“Significant proportion” of world’s rural population missing from global estimates, says study

Global population datasets, crucial for decision-making by governments and institutions, may underestimate rural populations by as much as 53% to 84%, reveals an Aalto University study

Aalto University

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The map shows the location of the 307 rural areas analysed in the study. The reported populations in the graphic were found to be underestimated by between 53 and 84 percent. 

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Credit: Josias Láng-Ritter et. Al / Aalto University

Global population datasets, crucial for decision-making by governments and institutions, may underestimate rural populations by as much as 53% to 84%, reveals an Aalto University study. 

Governments, international bodies and researchers rely on global population data for resource allocation and infrastructure planning to disease epidemiology and disaster risk management. In a new study published in Nature Communications, researchers from Aalto University in Finland show the profound and systematic extent to which these datasets underestimate rural population figures worldwide. 

'For the first time, our study provides evidence that a significant proportion of the rural population may be missing from global population datasets,' says postdoctoral researcher Josias Láng-Ritter from Aalto University. 

‘We were surprised to find that the actual population living in rural areas is much higher than the global population data indicates — depending on the dataset, rural populations have been underestimated by between 53% to 84% over the period studied. The results are remarkable, as these datasets have been used in thousands of studies and extensively support decision-making, yet their accuracy has not been systematically evaluated,’ he says. 

Population censuses are root cause for biases 

Due to a lack of comprehensive reference data, previous attempts to gauge the accuracy of global population datasets have tended to focus on individual countries or urban areas.  

In their study, the Aalto University researchers compared the five most widely used global population datasets*— maps that divide the planet into evenly spaced, high-resolution grid cells with population counts based on census data — with resettlement numbers from over 300 rural dam projects in 35 countries.  

The study focused on population maps for the period 1975-2010, due to a lack of dam data from later years. Findings showed 2010 datasets had the least bias, missing between one-third (32%) to three-quarters (77%) of the rural population. Although global population datasets from subsequent years (2015 and 2020) have been taken into use, the team says there is strong reason to believe the latest data still misses part of the global population. 

‘While our study shows accuracy has somewhat improved over decades, the trend is clear:  global population datasets miss a significant portion of the rural population. With the same basic practices in place, it’s unlikely that slightly improved input data could correct for this level of bias. And even if the most recent population maps reflected reality, earlier datasets have influenced decision-making for decades and are still used to monitor change, for instance providing a distorted picture of movement over time from the countryside to urban areas,’ says Láng-Ritter. 

Population censuses, the key input for the population datasets in use, are considered to be incomplete to varying degrees across regions. Not all nations have the resources for precise data collection and rural regions can be difficult to travel to, with populations spread thinly over vast areas. 

Resettlement data from dam projects, in turn, provide multinational, independently gathered comparison points.  

'When dams are built, large areas are flooded and people need to be relocated,’ says Láng-Ritter. 'The relocated population is usually counted precisely because dam companies pay compensation to those affected. Unlike global population datasets, such local impact statements provide comprehensive, on-the-ground population counts that are not skewed by administrative boundaries. We then combined these with spatial information from satellite imagery.” 

Researchers found that the negative bias was systemic worldwide, with discrepancies particularly noticeable across datasets in China, Brazil, Australia, Poland and Colombia, where information was more readily available.  

Population data critical for planning and development 

With current estimates placing 43 percent of the world's 8.2 billion people in rural areas, the new findings have far-reaching consequences. Official population estimates published by the UN and the World Bank rely on the same national censuses that are the basis for the population maps. 

According to Láng-Ritter, the findings suggest that the needs of people living in rural areas have been under-represented in decision-making globally compared to urban areas. Inadequate demographic data may have led to insufficient resources for health care or transport in rural regions, for example.  

'In many countries, there may not be sufficient data available on a national level, so they rely on global population maps to support their decision-making: Do we need an asphalted road or a hospital? How much medicine is required in a particular area? How many people could be affected by natural disasters such as earthquakes or floods?' he says. 

The necessity of the information may affect countries and regions differently, the team acknowledges, and even with inaccuracies the datasets hold crucial insight for policy and research. 

