recur, but there are certain red flags that indicate the potential for recurrence.

One is how different the cancer cells look with healthy cells. The more different, the more aggressive the tumor. When a tumor is more aggressive, it's more likely to invade neighboring tissues and spread to other parts of the body.

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Another is the extent the cancer has spread at the time of diagnosis. This is what determines the stage of the cancer. For example, stage 1 cancer refers to a tumor that is confined to the organ it originally developed from. Stage 4 cancer refers to a tumor that has spread far from its origins to grow on other organs. The higher the stage, the higher the risk for a worse outcome.

A third factor is the organ where the cancer first originated. For instance, pancreatic cancers tend to be fatal even when diagnosed early because these tumors don't respond well to therapy. Ovarian cancer can have symptoms that are difficult to recognize, leading to late diagnoses. On the other hand, breast cancer and thyroid cancer tend to be less aggressive for longer periods of time, even when diagnosed at an advanced stage.

What is adjuvant and neoadjuvant therapy?

For patients with tumors that can be surgically removed, they often also receive chemotherapy or radiotherapy before or after the procedure. Doctors prescribe this additional, or adjuvant, treatment depending on the patient's risk of recurrence.

Recurrence typically happens when cancer cells escape from the tumor prior to or during surgical removal. Adjuvant chemotherapy or radiation after the procedure is aimed at killing these cells so they don't settle down and grow somewhere else in the body later on.

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In some cases, surgical removal is not feasible or not advisable. This could be because the cancer has spread so much that completely cutting it out is impossible or the risk of complications or disability from the surgery is high.

For example, primary surgery often isn't a good option for ovarian cancer, since most patients are diagnosed in advanced stages; complete surgical removal, even if possible, may involve removing important organs such as the rectum and colon. This can to the need for a colostomy or ileostomy, where stool is passed directly from the large or small intestine to a bag outside the belly. Surgical removal of breast cancer may mean losing the affected breast.

Team of surgeons operating on a patient
Some surgeries to remove tumors can lead to unwanted side effects or complications.
Gumpanat/iStock via Getty Images Plus

The risk of unwanted side effects from surgical removal can be reduced through neoadjuvant therapy, or administering chemotherapy or radiation before the procedure to shrink the tumor and reduce the amount of surgery required. Studies have shown that neoadjuvant therapy can ovarian cancer patients avoid colostomies after surgery and allow breast cancer patients to opt for a procedure that conserves their breast.

Neoadjuvant or adjuvant treatment can include chemotherapy, immunotherapy, hormonal therapy, radiation therapy or a combination of these treatments. Further advances in research will offer doctors and patients even more approaches to effectively treat cancer.The Conversation

Alexander Olawaiye, Professor of Obstetrics, Gynecology and Reproductive Sciences, University of Pittsburgh

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Horses lived in the Americas for millions of years – new research helps paleontologists understand the fossils we’ve found and those that are missing from the record

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Horses lived in the Americas for millions of years – new research helps paleontologists understand the fossils we've found and those that are missing from the record

People have collected fossil horses throughout North America for centuries.
Florida /Mary Warrick

Stephanie Killingsworth, University of Florida and Bruce J. MacFadden, University of Florida

Many people assume that horses first came to the Americas when Spanish explorers brought them here about 500 years ago. In fact, recent research has confirmed a European origin for horses associated with humans in the American Southwest and Great Plains.

But those weren't the first horses in North America. The Equidae, which includes domesticated varieties of horses and donkeys along with zebras and their kin, is actually native to the Americas. The fossil record reveals horse origins here more than 50 million years ago, as well as their extinction throughout the Americas during the last Ice Age about 10,000 years ago.

family tree showing horse evolution diversifying over time
Phylogeny, geographic distribution, diet and body sizes of the family Equidae over the past 55 million years.
From ‘Fossil horses–evidence for evolution.' Science. MacFadden, 2005. Reprinted with permission from AAAS.

We are paleontologists who focus our research on various types of fossils, including ancient horses. Our most recent work used computer statistics to analyze gaps in the fossil record to infer more about which horse species really did and didn't in one ancient habitat in Florida.

Horses evolved as ecosystems changed

People have collected fossil horses throughout North America for centuries. Because horse fossils are abundant and widespread across the continent, scientists often point to the long span of the horse family as evidence of long-term evolutionary change.

Paleontologists like us, who study extinct mammals, almost never find complete skeletons. Instead, we focus on durable fossil teeth, which help us understand ancient diets, and fossil limbs, which help clarify how these animals moved.

