Childhood memories are not gone, we just can’t read them｜Tech Weekly

Compiled by Zhou Shuyi and Pingsheng

Why do animals mate in a "step-by-step" manner? Research reveals brain signaling mechanism

In Kafka's "The Castle", K and Frieda make love for a long time on the floor of a tavern. He feels that he has "lost his way" and entered a "strange country farther than anywhere else", which is the novel's lyrical expression of sex. From a scientific perspective, what exactly happens in the brain during a series of behaviors from erection, penis insertion into the vagina, to ejaculation? A new study explored the brain activity of male rats during sexual behavior and found that the complex changes of two chemicals responsible for producing pleasure - dopamine and acetylcholine - control the sequence of sexual behavior. The relevant paper was published in Neuron on March 20.

"Sexual behavior is a complex series of events," said Qinghua Liu, a researcher at the Institute of Life Sciences in Beijing and the corresponding author of the paper. "This study reveals how different chemicals work together in the brain to regulate the transitions between different stages of male sexual behavior."

The nucleus accumbens is an area of ​​the brain involved in reward function that responds to dopamine, a chemical often associated with pleasure. The research team used fiber photometry to monitor the nucleus accumbens in live male mice in real time with high temporal resolution. The optical fiber lights up when the brain releases dopamine and acetylcholine, a neurotransmitter known to regulate dopamine.

The results showed that before erection, the mouse brain began to release acetylcholine rhythmically, and about 6 seconds later, the brain also began to release dopamine. During the insertion of the penis, the release of acetylcholine and dopamine fluctuated rhythmically with the mouse's movements. In the transition from insertion to ejaculation, the release of dopamine slowed down significantly and then rose rapidly. The study also found that the concentration of dopamine plays an important role. During intercourse, the activity of nerve cells expressing the two main dopamine receptors D2R and D1R is lower than normal. If D1R is artificially activated at this time, the mouse will immediately return to the erection stage. If D2R is activated, the mouse will completely stop sexual activity.

"We have revealed the precise mechanism of dopamine signaling that ensures sexual behavior proceeds in the correct order." The researchers pointed out that although the sexual behavior of mice and humans is different, the brain areas and neurotransmitter systems involved in sexual function may be similar. They believe that this study may provide new clues for the treatment of sexual dysfunction such as premature ejaculation.

Related papers:
http://dx.doi.org/10.1016/j.neuron.2025.01.032

The clearest baby photo of the universe yet

At the annual meeting of the American Physical Society on March 20, an international research team announced that they had used the Atacama Cosmology Telescope (ACT) to take the clearest images of the universe about 380,000 years after its birth (the earliest cosmic era that humans have been able to observe so far). The universe at this time is equivalent to its "infancy", and these images are equivalent to "baby photos" of the universe. The relevant papers have been submitted to the Journal of Cosmology and Astroparticle Physics.

New images of the infant universe show the intensity and polarization of the earliest light, revealing the formation of ancient, condensing clouds of hydrogen and helium that later grew into the first galaxies and stars.

The cosmic microwave background radiation represents the first stage in the history of the universe that people can see - the infant stage. The resolution of these cosmic microwave background radiation images is five times that of the Planck telescope more than a decade ago, and for the first time clearly reveals the movement of hydrogen and helium in the early universe. Susan Staggs, director of the ACT project, said that they can not only see light and darkness, but also track the movement of matter through the polarization of light, just like inferring the existence of the moon through tides, and recreating the distribution of gravity in different regions of the universe.

During the first few hundred thousand years after the Big Bang, the primordial plasma that filled the universe was so hot that light could not propagate freely, making the universe effectively opaque.

Research has confirmed that the radius of the observable universe is about 50 billion light years, and the total mass is equivalent to 1900 "ζ-suns" (1 ζ=10^21). Of this, dark matter accounts for 26% (500 ζ-suns), dark energy accounts for 68% (1300 ζ-suns), and ordinary matter accounts for only 6% (100 ζ-suns). In addition, the mass of tiny neutrino particles is at most equivalent to 4 ζ-suns.

Atacama Cosmology Telescope | Debra Kellner

Thibaud-Louis, one of the main authors of the paper and a professor at Paris-Saclay University in France, pointed out that almost all the helium in the universe was formed within 3 minutes after the Big Bang, while the elements that make up the human body, mainly carbon, as well as oxygen, nitrogen, iron, and even trace amounts of gold, were formed later in stars. They are just embellishments in this cosmic "hodgepodge".

The new data confirms that the age of the universe is 13.8 billion years, with an uncertainty of 0.1%. The team also verified the Hubble constant, which measures the rate at which the universe is expanding. The results show that its value is between 67-68 km/(s⋅Mpc).

Research has proven that the current standard model of cosmology is still very reliable. (Science and Technology Daily)

VR tool helps overcome public speaking anxiety

Researchers from the University of Cambridge have launched a virtual reality (VR) online platform that allows users to practice speaking in front of thousands of virtual audiences to help overcome nervousness in real-life scenarios.