‘For example here in Finland, the population data is nowadays very reliable even in rural regions, as we were the second country in the world to start keeping digital population records already in 1990. But especially in crisis-hit countries, the shift towards digital population registers could take years, even decades,' says Láng-Ritter. ‘To provide rural communities with equal access to services and other resources, we need to have a critical discussion about the past and future applications of these population maps.' 

* The population datasets included in the study were WorldPop, GWP, GRUMP, LandScan, and GHS-POP.  

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Journal

Nature Communications

DOI

10.1038/s41467-025-56906-7 

Article Title

Global gridded population datasets systematically underrepresent rural population

Article Publication Date

18-Mar-2025

BOTH ARE ENVIROMENTAL TOXINS

The combined use of insect repellent and sunscreen reportedly reduces UV protection

CNRS

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Histometric analysis of UVB-irradiated human skin biopsies after application of sunscreen and/or insect repellent or “combo” product. Skin samples (from the same donor) were treated with a sunscreen containing UV filters (panels d and e), or (panels c and e) a mosquito repellent containing the synthetic active ingredient IR3535, or a commercial preparation composed of a natural insect repellent and a sunscreen (f) (“combo spray”). Except in the control condition (panel a), skin biopsies were previously exposed to UVB irradiation under controlled conditions (300 mJ/cm2). Histological sections stained with saffron hematoxylin-eosin. Scale bar: 50 µM. Inset details show areas of interest with haloed nuclei (reflecting cellular damage) indicated by arrows

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Credit: © Sophie Charrasse

Conducted by CNRS researchers1, an unprecedented study on the combined use of sunscreen and an insect repellent that is among the best selling in France during summer concludes that UV2 protection decreases after application of the mixture. With the spread of tiger mosquitoes in many countries, it has become increasingly common for people to combine these two products during outdoor activities3 to protect themselves from both the sun and these pests. This is the first paper that studies the effects of such a mixture. It has just appeared in Parasites and Vectors.

In order to reproduce the real conditions to which the human epidermis is subjected as faithfully as possible, scientists have used skin biopsies4. Optimally preserved ex vivo, these samples were subjected to artificial and natural UV rays emitted by the Sun, after application of sunscreen and repellent. Thanks to a new computer tool developed by one of the partner companies of this study5, they were analyzed in the form of thin slices corresponding to the different layers of the skin. This software, a deep-learning artificial intelligence system6, made it possible to measure the stress response of skin cells to the radiation.

The analysis of these data points to a decrease in UV protection in the case of a mixture of sunscreen and insect repellent. For "mixed" products, presenting themselves as carrying both protections at the same time, the data obtained are less categorical. Further studies are needed to consolidate and extend these initial results. Many other product mixtures, including cosmetics, have never been studied as such. This new analytical method, combining the use of biopsies (more reliable than tests on in vitro cultured cells) and artificial intelligence, would now allow the examination of their effects on human health.

Notes

1 – From the Institut des Sciences de l'Évolution de Montpellier (CNRS, IRD, Université de Montpellier).

2 – UV, which stand for Ultra Violet, are rays that are invisible to the naked eye. They carry more energy than visible light ; therefore, they can cause detrimental mutations to skin cells if one is exposed to them for too long.

3 – Tiger mosquitoes originate from South East Asia. They were accidentally transported to Europe during the 1990s and 2000s. Unlike their western cousins, they are livelier at daylight, hence why they tend to sting more during the day.

4 – Sample (a skin one here) collected from a living organism.

5 – This study was conducted in partnership with two French companies : QuantaCell and EDENCOS.

6 – Deep-learning is a methodology which is used to train artificial neuron networks. They are given a very large amount of data in order to learn about a phenomenon or to spot specific patterns that they are able to identify in future data sets.

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Journal

Parasites & Vectors

DOI

10.1186/s13071-025-06712-3 

Method of Research

Observational study

Subject of Research

Human tissue samples

Article Title

Computational histology reveals that concomitant application of insect repellent with sunscreen impairs UV protection in an ex vivo human skin model

Article Publication Date

18-Mar-2025

 

Scientists map neural wiring of vocal circuits in songbirds

A new study provides the first detailed map of how sensory and motor circuits interact in the zebra finch brain, offering insights into how songbirds learn and refine their songs

eLife

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Researchers have mapped the long-range synaptic connections involved in vocal learning in zebra finches, uncovering new details about how the brain organises learned vocalisations such as birdsong. 

