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“I want children, but it’s becoming more difficult as time passes by,” a 29-year-old woman from Mexico is quoted as saying in the report. “It is impossible to buy or have affordable rent in my city. I also would not like to give birth to a child in war times and worsened planetary conditions if that means the baby would suffer because of it.”

The cerebral cortex, the outermost layer of the brain, is the central driver of various human capabilities, including decision-making, perception, language and memory. Understanding how the morphology (i.e., structure and shape) of people’s cerebral cortex is related to their mental health is a long-standing goal for many neuroscientists, as it could help to predict the risk that people will develop specific neuropsychiatric conditions while also contributing to their diagnosis and potentially informing their treatment.

Researchers at Maastricht University Medical Centre, Utrecht University and other institutes recently carried out a study aimed at unveiling causal relationships between cortical morphology and traits, including both neuropsychiatric conditions, behavioral patterns and metabolic traits. Their findings, published in Nature Mental Health, suggest that the total surface area (TSA) of the cerebral cortex and mean cortical thickness (MCT) contribute to people’s mental abilities and the development of some severe mental health disorders, respectively.

“Brain cortical morphology, indexed by its surface area and thickness, is known to be highly heritable,” wrote Bochao Danae Lin, Yunzhi Li and their colleagues in their paper. “Previous research has suggested a relationship of cortical morphology with several neuropsychiatric phenotypes. However, the multitude of potential confounders makes it difficult to establish causal relationships.”

As part of their study, the researchers analyzed a large amount of data sourced from a large genome-wide database, which was compiled as part of the Enhancing Neuro-Imaging Genetics through Meta-Analysis (ENIGMA) study. This is a brain-imaging study that collected brain imaging data, as well as psychiatric, psychological, behavioral and metabolic information from individuals living in 43 countries worldwide.

“We employ generalized summary-data-based Mendelian randomization and a series of sensitivity analyses to investigate causal links between 70 cortical morphology measures and 199 neuropsychiatric, behavioral and metabolic phenotypes,” wrote Lin, Li and their colleagues. “We show that total brain cortical surface area (TSA) has significant positive causal effects on 18 phenotypes.”

To analyze the data sourced from the ENIGMA database, Lin, Li and their colleagues employed a statistical technique called Mendelian randomization, which is useful for estimating causal relationships between traits while also controlling for potentially confounding factors. Their findings suggest that the TSA of the cerebral cortex is in fact causally related to some mental abilities, particularly their cognitive performance (i.e., how well they can memorize information, their ability to focus on specific tasks, their reasoning skills and other mental capabilities).

“The strongest effects include TSA positively influencing cognitive performance, while reverse analyses reveal small effects of cognitive performance on TSA,” wrote Lin, Li and their colleagues.

“Global mean cortical thickness (MTH) exhibits significant causal effects on five phenotypes, including schizophrenia. MTH reduces schizophrenia risk, and bidirectional causality is found between MTH and smoking initiation. Finally, in regional analyses, we detect positive influences of the transverse temporal surface area on cognitive performance and negative influences of transverse temporal thickness on schizophrenia risk.”

Overall, the results of the analyses performed by this team of researchers suggest that cortical morphology does in fact affect both people’s mental capabilities and neuropsychiatric traits. The causal relationships identified by Lin, Li and his colleagues could be explored further in future neuroscience studies, potentially helping to improve the early diagnosis and treatment of specific disorders, including schizophrenia and some cognitive deficits.

“Our results highlight bidirectional associations between TSA, MTH and neuropsychiatric traits,” wrote Lin, Li and their colleagues. “These insights offer potential avenues for intervention studies aimed at improving brain health.”

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Health Secretary Robert F. Kennedy Jr. has upended medical research and public health in the U.S. in many ways. One of the ideas that could be influencing his overhaul of federal health agencies dates back to ancient Greece.

The miasma theory is one of the first ideas that civilization hatched to try to explain why people get sick.

“It goes back to Hippocrates,” says Dr. Howard Markel, an emeritus professor of medical history from the University of Michigan, Ann Arbor. “He wrote in a book called Epidemics, that epidemics came from some type of pollution – some pollution of the atmosphere, of the air that we breathe. And hence we got terrible infectious diseases.”

This idea that, in essence, bad air caused illness was later championed by many others, including Florence Nightingale. It also led to some things that did help fight diseases, like cleaning up sewage.

But then came the germ theory — one of humanity’s big eureka moments. Scientists like Louis Pasteur and Robert Koch discovered it wasn’t some mysterious stench in the air from rotting garbage that spread diseases. Instead, it was living microscopic entities.

“They discovered what we know as germs – microbes,” says Melanie Kiechle, a historian at Virginia Tech. “Bacteria and viruses and other microscopic materials were actually what caused illness and also explained the spread of illness from one person to another. So miasma theory is debunked, essentially.”

The discovery of germs led to breakthroughs like antibiotics and vaccines.

But in a book Kennedy published about four years ago, The Real Anthony Fauci: Bill Gates, Big Pharma, and the Global War on Democracy and Public Health, the now- health secretary harkens back to the miasma theory.

“Miasma theory emphasizes preventing disease by fortifying the immune system through nutrition and reducing exposures to environmental toxins and stresses,” Kennedy writes.

But experts say one problem is how Kennedy defines miasma theory.

“I will categorically say that miasma theory, as historians of medicine and science understand it, is not what he is saying it is, period,” says Nancy Tomes, a historian of germ theory at Stony Brook University, who wrote The Gospel of Germs: Men, Women and the Microbe in American Life.

But Kennedy’s take may help explain some of his policies, especially about vaccines.

“The miasma theory is the notion that there are environmental poisons, not necessarily rotting organic matter,” says Dr. Paul Offit, a vaccine expert at the University of Pennsylvania. “For him, those environmental poisons are electromagnetic radiation, pesticides, vaccines. Vaccines are, for him, a modern-day miasma.”

And that’s dangerous, many experts say.

“Can stress, air pollution, other things, make infections worse? Yes. But the cause of infections is a microorganism,” says Dr. Tina Tan, who heads the Infectious Disease Society of America. “It’s the microorganisms that are making people sick.”

And vaccines have clearly been shown to safely and effectively protect people against dangerous microorganisms, Tan and others say.

“He’s trying to give this false veneer of intellectualism by saying, ‘Oh, the miasma theory,’” says Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Bloomberg School of Public Health Center for Health Security. “This all just obfuscation to support his idea that vaccines are not valuable.”

But some other observers argue that Kennedy’s ideas about the miasma and germ theories aren’t necessarily mutually exclusive.

“The real debate here is whether we can solve public health problems by developing treatments like vaccines, antibiotics, or other drugs? Or whether we will solve these problems by strengthening people’s immune systems through healthier habits?” says Gregg Girvan, a resident fellow at the Foundation for Research on Equal Opportunity, a Washington think tank. “And my response is, ‘Why can we not acknowledge that there is truth in both positions?’”

Kennedy’s office did not respond to NPR’s request for more information about his views about the miasma and germ theories.