Researchers discover brain cells that express sense of time within experiences memories

first_img Source:https://www.ntnu.edu/web/kavli/news Reviewed by James Ives, M.Psych. (Editor)Aug 30 2018Location: Address Opening Hours: Ticket price: Broadcast content type: Broadcast starts: Broadcast duration: Publication title: Author: Publication type: Publication date: Number of pages: ISBN number: Price: Researchers at the Kavli Institute for Systems Neuroscience in Trondheim, Norway have discovered a network of brain cells that express our sense of timewithin experiences and memories.”This network provides timestamps to events and keeps track of the order of events within an experience,”says Professor Edvard Moser, director of the institute, based at the Norwegian University of Science and Technology (NTNU). Thearea of the brain where time is experienced is located right next to the area that codes for space.Telling timeClocks are devices created by humans to measure time. By social contract, we agree to coordinate our own activities according to clock time. Nevertheless, your brain does not perceive the duration in time with the standardized units of minutes and hours on your wristwatch. The signature of time in our experiences and memories belongs to a different kind of temporality altogether.Over the course of evolution, living organisms including humans have developed multiple biological clocks to help us keep track of time. What separates the brain’s various timekeepers is not only the scale of time that is measured, but also the phenomena the neural clocks are tuned to. Some timekeepers are set by external processes, like the circadian clock that is tuned to the rise and fall of daylight. This clock helps organisms adapt to the rhythms of a day.Other timekeepers are setby phenomena of more intrinsic origins, like the hippocampal time cells that form a domino-like chain signal that tracks time spans up to 10 seconds precisely. Today we know a great deal about the brain’s mechanisms for measuring small timescales like seconds. Little is known, however, about the timescale the brain uses to record our experiences and memories, which can last anywhere from seconds to minutes to hours.A neural clock for experienced timeA neural clock that keeps track of time during experiences is precisely what AlbertTsao and his colleagues at NTNU’sKavli Institutebelieve they have discovered. By recording from a population of brain cells the researchers identified a strong time-coding signal deep inside the brain.”Our study reveals how the brain makes sense of time as an event is experienced,” says Tsao. “The network does not explicitly encode time. What we measure is rather a subjective time derived from the ongoing flow of experience.”The neural clock operates by organizing the flow of our experiences into an orderly sequence of events. This activity gives rise to the brain’s clock for subjective time. Experience, and the succession of events within experience, are thus the substance of which subjective time is generated and measured by the brain.Time, space and memory in the brain”Today, we have a fairly good understanding of the way our brains process space whereas our knowledge of time is less coherent,”Professor Moser says.”Space in the brain is relatively easy to investigate. It consists of specialized cell types that are dedicated to specific functions. Together they constitute the nuts and bolts of the system,”he says.In 2005, May-Britt and Edvard Moser discovered grid cells which map our environment at different scales by dividing space into hexagonal units. In 2014, The Mosers shared the Nobel Prize in Physiology or Medicine with their colleague and mentor John O’Keefe at University College London for their discoveries of cells that constitute the brain’s positioning system.In 2007, inspired by the Mosers’ discovery of spatially coding grid cells, then-Kavli Institute PhD candidate Albert Tsao set out to crack the code of what was happening in the enigmatic lateral entorhinal cortex (LEC). This area of the brain is right next to the medial entorhinal cortex (MEC), where his supervisors, the Mosers, had discovered grid cells.Related StoriesNew therapy shows promise in preventing brain damage after traumatic brain injuryDon’t Miss the Blood-Brain Barrier Drug Delivery (B3DD) Summit this AugustPosterior parietal cortex plays crucial role in making decisions, research shows”I was hoping to find a similar key operating cell that would reveal the functional identity of this neural network,”Tsao says. The task proved to be a time-consuming project.”There didn’t seem to be a pattern to the activity of these cells. The signal changed all the time,” says Professor Moser.It was only in the last couple of years that the researchers began to suspect that the signal was indeed changingwithtime. Suddenly the recoded data started to make sense.”Time is a non-equilibrial process. It is always unique and changing,” Professor Moser says.”If this network was indeed coding for time, the signal would have to changewithtime in order to record experiences as unique memories.”Technological advancementsThe Mosers needed only to decode the signal of one single grid cell to discover how space is encoded in thein the medial entorhinal cortex. Decoding time in the lateral entorhinal cortex proved to be a more complex task. It was only when looking at activity from hundreds of cells that Tsao and his colleagues were able to see that the signal encoded time.”The activity in these neural networks is so distributed that the mechanism itself probably lies in the structure of connectivity within the networks. The fact that it can be shaped into various unique patterns implies a high level of plasticity,” Professor Moser says. “I believe distributed networks and the combination of structures of activity may deserve more attention in the future. With this work, we have found an area with activity so strongly relating to the time of an event or experience, it may open up a whole new research field.”The Shape of TimeThe structure of time has long been a disputed topic by philosophers and physicists alike. What can the newly discovered brain’s mechanism for episodic time tell us about how we perceive time? Is our perception of time linear resembling a flowing river, or cyclical like a wheel or a helix? Data from the Kavli study suggest both are correct, and that the signal in the time-coding network can take on many forms depending on the experience.In 2016, PhD candidate Jørgen Sugar joined the Kavli project to perform a new set of experiments that would test the hypothesis that the LEC network coded for episodic time. In one experiment a rat was introduced to a wide range of experiences and options for action. It was free to run around, investigate and chase bits of chocolate while visiting a series of open space environments.”The uniqueness of the time signal during this experiment suggests that the rat had a very good record of time and temporal sequence of events throughout the two hours the experiment lasted,” Sugar says. “We were able to use the signal from the time-coding network to track exactly when in the experiment various events had occurred.”In the second experiment, the task was more structured with a narrower range of experiences and options for action. The rat was trained to chase after bits of chocolate while turning left or right in a figure-eightmaze.”With this activity, we saw the time-coding signal change character from unique sequences in time to a repetitive and partly overlapping pattern,”Tsao says. “On the other hand, the time signal became more precise and predictable during the repetitive task. The data suggest that the rat had a refined understanding of temporality during each lap, but a poor understanding of time from lap to lap and from the start to end throughout the experiment.”Professor Moser says the study shows that by changing the activities you engage in, the content of your experience, you can actually change the course of the timesignal in the LEC and thus the way you perceive time.last_img read more