The study, published today as a Reviewed Preprint in eLife, is described by the editors as having fundamental significance and compelling evidence clarifying how four distinct inputs to a specific region of the brain act on three distinct cell types to facilitate the learning and production of birdsong.

Understanding how the brain integrates sensory and motor information to guide learned vocalisations is crucial for studying both birdsong and human speech. The courtship song of male zebra finches is a well-studied example of a naturally learned behaviour, and is controlled by a set of interconnected forebrain regions in the dorsal ventricular ridge (DVR) – the avian equivalent of the mammalian neocortex. Within this network, the premotor region HVC is essential for birds to both learn songs when they are young and to produce them when they are adults. Whilst the major pathways involved in guiding birdsongs have been established, the precise synaptic-level connections between different brain areas have remained difficult to establish due to technological limitations.

“Songbirds, like humans, learn their vocalisations through imitation and practice, relying on sensory feedback to refine their songs,” explains lead author Massimo Trusel, an Instructor in the Department of Neuroscience, UT Southwestern Medical Center, Texas, US. “We set out to uncover how different sensory inputs interact with HVC in the zebra finch song network to provide a framework for understanding how the brain organises learned vocal behaviour.” 

To map the synaptic connectivity of the HVC region, Trusel and colleagues used an optimised version of optogenetic circuit mapping, which allowed them to manipulate auditory and thalamic inputs from specific brain regions one-by-one, and record the activity of the HVC circuit. They could then trace how sensory and motor information converges on the circuits responsible for song production. They examined how inputs from four main sensory pathways interact with three key HVC cell types: HVC-RA neurons, which send signals to brain areas controlling movement for singing; HVC-AV neurons, which send motor signals to auditory areas involved in processing auditory feedback; and HVC-X neurons, which connect to the basal ganglia, a region that helps with learning and adjusting song patterns.

Their findings suggest HVC is organised into highly structured neural modules that contain both projection neurons and inhibitory interneurons, working together in tightly connected networks. This indicates that HVC acts as a hub for integrating sensory and motor information, with the three types of projection neurons receiving inputs tailored to their specific role in song learning and production. Put simply, HVC-RA neurons enable the production of stable, learned songs, and HVC-X neurons are responsible for learning and modifying the song. 

The researchers also found a previously unknown connection between HVC’s presynaptic partners mMAN (medial magnocellular nucleus of the anterior nidopallium) and Av (nucleus Avalanche). This suggests that mMAN, which was previously thought to play a role in early song learning only, may also help integrate auditory feedback with motor control, allowing young birds to fine-tune their songs as they develop.

While this study provides new insights into the HVC microcircuit, which eLife’s editors say is critical for informing models of song learning and production, there are some limitations to the work. These include a potential gap in understanding the functions of developmental song learning, as the research focused on analysing the neural connections in adult birds.

“Our study provides the most detailed synaptic map to date of how different brain regions connect to HVC, a crucial centre for song learning and production,” says senior author Todd Roberts, a professor at the Department of Neuroscience, UT Southwestern Medical Center. “By revealing these wiring patterns, we’ve highlighted the synaptic networks that allow birds to structure their songs and refine their vocal skills.  The optogenetics-based mapping technique we used provides a powerful tool to explore other neural circuits, bringing us closer to understanding how songbirds achieve their remarkable vocal imitation abilities. Furthermore, because birdsong and human speech may rely on similarly organised brain circuits, this work may also pave the way to understanding more about how our brains support the learning and production of speech and language.”

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About eLife

eLife transforms research communication to create a future where a diverse, global community of scientists and researchers produces open and trusted results for the benefit of all. Independent, not-for-profit and supported by funders, we improve the way science is practised and shared. In support of our goal, we introduced the eLife Model that ends the accept–reject decision after peer review. Instead, papers invited for review are published as Reviewed Preprints that contain public peer reviews and an eLife Assessment. We also continue to publish research that was accepted after peer review as part of our traditional process. eLife is supported by the Howard Hughes Medical Institute, Knut and Alice Wallenberg Foundation, the Max Planck Society and Wellcome. Learn more at https://elifesciences.org/about.

To read the latest Neuroscience research in eLife, visit https://elifesciences.org/subjects/neuroscience.

