In the new study, researchers combined diffusion MRI data from the Human Connectome Project with histological cross-sections of the corpus callosum, the major tract that connects the left and right sides of the brain. The Human Connectome maps the strength of all connections in the brain but does not provide the actual number of axons, while the histological cross-sections allow estimates for how many axons are packed into a given volume. Combining the connection strengths with the axon densities yielded estimates for the number of axons in the cerebral cortex.

The analysis indicated that there are almost 2.5 billion long-range axons traversing the cerebral cortex. However, despite this large number, they found that the numbers connecting different functional brain regions were quite low. For example, among the estimated 130 million axons in the arcuate fasciculus tract, only about 1 to 2 million (less than 2%) directly connected Broca’s and Wernicke’s areas, a connection which is necessary for normal language ability. The model predicts that other long connections, like those from the hippocampus to the frontal cortex that are needed for memory retrieval, are actually made in multiple steps. The findings will thus improve models of cognition, especially processes that rely on connections between distal regions of the brain.

“A major unsolved problem is how the human cortex integrates information processing by its 16 billion neurons across its surface to unify awareness,” Rosen adds. “Our finding that cortical areas are sparsely connected implies that this integration is accomplished either via linkage of the dense local connections or by rare, extraordinarily privileged long-range axons.”

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The research, published in the journal Environmental Science and Technology, suggests that wildfire emissions even 10 days old can affect the properties of aerosols — suspended liquid or particles that are key to cloud formation.

Research in aerosols and particulate matter pollution related to wildfires has most often focused on the early hours of smoke plumes, not several days later after smoke has traveled to other areas.

Enhancing modeling

This research helps fill in a knowledge gap and can inform future predictions about the climate and atmospheric effects of wildfire over the lifetime of aerosols, particularly in rural or pristine areas with relatively clean air, said Qi Zhang, an environmental toxicology professor and lead author of the study.

“These parameters are really useful for atmospheric and chemical models,” she said. “It’s a really important component to solving the effects on climate. To capture those characteristics is super critical.”

Zhang, Ph.D. student Ryan Farley and others spent time in 2019 at the Mount Bachelor Observatory atop a volcanic mountain in Oregon. That year was relatively calm in terms of wildfire, but smoke plumes and aerosols were still observed. Some were at least 10 days old and came from as close as Northern California and as far as Siberia, Russia.

The properties and chemical composition of aerosols can do a number of things: scatter or absorb solar radiation affecting temperature, seed clouds to produce rain or snow, or change the reflectivity of clouds — all of which affect climate.

Aerosol properties change with age

Scientists found that particulate matter concentrations were low, but oxidized organic aerosols from burning biomass — such as trees, grasses and shrubs — were detected throughout the samples.

The aerosols, which have a life cycle of about two weeks, were larger in aged samples compared to those found shortly after a fire starts.

“The properties of the smoke determine the effects on the climate,” Zhang said. “The really aged aerosols can behave very differently than the fresh ones. You want to capture these aerosols over the lifetime to properly account for the effects.”

Aerosols in the background

Older aerosols produced by wildfires can be present but not obvious and still affect climate.

“It’s not something you just notice but it’s in the background,” she said.

Knowing that information becomes ever more important as “biomass burning has become more and more frequent,” Zhang said.

Shan Zhou and Sonya Collier from UC Davis also participated in the research as did scientists from University of Montana and University of Washington.

The National Science Foundation, the U.S. Department of Energy’s Atmospheric System Research Program, the California Agricultural Experiment Station and UC Davis funded the research.

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“Our results underscore the need to strengthen air pollutionregulations and prevention implementation in tribal territories and areas where AI populations live,” said Maggie Li, PhD candidate in the Department of Environmental Health Sciences at Columbia Mailman School, and first author.”Until now, insight into PM_2.5 exposure burdens in AI communities has been limited, in turn contributing to the lack of air pollution epidemiological studies which include this population in the contiguous U.S.”

The researchers compared ambient PM_2.5 average concentrations and trends in AI-populated vs. non-AI-populated counties in the contiguous U.S. from 2000 to 2018. They conducted their analysis at the county level, the most relevant unit to inform regulatory action. Population data and household income were obtained from the U.S. 2010 Census.

