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Adult-made neurons mature longer, have unique functions
Unraveling the mysteries of adult neurogenesis may have clinical applications.
- Neuroscientists don't know the degree to which adult human brains generate new neurons.
- A new study found that adult-born neurons in lab rats continued to grow and mature long after infant-born ones stopped.
- Understanding the process of neuron birth and death can help scientists understand the causes of neurological disorders.
Learning about the brain is a challenge. Neuroscientists must measure the operations of a byzantine tool with the very tool they're attempting to measure. That's a journey that's not so much winding as it is Möbius, so it's little wonder that history's greatest scientists and philosophers have yet to crack, say, the hard problem of consciousness.
Other problems are limited more by our inability to poke around in real-time. Take the question of adult neurogenesis. Neurogenesis is the brain's ability to generate new neurons. This process is intensely productive during embryonic development, and it continues after birth at a rate any parent with a toddler can appreciate daily.
For much of the 20th century, scientists believed neurogenesis didn't take place in the structured, sedate brains of human adults. They thought that after development we possessed all the neurons we'd ever have, and this lead to a perception that aged minds had less plasticity.
Then studies began to accumulate evidence that the adult brain may not be as placid as thought. One such study, published in 2018 in Cell Stem Cell, autopsied the hippocampi of 28 adults and found human brains still churn out neural stem cells by the thousands well into our golden years.
"We found that older people have similar ability to make thousands of hippocampal new neurons from progenitor cells as younger people do," Maura Boldrini, the study's lead author, said in a release. "We also found equivalent volumes of the hippocampus (a brain structure used for emotion and cognition) across ages."
Other studies have clouded the consensus. A study published in Nature, one with a remarkably similar methodology to Boldrini's, found little evidence for young neurons in the dentate gyrus, a part of the hippocampus. Its authors concluded that neurogenesis likely ceased, or was extremely rare, in adults.
But a new study published in the Journal of Neuroscience may have discovered how adult brains can continue to mature and retain plasticity without producing bubbly, baby neurons at the same clip as their younger counterparts.
Getting better with age
Reconstructions of adult-born neurons from rats undergoing maturation. Left to right: 2-weeks old, 4-weeks, 6-weeks, and 24-weeks.
One challenge to understanding adult neurogenesis is that most studies examine new neurons within their typical six-week development window. During that time a neuron is born, travels to the region of the brain where it will work, and differentiates depending on that location. After that, the neuron is considered mature.
According to Jason Snyder, a researcher at the Djavad Mowafaghian Centre for Brain Health and one of the study's authors, the researchers wanted to look beyond this window. They wanted to know if adult-born neurons could mature, grow later in life, and become unique to those produced by newborns' brains.
To test their hypothesis, the researchers injected a viral vector into lab rats' dentate gyri. The retrovirus was tagged with fluorescent reporters. After it inserted a copy of its genome into the dividing cells' DNA, subsequent generations would glow and allow the researchers to follow them.
They watched the rats' adult-born neurons for the typical six weeks, but then kept observing into the seventh. Amazingly, the seven-week-old neurons continued to exhibit growth markers, such as larger nuclei and thicker dendrites. The researchers continued their watch for 24 weeks and found the aged neurons were bigger and sported more connections than infant-born ones.
Based on the results, they think that adult-born neurons may continue to contribute to plasticity and regeneration throughout life, even if cell production winds down with age.
"Our study is exciting because it gives us a new framework for studying these cells," Snyder said. "Even if neurogenesis stops as we age, our study shows that it's still relevant because cells take so long to mature and keep growing for so long. This is really just a different way of looking at them.
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The challenge of measuring adult neurogenesis is difficult, but it's not impossible. A big part of the solution is knowing what to measure and where. While this new study was performed on rats—and therefore may be a poor predictor of what we'll see in humans—it can direct future research by showing neuroscientists where to look and what to look for.
And unlike the hard problem of consciousness, unraveling the mysteries of adult neurogenesis may have clinical applications. Better the lifecycle of neurons may reveal how neurological disorders such as Parkinson's and Alzheimer's disease emerge. There's even research linking disorders such as depression and anxiety to neurogenesis activity.
This knowledge may lead to new treatments, but if not, it could also reveal a better understanding of how our lifestyles and environments support brain health and regeneration throughout human life.
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What is human dignity? Here's a primer, told through 200 years of great essays, lectures, and novels.
- Human dignity means that each of our lives have an unimpeachable value simply because we are human, and therefore we are deserving of a baseline level of respect.
- That baseline requires more than the absence of violence, discrimination, and authoritarianism. It means giving individuals the freedom to pursue their own happiness and purpose.
- We look at incredible writings from the last 200 years that illustrate the push for human dignity in regards to slavery, equality, communism, free speech and education.