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Journal

eLife

DOI

10.7554/eLife.104609.1 

Article Title

Synaptic Connectivity of Sensorimotor Circuits for Vocal Imitation in the Songbird

Article Publication Date

18-Mar-2025

TRANSFERANCE

A rubber hand alleviates pain

Ruhr-University Bochum

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The rubber hand is perceived as part of your own body when you can't see your own. 

 

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Credit: © Damian Gorczany

If a person hides their own hand and focuses on a rubber hand instead, they may perceive it as part of their own body under certain conditions. What sounds like a gimmick could one day be used to help patients who suffer from chronic pain: Researchers at the Clinic for Psychosomatic Medicine and Psychotherapy at the LWL University Hospital in Bochum, Germany, have shown that pain caused by heat is experienced as less severe thanks to the rubber hand illusion. They published their findings in the journal PAIN Reports from April 2025.

Heat creates illusion

The rubber hand illusion occurs when the hidden hand and the rubber hand are touched at the same time, for example with a brush. In the experiment outlined here, the illusion was not evoked through touch, but through a heat stimulus and simultaneous illumination with red light: 

In the first step, the researchers determined the individual pain threshold for heat pain in all 34 right-handed test participants. The participants then placed their left hand behind a screen so that they could no longer see it. The hand hidden by the screen was placed on a thermode head, a small plate that can be heated under controlled conditions. Instead of their left hand, a rubber hand was placed in front of the participants, which could be illuminated with red light from below. The test participants' right hand was placed on a slider which they used during the experiment to continuously rate the painfulness of the heat on their left hand. 

The researchers carried out several test runs in which they heated the thermode to several temperature levels just below the respective pain threshold, exactly at the pain threshold and just resp. significantly above it. The rubber hand was simultaneously illuminated with red light. “The heat stimulus on the left hand with simultaneous red illumination of the rubber hand evoked the illusion,” explains study supervisor Professor Martin Diers, Head of the Research Section Clinical and Experimental Behavioral Medicine. A survey of the test participants confirmed these findings after each series of experiments. In the control condition, the researchers conducted the experiment with a rubber hand rotated by 180 degrees. 

The intensity of pain decreases

“We showed that the perceived pain intensity was reduced in the rubber hand illusion condition compared to the control condition,” says Martin Diers. “We assume that the mechanism behind the rubber hand illusion is the multisensory integration of visual, tactile (here nociceptive) and proprioceptive information. The findings suggest that when people perceive the rubber hand as part of their own body, this reduces their perception of pain.” Another factor could be the phenomenon of visual analgesia, which has also been shown in other studies: A pain stimulus is perceived as less intense if the person can see the relevant part of the body while it is occurring. “However, we still don’t fully understand the neural basis for this phenomenon,” admits Diers. 

In future, the findings could possibly be used in the treatment of pain. One conceivable field of use would be the treatment of complex regional pain syndrome, for example, in which patients typically experience pain and swelling in the hand.

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Journal

PAIN Reports

DOI

10.1097/PR9.0000000000001252 

Method of Research

Experimental study

Subject of Research

People

Article Title

Time Course of the Rubber Hand Illusion Induced Analgesia

Article Publication Date

18-Mar-2025

 

Study shows rise in congenital heart defects in states with restrictive abortion laws

Researchers recommend long-term evaluation of trend and urge health systems to prepare for a larger population of CCHD patients needing complex, lifelong care

American College of Cardiology

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The incidence of babies born with serious heart defects, known as cyanotic congenital heart disease (CCHD), rose in states that enacted restrictive abortion laws following the U.S. Supreme Court’s 2022 ruling that put abortion laws in the hands of the states, according to a study being presented at the American College of Cardiology’s Annual Scientific Session (ACC.25).

The study is the first to look at rates of congenital heart defects since the Dobbs v. Jackson Women’s Health Organization ruling, also known as the Dobbs decision, which overturned the federal right to abortion and led to varying access to abortion across states. Researchers found that the incidence of CCHD held steady in states with laws protecting abortion access and rose in states with more restrictive abortion laws, exceeding model estimates of what the rates would have been without Dobbs.

