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Comment by Dr. Krishna Kumari Challa on June 17, 2023 at 10:01am

Study finds that the human brain reactivates mental representations of past events during new experiences

Neuroscience studies have showed that as mice and other rodents navigate a maze, their brain often "replays" relevant past events. This mental replaying of events, such as the route taken until reaching their current position, could help rodents create a mental map of the spatial environment, and understand their position in it.

Researchers  recently explored the possibility that the human brain also replays past events to make sense of evolving, non-spatial experiences. Their findings, published in Nature Neuroscience, confirms this hypothesis and suggests that the process through which the human brain reactivates these events might be far more complex than that observed in rodents.

Researchers tried to devise an experiment that might elicit the replay of past events as observed in rodents, but during non-spatial daily experiences. Ultimately, they decided to ask their participants to watch a movie or listen to audio recordings of a narrated story while recording their brain activity using a functional magnetic resonance imaging (fMRI) scanner.

Movies and stories simulate real world experiences, as they are composed of events that should be linked together to understand the overall narrative.

Interestingly, researchers  found that as participants were engaged in the narrative of a movie or story, representations of past events, which were needed to make sense of each present scene, were reactivated in their brain. Unlike in rodents, these reactivations appeared while the participants were watching the movie or listening to the story, rather than during periods of rest from the task.

They found that the same brain regions that replay spatial information in the rodent brain also replay narrative events in the human brain. In other words, replay, previously thought to mainly support spatial navigation, could also underlie the human ability to make sense of narratives.  

Overall, the recent work by this team of researchers suggests that while humans are trying to make sense of their present experiences, their brain may continuously reactivate relevant past events. 

Avital Hahamy et al, The human brain reactivates context-specific past information at event boundaries of naturalistic experiences, Nature Neuroscience (2023). DOI: 10.1038/s41593-023-01331-6

Comment by Dr. Krishna Kumari Challa on June 16, 2023 at 12:50pm

Endometriosis could be caused by bacteria

Endometriosis could be caused by Fusobacterium. The severely painful condition, in which tissue similar to the uterus lining grows outside the uterus, affects up to 10% of women. In a study of 155 women, the bacterium was found in around 64% of those with endometriosis a.... Experiments with Fusobacterium-infected mice showed that antibiotics could reduce the size and frequency of the lesions that are associated with the disease. A clinical trial is now under way to find out whether antibiotics could relieve some endometriosis symptoms.

https://www.science.org/doi/10.1126/scitranslmed.add1531

https://www.nature.com/articles/d41586-023-01956-4?utm_source=Natur...

Comment by Dr. Krishna Kumari Challa on June 16, 2023 at 12:36pm

Modern high dynamic range televisions create bright white regions that are over 10,000 times brighter than their darkest black, approaching the contrast levels of natural scenes.

How our eyes and brains can handle this contrast is a puzzle because tests show that the highest contrasts we humans can see at a single spatial scale is around 200:1.

Even more confusingly, the neurons connecting our eyes to our brains can only handle contrasts of about 10:1.

This new  model shows how neurons with such limited contrast bandwidth can combine their signals to allow us to see these enormous contrasts, but the information is 'compressed'—resulting in visual illusions.

The model shows how our neurons are precisely evolved to use of every bit of capacity.

"For example, some neurons are sensitive to very tiny differences in gray levels at medium-sized scales, but are easily overwhelmed by high contrasts.

"Meanwhile, neurons coding for contrasts at larger or smaller scales are much less sensitive, but can work over a much wider range of contrasts, giving deep black-and-white differences.

"Ultimately this shows how a system with a severely limited neural bandwidth and sensitivity can perceive contrasts larger than 10,000:1."

 A model of colour appearance based on efficient coding of natural images, PLoS Computational Biology (2023). DOI: 10.1371/journal.pcbi.1011117

Part 2

Comment by Dr. Krishna Kumari Challa on June 16, 2023 at 12:35pm

New research shows illusions are in the eye, not the mind's neurons

Numerous visual illusions are caused by limits in the way our eyes and visual neurons work—rather than more complex psychological processes, new research shows.

Numerous visual illusions are caused by limits in the way our eyes and visual neurons work—rather than more complex psychological processes, new research shows.

The new study suggests simple limits to neural responses—not deeper psychological processes—explain these illusions.

Our eyes send messages to the brain by making neurons fire faster or slower. However, there's a limit to how quickly they can fire, and previous research hasn't considered how the limit might affect the ways we see color.