The inherent worth of all human beings<p>Human dignity is the inherent worth of each individual human being. Recognizing human dignity means respecting human beings' special value—value that sets us apart from other animals; value that is intrinsic and cannot be lost.</p> <p>Liberalism—the broad political philosophy that organizes society around liberty, justice, and equality—is rooted in the idea of human dignity. Liberalism assumes each of our lives, plans, and preferences have some unimpeachable value, not because of any objective evaluation or contribution to a greater good, but simply because they belong to a human being. We are human, and therefore deserving of a baseline level of respect. </p> <p>Because so many of us take human dignity for granted—just a fact of our humanness—it's usually only when someone's dignity is ignored or violated that we feel compelled to talk about it. </p> <p>But human dignity means more than the absence of violence, discrimination, and authoritarianism. It means giving individuals the freedom to pursue their own happiness and purpose—a freedom that can be hampered by restrictive social institutions or the tyranny of the majority. The liberal ideal of the good society is not just peaceful but also pluralistic: It is a society in which we respect others' right to think and live differently than we do.</p>
From the 19th century to today<p>With <a href="https://books.google.com/ngrams/graph?year_start=1800&year_end=2019&content=human+dignity&corpus=26&smoothing=3&direct_url=t1%3B%2Chuman%20dignity%3B%2Cc0" target="_blank" rel="noopener noreferrer">Google Books Ngram Viewer</a>, we can chart mentions of human dignity from 1800-2019.</p><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDg0ODU0My9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTY1MTUwMzE4MX0.bu0D_0uQuyNLyJjfRESNhu7twkJ5nxu8pQtfa1w3hZs/img.png?width=980" id="7ef38" class="rm-shortcode" data-rm-shortcode-id="9974c7bef3812fcb36858f325889e3c6" data-rm-shortcode-name="rebelmouse-image" />
American novelist, writer, playwright, poet, essayist and civil rights activist James Baldwin at his home in Saint-Paul-de-Vence, southern France, on November 6, 1979.
Credit: Ralph Gatti/AFP via Getty Images
The future of dignity<p>Around the world, people are still working toward the full and equal recognition of human dignity. Every year, new speeches and writings help us understand what dignity is—not only what it looks like when dignity is violated but also what it looks like when dignity is honored. In his posthumous essay, Congressman Lewis wrote, "When historians pick up their pens to write the story of the 21st century, let them say that it was your generation who laid down the heavy burdens of hate at last and that peace finally triumphed over violence, aggression and war."</p> <p>The more we talk about human dignity, the better we understand it. And the sooner we can make progress toward a shared vision of peace, freedom, and mutual respect for all. </p>
With just a few strategical tweaks, the Nazis could have won one of World War II's most decisive battles.
- The Battle of Britain is widely recognized as one of the most significant battles that occurred during World War II. It marked the first major victory of the Allied forces and shifted the tide of the war.
- Historians, however, have long debated the deciding factor in the British victory and German defeat.
- A new mathematical model took into account numerous alternative tactics that the German's could have made and found that just two tweaks stood between them and victory over Britain.
Two strategic blunders<p>Now, historians and mathematicians from York St. John University have collaborated to produce <a href="http://www-users.york.ac.uk/~nm15/bootstrapBoB%20AAMS.docx" target="_blank">a statistical model (docx download)</a> capable of calculating what the likely outcomes of the Battle of Britain would have been had the circumstances been different. </p><p>Would the German war effort have fared better had they not bombed Britain at all? What if Hitler had begun his bombing campaign earlier, even by just a few weeks? What if they had focused their targets on RAF airfields for the entire course of the battle? Using a statistical technique called weighted bootstrapping, the researchers studied these and other alternatives.</p><p>"The weighted bootstrap technique allowed us to model alternative campaigns in which the Luftwaffe prolongs or contracts the different phases of the battle and varies its targets," said co-author Dr. Jaime Wood in a <a href="https://www.york.ac.uk/news-and-events/news/2020/research/mathematicians-battle-britain-what-if-scenarios/" target="_blank">statement</a>. Based on the different strategic decisions that the German forces could have made, the researchers' model enabled them to predict the likelihood that the events of a given day of fighting would or would not occur.</p><p>"The Luftwaffe would only have been able to make the necessary bases in France available to launch an air attack on Britain in June at the earliest, so our alternative campaign brings forward the air campaign by three weeks," continued Wood. "We tested the impact of this and the other counterfactuals by varying the probabilities with which we choose individual days."</p><p>Ultimately, two strategic tweaks shifted the odds significantly towards the Germans' favor. Had the German forces started their campaign earlier in the year and had they consistently targeted RAF airfields, an Allied victory would have been extremely unlikely.</p><p>Say the odds of a British victory in the real-world Battle of Britain stood at 50-50 (there's no real way of knowing what the actual odds are, so we'll just have to select an arbitrary figure). If this were the case, changing the start date of the campaign and focusing only on airfields would have reduced British chances at victory to just 10 percent. Even if a British victory stood at 98 percent, these changes would have cut them down to just 34 percent.</p>
A tool for understanding history<p>This technique, said co-author Niall Mackay, "demonstrates just how finely-balanced the outcomes of some of the biggest moments of history were. Even when we use the actual days' events of the battle, make a small change of timing or emphasis to the arrangement of those days and things might have turned out very differently."</p><p>The researchers also claimed that their technique could be applied to other uncertain historical events. "Weighted bootstrapping can provide a natural and intuitive tool for historians to investigate unrealized possibilities, informing historical controversies and debates," said Mackay.</p><p>Using this technique, researchers can evaluate other what-ifs and gain insight into how differently influential events could have turned out if only the slightest things had changed. For now, at least, we can all be thankful that Hitler underestimated Britain's grit.</p>
We’ve mapped a million previously undiscovered galaxies beyond the Milky Way. Take the virtual tour here.
See the most detailed survey of the southern sky ever carried out using radio waves.
Astronomers have mapped about a million previously undiscovered galaxies beyond the Milky Way, in the most detailed survey of the southern sky ever carried out using radio waves.
A new study shows our planet is much closer to the supermassive black hole at the galaxy's center than previously estimated.
Arrows on this map show position and velocity data for the 224 objects utilized to model the Milky Way Galaxy. The solid black lines point to the positions of the spiral arms of the Galaxy. Colors reflect groups of objects that are part of the same arm, while the background is a simulation image.
Apple sold its first iPod in 2001, and six years later it introduced the iPhone, which ushered in a new era of personal technology.