“If the trend toward an increasing number of CCHD births is true, then there will be a larger population of patients with complex congenital heart disease that will need [early and lifelong] health care,” said Stephanie Tseng, MD, assistant professor and pediatric cardiologist at Nationwide Children’s Hospital in Columbus, Ohio, and the study’s lead author. “The health care system, particularly in states with restrictive policies, will need to prepare for these patients, as we know that CCHD patients have higher health care utilization needs. This includes health care costs, resources and [an increased] need for health care workers. There will be non-financial physical and emotional strains on families, as well.”

However, Tseng said that the study only shows potential associations and is not designed to identify the causes of the trends that were observed. Other factors besides abortion access could explain the differences between states, such as potential differences in prenatal care and timing of CCHD diagnosis, or differences in maternal risk factors such as diabetes that could affect the likelihood of having a baby with CCHD.

CCHD encompasses several types of heart defects that reduce the delivery of oxygen to the body. Most babies born with these conditions require intervention during the neonatal period to survive. In the current era, up to 15% to 20% of babies with CCHD die in their first year and many of those who survive require lifelong cardiology care to keep their heart working properly. This includes regular cardiology visits, testing and a potential need for additional procedures or surgeries in the future.

CCHD can typically be diagnosed on ultrasound scans performed during the second trimester of a pregnancy, although sometimes the condition is not diagnosed until after birth. The causes are usually unknown, but it is thought that genetics and environmental factors can both play a role.

For the study, researchers used birth certificate data from the U.S. Centers for Disease Control and Prevention to analyze the rates of CCHD among babies born between 2016-2024 in 20 states that enacted restrictive abortion laws and nine states with the most protective abortion policies following Dobbs.

Comparing the birth rates of babies with CCHD over time, the researchers found that rates in states with more restrictive abortion policies diverged from those in states with more protective policies in the two years following the Dobbs decision.  The median monthly overage comparing expected to observed differences was 9.6 per 100,000 births.

Another analysis quantified the degree of difference in the observed CCHD incidence over time versus the incidence that would be expected based on pre-Dobbs trends. The results showed a moderate degree of difference between observed and forecasted incidence, with most of the months post-Dobbs exceeding the average predicted incidence.

Based on the timing of when CCHD can be diagnosed prenatally and the new abortion laws, researchers said it may be plausible that the increase stems from babies being born to families who might have chosen to terminate the pregnancy if abortion were an option in their state.

“We’ve come a long way in caring for these individuals, but the mortality rate can still be high,” Tseng said. “Some of these defects can be quite severe and may not have good surgical options, and some families may consider pregnancy termination based on the outlook for the baby and the family.”

Regardless of what is driving the apparent trends, Tseng said that the study can help health care systems anticipate health care needs, as more babies being born with CCHD means that more children will require continuing care for these conditions as they grow up. Moving forward, she said it would be helpful to continue to track these trends to inform the allocation of health care resources.

Due to limitations in the data, Tseng said it is not possible to determine the specific CCHD diagnosis in each case, to know whether the condition was diagnosed before birth, or to track the exact impacts that local policies may have had. Despite these limitations, the researchers said that the findings are notable trends that warrant further long-term evaluation.

For more information on congenital heart disease, visit CardioSmart.org/congenital-heart-disease.

Tseng will present the study, “The Impact of the Dobbs Decision on Birth Rates of Infants with Cyanotic Congenital Heart Disease,” on Sunday, March 30, 2025, at 9 a.m. CT / 14:00 UTC in South Hall.

ACC.25 will take place March 29-31, 2025, in Chicago, bringing together cardiologists and cardiovascular specialists from around the world to share the newest discoveries in treatment and prevention. Follow @ACCinTouch, @ACCMediaCenter and #ACC25 for the latest news from the meeting.

The American College of Cardiology (ACC) is the global leader in transforming cardiovascular care and improving heart health for all. As the preeminent source of professional medical education for the entire cardiovascular care team since 1949, ACC credentials cardiovascular professionals in over 140 countries who meet stringent qualifications and leads in the formation of health policy, standards and guidelines. Through its world-renowned family of JACC Journals, NCDR registries, ACC Accreditation Services, global network of Member Sections, CardioSmart patient resources and more, the College is committed to ensuring a world where science, knowledge and innovation optimize patient care and outcomes. Learn more at ACC.org.

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