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Horses are eating machines. In the wild , they primarily feed on grasses that don't much nutrition, and thus they need to consume large quantities to survive. The large teeth of modern horses and their ancestors are adapted primarily for grazing on gritty grasses. They replaced smaller teeth of more primitive horses adapted to browsing on soft leafy vegetation.

We know what horses ate millions of years ago by studying distinctive microscopic scratches, pits and other wear patterns on their teeth that were created as the ancient horses chewed plant foods. And analyses of carbon preserved in fossil teeth show that coexisting horse species ate different plants; some browsed on leaves from bushes and trees, some grazed on grasses, and yet others were mixed feeders.

The change in tooth shape tracks the change in dominant vegetation types in North America, from tropical forests that then gave way to the great expansion of open prairie grasslands. As the climate and flora changed over millions of years, horses shifted from being largely forest-dwelling browsers to largely open-country grazers. Their teeth and feeding patterns adapted to the environment.

Another adaptation is visible on horses' feet. Modern horses have one hoofed toe on each . Many extinct fossil horses – the ancient ancestors of today's horses – had three toes per foot. The single toe on each elongated foot is good for rapid and sustained running to evade predators and for long-distance seasonal migrations. The more ancient three-toed feet provided stability on unstable or wet ground. The adaptation from three toes to one was likely in response to changing habitats.

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But even as the environment changed, one distinct species didn't completely replace another overnight. The fossil record in North America documents periods millions of years ago when multiple horse species coexisted on the ancient landscapes. Species were of different sizes and had teeth equipped for munching different plants, so they weren't competing directly for the same foods. Different habitats within these ancient ecosystems likely had some species more adapted to forests and others more adapted to grasslands.

Understanding Florida's fossil record

Paleontologists have been collecting horse fossils in Florida for over 125 years. The Florida Museum of Natural History at the of Florida, where we work, has more than 70,000 fossil horse specimens from more than a thousand locations across the .

One of our more prolific fossil sites, Montbrook, provides a glimpse of a 5.8 million-year-old ancient stream bed. It preserved more than 30 extinct mammals, including rhinos, elephants and carnivores, as well as hundreds of bones and teeth of fossil horses.

Although six horse species are known elsewhere in Florida, we have only found four so far at Montbrook. This smaller number of horse species perplexed us, so we decided to investigate. Did the two “missing” horse species truly not live at Montbrook, or have scientists simply not discovered their fossil remains yet?

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Representative fossil horse teeth of Florida
Each of the six fossil horse species (A-F) found in Florida have distinct teeth. Scale bar = 1 centimeter.
Killingsworth & MacFadden, Paleobiology, 2024, CC BY-NC-SA

We designed a theoretical model that compares Montbrook, with only four horse species, to other fossil sites in Florida that contain all six. Using a statistical technique that scientists call “bootstrapping,” our computer essentially simulated continued fossil collecting over time. We generated 1,000 theoretical fossil collection based on the fossil species counts from the sites where all six are present, to predict the probability of collecting the species that are currently missing at Montbrook.

Results from our simulation show that the two missing horse species at Montbrook were absent for different reasons. One of the horses is likely to be truly absent; the other may still be discovered with further excavation.

About a dozen people focused on digging in soil a few feet below the surface of surrounding landscape.
Excavations are ongoing at the Montbrook fossil site in Florida.
Florida Museum/Jeff Gage

Probing ‘gaps' in the fossil record

Knowing a species is absent is just as important as knowing when one is present at a fossil site. Absences may be indicators of underlying ecological and biological drivers changing population dynamics. Coupled with other types of analyses, researchers can apply this kind of predictive modeling across many fossil species and ancient landscapes.

Ever since Charles Darwin proposed his theory of evolution, scientists have known that the fossil record is incomplete, resulting in gaps in our knowledge of the ancient past and evolutionary change. Paleontologists are challenged to explain these gaps, including which species were or were not present at particular fossil sites.

Gaps can result from certain materials, such as teeth and shells, which are often more durable than porous bone, fossilizing better than others. Likewise, different chemical conditions during fossilization, and even the amount of time spent collecting fossils at a particular site, can contribute to the lack of knowledge.