The model combines this "limited bandwidth" with information on how humans perceive patterns at different scales, together with an assumption that our vision performs best when we are looking at natural scenes.

The model was developed by researchers from the Universities of Exeter and Sussex to predict how animals see color, but it was also found to correctly predict many visual illusions seen by humans.

Part 1

Comment by Dr. Krishna Kumari Challa on June 16, 2023 at 12:19pm

Right-handed building blocks of life

Scientific research may have solved the puzzle of how life became molecularly right-handed. In the paper, "Origin of biological homochirality by crystallization of an RNA precursor on a magnetic surface," published in Science Advances, the researchers explain how it all might have started with the right kind of rocks.

Molecules can be left-handed, right-handed or both. RNA and the sugars that makeup DNA are right-handed molecules. Nobody knows why or if there is a reason beyond chance that life started right-handed.

As an analogy, human hands can be left or right, and they are mirror images of each other, which means that they cannot be superimposed without one facing the wrong way. Molecules can have similar structural symmetry.

In much the same way that right-handed people have difficulty with left-handed scissors, or left-handed guitar players need to reverse strings and play the instrument the other way round, molecules do not interact the same way when they are left or right-handed. Once started, it makes sense that the building blocks of life should continue with the same handedness.

One intriguing idea is that cosmic rays with left-handed spin destroyed left-handed DNA precursors just as life started on Earth.

Ribo-amino oxazoline (RAO) is a crucial RNA precursor for two of RNA's nucleotides, cytosine and uracil. RAO also happens to form a crystalline structure that can be either right-handed or left-handed that, once the crystal starts forming, right or left, only binds with other molecules of the same handedness.

By placing RAO on magnetite (Fe₃O₄) surfaces, researchers could achieve 100% handedness of RAO crystallization, either left or right, depending on the spin-exchange interaction and degree of spin alignment (magnetization) at the active surface.

Earth's most abundant natural magnetic mineral, magnetite, would have had plenty of interaction opportunities with RAO in primordial times. However, the researchers say the effect is not likely to occur in particle solution contact like mud but rather on sedimentary rock surfaces.

Even with the current findings possibly unlocking two of the four RNA nucleotide components, two more are still missing. So far, The origin story finds that common, naturally occurring components at room temperatures can start the process. If the next two are found to have similar requirements, it would indicate that life on any Earth-like planet in the universe could have started just as easily.

S. Furkan Ozturk et al, Origin of biological homochirality by crystallization of an RNA precursor on a magnetic surface, Science Advances (2023). DOI: 10.1126/sciadv.adg8274

S. Furkan Ozturk et al, Chirality-Induced Magnetization of Magnetite by an RNA Precursor, arXiv (2023). DOI: 10.48550/arxiv.2304.09095

Comment by Dr. Krishna Kumari Challa on June 16, 2023 at 11:01am

Seeing Dead Flies Makes Other Flies Die Faster

There might be a weird benefit to leaving dead flies where they fall .

Research has shown that when fruit flies of the species Drosophila melanogaster are exposed to the carcasses of their dead friends, their lifespan shrinks in a significant and measurable way.

They start acting withdrawn, lose body fat, and their aging accelerates to the point that they die sooner than fruit flies that don't see their dead buddies just lying where they fall like some macabre fruit fly graveyard.

And now scientists have a better idea about why this happens. Two neuron types receptive to the neurotransmitter serotonin become activated when fruit flies perceive dead comrades, and this increased activity accelerates the flies' aging process.

Scientists have seen similar effects in other animals: necrophoresis, or the removal of dead conspecifics, in eusocial insects; vocalization and corpse inspection in elephants; or an increase in levels of regulatory hormones called glucocorticoids in nonhuman primates.

https://journals.plos.org/plosbiology/article?id=10.1371/journal.pb...

Comment by Dr. Krishna Kumari Challa on June 16, 2023 at 9:00am

To form the vesicles and to get the nanostructures inside these vesicles, the team used an established method, placing the nanostructures in a solution of water and sugar (sucrose) and adding this to a layer of oil and lipids and another layer of glucose.

Spinning (centrifuging) this combination of substances resulted in droplets of oil with a membrane composed of a double layer of lipids, mimicking the membrane that separates cells from the outside world, with the nanostructures migrating inside these droplets.

