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Neuroscientists find memory cells that help us interpret new situations
Neurons that store abstract representations of past experiences are activated when a new, similar event takes place.
However, your brain knows that you have had similar experiences — perusing a menu, ordering appetizers, and splurging on dessert are all things that you have probably done when dining out.
MIT neuroscientists have now identified populations of cells that encode each of these distinctive segments of an overall experience. These chunks of memory, stored in the hippocampus, are activated whenever a similar type of experience takes place, and are distinct from the neural code that stores detailed memories of a specific location.
The researchers believe that this kind of "event code," which they discovered in a study of mice, may help the brain interpret novel situations and learn new information by using the same cells to represent similar experiences.
"When you encounter something new, there are some really new and notable stimuli, but you already know quite a bit about that particular experience, because it's a similar kind of experience to what you have already had before," says Susumu Tonegawa, a professor of biology and neuroscience at the RIKEN-MIT Laboratory of Neural Circuit Genetics at MIT's Picower Institute for Learning and Memory.
Tonegawa is the senior author of the study, which appears today in Nature Neuroscience. Chen Sun, an MIT graduate student, is the lead author of the paper. New York University graduate student Wannan Yang and Picower Institute technical associate Jared Martin are also authors of the paper.
It is well-established that certain cells in the brain's hippocampus are specialized to store memories of specific locations. Research in mice has shown that within the hippocampus, neurons called place cells fire when the animals are in a specific location, or even if they are dreaming about that location.
In the new study, the MIT team wanted to investigate whether the hippocampus also stores representations of more abstract elements of a memory. That is, instead of firing whenever you enter a particular restaurant, such cells might encode "dessert," no matter where you're eating it.
To test this hypothesis, the researchers measured activity in neurons of the CA1 region of the mouse hippocampus as the mice repeatedly ran a four-lap maze. At the end of every fourth lap, the mice were given a reward. As expected, the researchers found place cells that lit up when the mice reached certain points along the track. However, the researchers also found sets of cells that were active during one of the four laps, but not the others. About 30 percent of the neurons in CA1 appeared to be involved in creating this "event code."
"This gave us the initial inkling that besides a code for space, cells in the hippocampus also care about this discrete chunk of experience called lap 1, or this discrete chunk of experience called lap 2, or lap 3, or lap 4," Sun says.
To further explore this idea, the researchers trained mice to run a square maze on day 1 and then a circular maze on day 2, in which they also received a reward after every fourth lap. They found that the place cells changed their activity, reflecting the new environment. However, the same sets of lap-specific cells were activated during each of the four laps, regardless of the shape of the track. The lap-encoding cells' activity also remained consistent when laps were randomly shortened or lengthened.
"Even in the new spatial locations, cells still maintain their coding for the lap number, suggesting that cells that were coding for a square lap 1 have now been transferred to code for a circular lap 1," Sun says.
The researchers also showed that if they used optogenetics to inhibit sensory input from a part of the brain called the medial entorhinal cortex (MEC), lap-encoding did not occur. They are now investigating what kind of input the MEC region provides to help the hippocampus create memories consisting of chunks of an experience.
Two distinct codes
These findings suggest that, indeed, every time you eat dinner, similar memory cells are activated, no matter where or what you're eating. The researchers theorize that the hippocampus contains "two mutually and independently manipulatable codes," Sun says. One encodes continuous changes in location, time, and sensory input, while the other organizes an overall experience into smaller chunks that fit into known categories such as appetizer and dessert.
"We believe that both types of hippocampal codes are useful, and both are important," Tonegawa says. "If we want to remember all the details of what happened in a specific experience, moment-to-moment changes that occurred, then the continuous monitoring is effective. But on the other hand, when we have a longer experience, if you put it into chunks, and remember the abstract order of the abstract chunks, that's more effective than monitoring this long process of continuous changes."
The new MIT results "significantly advance our knowledge about the function of the hippocampus," says Gyorgy Buzsaki, a professor of neuroscience at New York University School of Medicine, who was not part of the research team.
"These findings are significant because they are telling us that the hippocampus does a lot more than just 'representing' space or integrating paths into a continuous long journey," Buzsaki says. "From these remarkable results Tonegawa and colleagues conclude that they discovered an 'event code,' dedicated to organizing experience by events, and that this code is independent of spatial and time representations, that is, jobs also attributed to the hippocampus."
Tonegawa and Sun believe that networks of cells that encode chunks of experiences may also be useful for a type of learning called transfer learning, which allows you to apply knowledge you already have to help you interpret new experiences or learn new things. Tonegawa's lab is now working on trying to find cell populations that might encode these specific pieces of knowledge.
The research was funded by the RIKEN Center for Brain Science, the Howard Hughes Medical Institute, and the JPB Foundation.
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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>
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- The debate over whether or not humans have free will is centuries old and ongoing. While studies have confirmed that our brains perform many tasks without conscious effort, there remains the question of how much we control and when it matters.
- According to Dr. Uri Maoz, it comes down to what your definition of free will is and to learning more about how we make decisions versus when it is ok for our brain to subconsciously control our actions and movements.
- "If we understand the interplay between conscious and unconscious," says Maoz, "it might help us realize what we can control and what we can't."
Puerto Rico's iconic telescope facilitated important scientific discoveries while inspiring young scientists and the public imagination.
- The Arecibo Observatory's main telescope collapsed on Tuesday morning.
- Although officials had been planning to demolish the telescope, the accident marked an unceremonious end to a beloved astronomical tool.
- The Arecibo radio telescope has facilitated many discoveries in astronomy, including the mapping of near-Earth asteroids and the detection of exoplanets.
Bradley Rivera via twitter.com<p>In 1963, the concave dish was built into a natural sinkhole on the northern coast of Puerto Rico. The location was <a href="https://www.space.com/20984-arecibo-observatory.html" target="_blank">picked because it was near the equator,</a> providing scientists a clear view of planets passing overhead, and also of the ionosphere, which is the uniquely reactive layer of Earth's upper atmosphere where the northern lights form.</p><p>Since its construction, scientists have used the Arecibo telescope to map near-Earth asteroids, detect gravitational waves, study pulsars, detect exoplanets and <a href="https://www.seti.org/goodbye-arecibo" target="_blank">search for alien civilizations</a>, among other projects. Here's a brief look at some of the discoveries and accomplishments made using the Arecibo telescope:</p><ul><li>1964: Astronomer <a href="https://en.wikipedia.org/wiki/Gordon_Pettengill" target="_blank" rel="noopener noreferrer">Gordon Pettengill</a> discovers that Mercury's rotation period is 59 days, significantly shorter than the previous prediction of 88 days.</li><li>1974: Physicists Russell Alan Hulse and Joseph Hooton Taylor Jr. discovers the first binary pulsar, for which they won a Nobel Prize in Physics.</li><li>1974: Scientists use the telescope to transmit the "Arecibo message" to <a href="https://en.wikipedia.org/wiki/Great_Globular_Cluster_in_Hercules" target="_blank" rel="noopener noreferrer">globular star cluster M13</a>. The message, when translated into image form, contains basic information about humanity and human knowledge: the numbers one to 10, a map of our solar system, an illustration of a human being, and the atomic numbers of certain elements.</li><li>1989: Scientists use the telescope to image an asteroid for the first time.</li><li>1992: Astronomers Alex Wolszczan and Dale Frail become the first to discover exoplanets.</li></ul>
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