Fortunately, fossil horse teeth preserve quite well and are commonly found. As new discoveries are made, such as those from our ongoing excavations in Florida, they'll help clarify and narrow gaps in the fossil record.The Conversation

Stephanie Killingsworth, Ph.D. Student in Geological Sciences, University of Florida and Bruce J. MacFadden, Distinguished Professor and Director of Thompson Earth Institute (TESI), University of Florida

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How AI and a popular card game can help engineers predict catastrophic failure – by finding the absence of a pattern

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How AI and a popular card game can help engineers predict catastrophic failure – by finding the absence of a pattern

Can you find a matching set?
Cmglee/Wikimedia Commons, CC BY-SA

John Edward McCarthy, Arts & Sciences at Washington University in St. Louis

Humans are very good at spotting patterns, or repeating features people can recognize. For instance, ancient Polynesians navigated across the Pacific by recognizing many patterns, from the ' constellations to more subtle ones such as the directions and sizes of ocean swells.

Very recently, mathematicians like me have started to study large collections of objects that have no patterns of a particular sort. How large can collections be before a specified pattern has to appear somewhere in the collection? Understanding such scenarios can have significant real-world implications: For example, what's the smallest number of server failures that would to the severing of the internet?

Research from mathematician Jordan Ellenberg at the of Wisconsin and researchers at Google's Deep Mind have proposed a novel approach to this problem. Their work uses artificial intelligence to find large collections that don't contain a specified pattern, which can us understand some worst-case scenarios.

Patterns in the card game Set

The idea of patternless collections can be illustrated by a popular card called Set. In this game, players lay out 12 cards, face up. Each card has a different simple picture on it. They vary in terms of number, color, shape and shading. Each of these four features can have one of three values.

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Players race to look for “sets,” which are groups of three cards in which every feature is either the same or different in each card. For instance, cards with one solid red diamond, two solid green diamonds and three solid purple diamonds form a set: All three have different numbers (one, two, three), the same shading (solid), different colors (red, green, purple) and the same shape (diamond).

Marsha Falco originally created the game Set to help explain her research on population genetics.

Finding a set is usually possible – but not always. If none of the players can find a set from the 12 cards on the table, then they flip over three more cards. But they still might not be able to find a set in these 15 cards. The players continue to flip over cards, three at a time, until someone spots a set.

So what is the maximum number of cards you can lay out without forming a set?

In 1971, mathematician Giuseppe Pellegrino showed that the largest collection of cards without a set is 20. But if you chose 20 cards at random, “no set” would happen only about one in a trillion times. And finding these “no set” collections is an extremely hard problem to solve.

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Finding ‘no set' with AI

If you wanted to find the smallest collection of cards with no set, you could in principle do an exhaustive search of every possible collection of cards chosen from the deck of 81 cards. But there are an enormous number of possibilities – on the order of 1024 (that's a “1” followed by 24 zeros). And if you increase the number of features of the cards from four to, say, eight, the complexity of the problem would overwhelm any computer doing an exhaustive search for “no set” collections.

Mathematicians love to think about computationally difficult problems like this. These complex problems, if approached in the right way, can become tractable.

It's easier to find best-case scenarios – here, that would mean the fewest number of cards that could contain a set. But there were few known strategies that could explore bad scenarios – here, that would mean a large collection of cards that do not contain a set.

Ellenberg and his collaborators approached the bad scenario with a type of AI called large language models, or LLMs. The researchers first wrote computer programs that generate some examples of collections of many that contain no set. These collections typically have “cards” with more than four features.

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Then they fed these programs to the LLM, which soon learned how to write many similar programs and choose the ones that give rise to the largest set- collections to undergo the again. Iterating that process by repeatedly tweaking the most successful programs enables them to find larger and larger set-free collections.

Square of nine circles, four of which are colored blue, connected by grey, red, green, and yellow lines
This is another version of a ‘no set,' where no three components of a set are linked by a line.
Romera-Peredes et al./Nature, CC BY-SA

This method allows people to explore disordered collections – in this instance, collections of cards that contain no set – in an entirely new way. It does not guarantee that researchers will find the absolute worst-case scenario, but they will find scenarios that are much worse than a random generation would yield.

Their work can help researchers understand how might align in a way that to catastrophic failure.

For example, how vulnerable is the electrical grid to a malicious attacker who destroys select substations? Suppose that a bad collection of substations is one where they don't form a connected grid. The worst-case scenario is now a very large number of substations that, when taken all together, still don't yield a connected grid. The amount of substations excluded from this collection make up the smallest number a malicious actor needs to destroy to deliberately disconnect the grid.

The work of Ellenberg and his collaborators demonstrates yet another way that AI is a very powerful tool. But to solve very complex problems, at least for now, it still needs human ingenuity to guide it.The Conversation

John Edward McCarthy, Professor of Mathematics, Arts & Sciences at Washington University in St. Louis

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