Nishkantha Arulkumaran et al, Creating complex protocells and prototissues using simple DNA building blocks, Nature Communications (2023). DOI: 10.1038/s41467-023-36875-5

Part 2

Comment by Dr. Krishna Kumari Challa on June 16, 2023 at 9:00am

Researchers  artificially re-creates cell 'skeletons' using strands of DNA

 

 The tiny tubes and thread-like structures that give cells their shape and help determine their function have been artificially re-created using strands of DNA in a study by researchers.

The research, published in Nature Communications, represents a key step toward synthetic "smart cells" that could be used to sense diseases, deliver drugs or repair damaged cells inside the body.

Cells, about a thousandth of a millimeter in size, are the fundamental units of all life. They contain "skeletons" made of proteins that fulfill a number of functions, such as providing structural support, helping the cell move around, and transporting materials within the cell.

Re-creating these tubes and threads using proteins is challenging, so the researchers used strands of DNA as building blocks, and were able to precisely customize the structures' dimensions (from about 20 to 400 nanometers thick) and stiffness (from flexible to ultra-rigid).

These tubes and threads were integrated inside cell-like sacs as well as coated on to the sacs' exterior—functioning as a cytoskeleton (inside the cell) or exoskeleton (outside the cell). Most bacteria have what can be described as an exoskeleton, whereas plants, animals and other multicellular organisms have a cytoskeleton.

The tubes and threads were found to stabilize the sacs (vesicles), reducing the chance of them rupturing, in a similar way to how these skeletal structures work in real cells.

The research team was also able to control the exact location of the tubes and fibers in real-time while they were inside the vesicles by attaching magnetic nanoparticles to the structures using an external magnet.

 This work can help to unlock future smart cells able to sense diseases, repair damaged cells by fusing with them, and deliver drugs in a more targeted way—for instance, by carrying a drug or antibiotic and releasing it exactly where it is needed in the body.

This initial study gave promising signs that these protocells may have limited toxicity for humans and the next step is to move from the laboratory to animals to investigate further how these protocells interact with living tissue.

Researchers need to ensure they are stable in the body and able to circulate the blood stream—then we can adapt them to target cancers or pathogenic bacteria.

In addition, the researchers showed how their protocells could combine to form something analogous to living tissue. They placed the protocells in a solution of water and sugar. The cells sank (as they were heavier than the solution) and the evaporation of the water induced a swirling current that pushed the cells together. The team were able to bind these cells more tightly together by placing nanotubes or fibers on the exterior of the cells (giving the cells a "hairy" appearance). This caused the cells to lose their spherical shape and form a honeycomb pattern.

 

The researchers created the tubes and threads by placing strands of DNA in a solution of magnesium chloride, which is heated and then cooled at a fixed rate of half a degree a minute. This triggered the DNA to self-assemble into an ordered structure. By varying the magnesium concentration of the solution, the researchers were able to determine the dimensions and stiffness of the structure.

Part 1

Comment by Dr. Krishna Kumari Challa on June 14, 2023 at 11:38am

How cells kill themselves

Comment by Dr. Krishna Kumari Challa on June 14, 2023 at 10:25am

 How microplastics stick around in human airways

Research shows humans might inhale about 16.2 bits of microplastic every hour, which is equivalent to a credit card over an entire week. And these microplastics—tiny debris in the environment generated from the degradation of plastic products—usually contain toxic pollutants and chemicals.

Inhaled microplastics can pose serious health risks, so understanding how they travel in the respiratory system is essential for prevention and treatment of respiratory diseases.

Researchers  explored the movement of microplastics with different shapes (spherical, tetrahedral, and cylindrical) and sizes (1.6, 2.56, and 5.56 microns) and under slow and fast breathing conditions.

Microplastics tended to collect in hot spots in the nasal cavity and oropharynx, or back of the throat.

The complicated and highly asymmetric anatomical shape of the airway and complex flow behavior in the nasal cavity and oropharynx causes the microplastics to deviate from the flow pathline and deposit in those areas.

The flow speed, particle inertia, and asymmetric anatomy influence the overall deposition and increase the deposition concentration in nasal cavities and the oropharynx area.

Breathing conditions and microplastic size influenced the overall microplastic deposition rate in airways. An increased flow rate led to less deposition, and the largest (5.56 micron) microplastics were deposited in the airways more often than their smaller counterparts.

This study emphasizes the need for greater awareness of the presence and potential health impacts of microplastics in the air we breathe.

How microplastics are transported and deposited in realistic upper airways, Physics of Fluids (2023). DOI: 10.1063/5.0150703

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