The platform is based on "exposure therapy" - facing fear can relieve fear, combined with breathing and eye movement training to help calm the heart rate and inhibit fear response. The platform integrates different scenarios such as learning materials, work reports and job interviews. From a few listeners yawning and scratching their heads in the classroom to a crowded stadium with tens of thousands of people, users can choose a variety of virtual environments for practice, and can also add distractions such as flashing lights and noise.

"The aim is to give users greater resilience and adaptability," said Chris Macdonald, who runs the platform and is based at the University of Cambridge's Immersive Technology Lab. "It's like psychological weight training," he added, hoping that people will be able to handle smaller audiences with ease.

Users can practice speaking in a variety of virtual reality environments | Lucy Cavendish

The researchers tested the platform with 29 Chinese teenagers. They used the VR system and received simple breathing training, alternating between practicing for 30 minutes and then giving a one-minute speech in English to 34 real-life audiences. Through training, the proportion of participants who felt anxious about public speaking dropped from 65% to 20%, and the proportion of participants who felt confident increased from 31% to 79%. In another unpublished study, similar benefits were observed in 18 students who were trained without having to give live speeches.

Matteo Cella, a psychologist and director of the Virtual Reality Laboratory at King's College London, questioned that the current research is limited and not comprehensive enough, and that a strong randomized controlled trial is needed to evaluate the effectiveness of the training. He warned that overexposure could backfire and increase people's avoidance of public speaking. Kim Smallman of Cardiff University also said that further research is needed to evaluate its effectiveness and safety risks.

Related papers:
https://doi.org/10.3389/frvir.2024.1506938

Platform address:
https://www.virtualrealitypublicspeaking.com/

The memories of childhood are not gone, we just can’t read them

Do you remember anything before the age of 3? In fact, we usually cannot remember the first 3 years of our lives. This phenomenon was named "infantile amnesia" by Freud. The traditional view is that this is because the infant brain, especially the hippocampus (a key area in the brain for storing memory), is not fully developed and therefore cannot encode memories.

A study published in Science on March 20 overturned the above view and found that babies can form memories at the age of 1, which shows that forgetting in infancy is likely because the memory is difficult to read rather than not formed. "A very cool possibility is that these memories are likely to still exist in adulthood, but we just can't retrieve them." Tristan Yates, a neuroscientist at Columbia University and co-author of the paper, said.

Researchers conduct fMRI scans on young children's brains｜160/90

In the new study, researchers asked 26 infants aged 4 to 25 months to watch photos of strangers' faces, objects or scenes. Each photo was presented for 2 seconds, and then they watched the new and old photos again about a minute later. During this period, functional magnetic resonance imaging (fMRI) was used to monitor the activity of the hippocampus in the infants' brains. When seeing familiar old photos, the infants spent more time looking at them, indicating that they remembered the relevant images. The results showed that the more active the hippocampus was when the infants first viewed the image, the longer they looked at the image again, indicating that even if the hippocampus is not yet fully developed, it can still perform a certain degree of episodic memory encoding. The above phenomenon is particularly evident in infants over 12 months old. In other words, one-year-old babies already have the ability to encode memories.

Therefore, forgetting childhood experiences as an adult seems to be a "reading" problem. The researchers said this may be because over time, "the way memories are initially stored and the way the brain tries to retrieve them no longer match each other." The growth process from infants to adults is completely different, "even if it's just from crawling to walking, the way we see the world will become completely different."

Animal experiments also support the above view that childhood memories can remain in the brain for many years. In a 2016 study, neuroscientists successfully activated neurons that encoded childhood memories in adult rats using optogenetics, indicating that these memories still exist.

French philosopher Bergson believed that "memory is the intersection of thought and matter" and is "the surviving image of the past" from which we can glimpse the "continuous self" - our childhood memories may not have dissipated, but when we look back many years later, those original footprints have long been buried deep in the snow.

Related papers:
https://www.science.org/doi/10.1126/science.adt7570

Is dark energy getting weaker?

At the annual meeting of the American Physical Society on March 20, the Dark Energy Spectroscopic Survey (DESI) collaboration released the latest research results on dark energy and simultaneously released the spectral data of the first year of the project. Using the data collected in the first three years and combining it with other survey information, they found that over the past 4.5 billion years, the effect of dark energy on the expansion of the universe may have weakened over time. This discovery suggests that there may be new physics beyond the current standard model of the universe.

DESI is an international dark energy experiment involving more than 70 institutions around the world, led by the U.S. Department of Energy's Lawrence Berkeley National Laboratory. The project uses the 4-meter Mayall Telescope at Kitt Peak National Optical Observatory in the United States to collect light from distant galaxies through 5,000 optical fibers. Researchers can use this to determine the degree to which the light is "redshifted" due to the expansion of the universe, thereby mapping the universe in three dimensions and reconstructing its detailed growth history.