Placenta Harbors Bacteria May Impact Fetal Health

Sign up for our daily newsletter Get more great content like this delivered right to you! Country Researchers have discovered a small community of bacteria living in a most unlikely place: the placenta, the organ that nourishes a developing fetus through the umbilical cord. The finding overturns the conventional wisdom that the placenta is sterile. The study also suggests that these microbes may come from the mouth, affirming that good oral hygiene may be important for a healthy pregnancy.The placenta is a pancake-shaped mass of tissue on the side of the uterus that provides oxygen, food, and waste removal to a fetus. Medical experts have long assumed that any bacteria found in the organ must have been picked up when it passed through the vagina after delivery. But more recently, researchers have realized that a baby has a community of bacteria in its gut when it is born. And these bacteria don’t match those in the vagina, suggesting some other source, such as the placenta, says fetal medicine specialist Kjersti Aagaard of Baylor College of Medicine in Houston, Texas.Aagaard and co-workers are collaborators on the U.S. Human Microbiome Project, which is studying microbiomes—communities of bacteria, fungi, and viruses—that live in various places on and in our bodies. They looked for a placental microbiome by analyzing carefully collected placentas from 320 pregnancies. The researchers extracted DNA from the placentas and sequenced it for snippets and entire bacterial genomes in order to identify and quantify microbial species and the genes they carried. This analysis revealed low levels of a diverse set of bacteria, mostly nondisease causing strains of Escherichia coli, which dominate our intestinal tracts, but also others from five broad groups, or phyla. Most were benign species known to provide services such as metabolizing vitamins. 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Required fields are indicated by an asterisk (*) Surprisingly, the mix of bacteria in the placenta looked more like the microbiome in an adult human’s mouth than the vaginal, skin, gut, or other body microbiomes, Aagaard’s team reports today in Science Translational Medicine. The researchers think the microbes may get to the placenta from the mother’s mouth through her bloodstream, perhaps when she brushes her teeth and dislodges them into the blood. That possibility is intriguing, because there’s a well-known correlation between gum disease and preterm birth. Indeed, the array of bacteria in the placenta differed in women who gave birth early, before 37 weeks.“This reemphasizes the importance of oral health” during pregnancy, Aagaard says. In fact, women may need to pay attention to their teeth even before they may become pregnant, because the placenta develops early in pregnancy, she says. That may be a challenge for low-income women who can’t afford dental care, Aagaard adds. The team also found a correlation between the composition of the placental microbiome and urinary tract infections, which suggests that such illnesses or antibiotics taken to treat them could alter the microbiome in unhealthy ways.“This study is the first to suggest that all placentas contain a small amount of bacteria,” says perinatal researcher Roberto Romero of the National Institute of Child Health and Human Development campus in Detroit, Michigan. “These bacteria may live there and have a specific purpose,” such as seeding the fetus’s intestinal microbiome or building its immune system, adds biologist Indira Mysorekar of Washington University in St. Louis, who has reported finding bacteria inside certain placental cells.However, Romero and others caution that it’s too soon to say exactly how the placental microbiome got there and what it’s doing. The bacteria could have been in the uterus before pregnancy and evolved to resemble those in the mouth, Mysorekar says. Despite these unknowns, says microbiologist Seth Bordenstein of Vanderbilt University in Nashville, the discovery of a placental microbiome “continues to build the snowball that no tissue in the human body is sterile.” read more