A slice of the universe map observed by DESI shows the distribution of celestial bodies within a distance range of 11 billion light-years from Earth. The slice contains four types of extragalactic celestial targets: bright galaxies (yellow), bright red galaxies (orange), emission line galaxies (blue) and quasars (green). | DESI International Collaboration

Dark energy is an unknown component that drives the accelerated expansion of the universe. Its properties can be revealed through baryon acoustic oscillations (BAO), a density ripple left by sound waves from the early universe. The characteristic scale (about 500 million light years) formed by BAO in the distribution of matter can be regarded as a "standard ruler". By measuring the actual angular diameter of this scale at different redshifts, scientists can accurately calculate the historical changes in the expansion rate of the universe and then analyze the evolution of dark energy.

The DESI collaboration used the largest three-dimensional map of the universe to date (covering nearly 15 million galaxies and quasars) to track the effects of dark energy over the past 11 billion years. Researchers combined DESI data, the cosmic microwave background, supernovae, and weak gravitational lensing research results and found that the current standard model of cosmology can hardly explain all the observations, and the model of dark energy changing over time is more consistent with these data. Studies have shown that the acceleration of the expansion of the universe is now smaller than in the past, and the current energy density of dark energy is about 10% lower than it was 4.5 billion years ago. Dark energy, which is widely considered to be a "cosmological constant," may evolve over time in unexpected ways, which challenges the current standard cosmological model.

However, the evidence supporting the evolution of dark energy has not yet reached the gold standard discovery threshold of "5" in physics, and the current confidence range is between 2.8 and 4.2. As the survey progresses, the confidence may reach the gold standard, which may promote the revision of the existing standard cosmological model.

Why are night owls more likely to suffer from depression?

Simon Evans and colleagues at the University of Surrey in the UK have found that factors such as sleep and drinking may help explain why people who stay up late are at greater risk of depression. The relevant research was published in the Public Library of Science Comprehensive on March 19.

Previous studies have shown that "night owls" or people who stay up late have more depressive symptoms than those who wake up early. In this new study, Evans and his colleagues collected data from 546 college students through an online questionnaire. The data included information on students' self-reported sleep, concentration, rumination, drinking, depression and anxiety levels.

The study confirmed that "night owls" had a significantly higher risk of depression, and this association could be explained by differences in concentration, sleep quality, and alcohol consumption. On average, these evening people had poorer sleep quality, higher alcohol intake, and were less focused than morning people.

However, the researchers said the study was limited in its ability to prove cause and effect because its cross-sectional design relied on data from only one time point. In addition, the findings may not apply to age groups other than college students. Taking these factors into account, the researchers said interventions targeting mindfulness, sleep, and alcohol use have the potential to reduce the risk of depression, especially in young people.

"These findings are particularly important given the poor mental health of many young people - many young people tend to stay up late, and the results point to how interventions can be implemented to reduce their risk of depression," Evans said. (China Science Daily)

Related papers:
https://doi.org/10.1371/journal.pone.0319915

New antifungal drug kills multidrug-resistant fungi

In a study published in Nature on March 20, researchers mined and biosynthesized Mandimycin, the first polyene macrolide antifungal drug candidate with a new target, from microbial genomes. Mandimycin has the characteristics of broad-spectrum efficacy, new mechanism, and high safety, and exhibits strong antifungal activity against multidrug-resistant pathogens.

Infections caused by multi-drug resistant fungal pathogens are posing an increasing threat to human health. Bacteria have evolved antibiotics that can kill fungi, which can be used by humans to develop antifungal drugs. Studies have shown that in order to maintain a competitive advantage in the natural environment, antibiotic-producing bacteria will continuously optimize the structure of antibiotics through molecular modification to combat drug-resistant bacteria. Based on this, the researchers constructed a database of 1.78 million microbial secondary metabolite biosynthetic gene clusters, used gene mining technology to lock key biosynthetic gene clusters, and finally obtained Mandimycin, the first new polyene macrolide antibiotic targeting phospholipid molecules through combinatorial biosynthesis. Mandimycin does not bind to ergosterol on the cell membrane (a typical target of polyene macrolides), but instead binds to a variety of phospholipids on the fungal cell membrane. This means that it can effectively target fungal pathogens that have tolerated ergosterol-targeted antifungal agents (such as amphotericin B, which is widely used in clinical practice). The authors used animal infection models to test the effects of Mandimycin on a range of fungal pathogens, including multi-drug resistant Candida auris, and found that this compound was more effective than amphotericin B and had lower nephrotoxicity. However, given the potential side effects of its phospholipid targeting mechanism, the research team will next explore its toxicological mechanisms in depth and comprehensively evaluate its clinical safety and effectiveness.

Related papers:
https://www.nature.com/articles/s41586-025-08678-9

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