Average concentrations were 1.46 ?g/m³ lower for modeled PM_2.5 in AI-populated counties vs. non-AI-populated counties in 2000; however, towards the end of the study period, PM_2.5 concentrations in AI-populated counties became significantly higher compared to non-AI-populated counties. By 2018, concentrations were on average 0.66µg/m³higher in AI-populated counties than non-AI-populated counties. “Although we observed that average PM_2.5 concentrations were higher in non-AI-populated counties at baseline and across most of the study period, the gap between AI- and non-AI-populated counties decreased over time; after approximately 2015, average PM_2.5 concentrations were higher in AI-populated counties,” observed Li.

Short- and long-term exposure to particulate matter ? 2.5 µm (PM_2.5) increases the risk of cardiovascular and respiratory disease, among other health outcomes. In the U.S., socioeconomically disadvantaged communities are often exposed to higher PM_2.5 exposure levels. They bear a disproportionate burden of disease, even at levels well below air quality standards set by the U.S. Environmental Protection Agency.

“Our findings build upon existing studies showing that socioeconomically disadvantaged communities experience disproportionate burdens of environmental hazards, such as ambient air pollution. Native Americans may be particularly susceptible to the adverse health effects of PM_2.5 and air pollution, but research quantifying air pollution exposures and impacts on health among this population is lacking,” said Marianthi-Anna Kioumourtzoglou, ScD, assistant professor of environmental health sciences at Columbia Mailman School, and senior author. “These communities already face a large disease burden attributable to environmental pollution due, for instance, to extensive mining and water contamination on Tribal Lands.”

Cardiovascular disease, one of the outcomes associated with exposure to PM_2.5, and the leading cause of death in AI populations, occurs at significantly higher rates than in white populations. “There is a critical need for future investigations of health impacts associated with air pollution exposure in AI populations, as well as of interventions to ensure the observed inequalities can be eliminated,” noted Ana Navas-Acien, MD, PhD, professor of environmental health sciences at Columbia Mailman School, and a senior co-author.

Co-authors are Markus Hilpert, Jenni A. Shearston, and Jeff Goldsmith, Columbia University Mailman School of Public Health; Jada Brooks, the University of North Carolina School of Nursing at Chapel Hill; Steven Chillrud, Lamont-Doherty Earth Observatory, Columbia University; Tauqeer Ali, University of Oklahoma Health Sciences Center; Jason Umans, Georgetown-Howard Universities Center for Clinical and Translational Sciences; Lyle Best and Joseph Yracheta, Missouri Breaks Industries Research, Inc.; Aaron van Donkelaar and Randall Martin, Department of Energy, Environmental & Chemical Engineering, Washington University at St. Louis.

Support for the study was provided by the National Institute of Environmental Health Sciences, grants T32 ES007322, P30 ES09089, R01 ES030616, and P42ES010349.

“Our results suggest people using statins may have a lower risk of parkinsonism and that may be partly caused by the protective effect statins may have on arteries in the brain,” said study author Shahram Oveisgharan, MD, of Rush University Medical Center in Chicago. “Our results are exciting, because movement problems in older adults that come under the umbrella of parkinsonism are common, often debilitating and generally untreatable.”

The study looked 2,841 people with an average age of 76 who did not have parkinsonism at the start of the study. Of those, 936 people, or 33%, were taking statins.

Researchers followed up with participants annually for an average of six years to check the statins they were taking and to test for signs of parkinsonism.

People were considered to have parkinsonism if they met the requirement for mild impairment for two or more of the following symptoms: tremor, stiffness, parkinsonian gait, which is marked by small shuffling steps and a general slowness of movement, and bradykinesia, a hallmark of parkinsonism which is difficulty moving the body quickly on command.

By the end of the study, 1,432 people, or 50%, developed signs of parkinsonism. Out of 936 people taking statins, 418 people, or 45%, developed parkinsonism six years later, compared to 1,014 out of 1,905 people, or 53%, of those who had not been taking statins.

After controlling for age, sex and vascular risks like smoking and diabetes that could affect risk of parkinsonism, researchers found that people who had been taking statins, on average, had 16% lower risk of developing parkinsonism six years later compared to those who had not been taking statins. About 79% of people on statin therapy were taking moderate or high intensity statins. Researchers found that people taking higher intensity statins had a 7% lower risk of developing parkinsonism compared to those on low intensity statins.

Researchers also examined the brains of 1,044 people who died during the study. They found those who had been using statins had, on average, 37% lower odds of having atherosclerosis compared to those who had not been using statins.

“More research is needed, but statins could be a therapeutic option in the future to help reduce the effects of parkinsonism in the general population of older adults, not just people with high cholesterol or who are at risk for stroke,” Oveisgharan said. “At a minimum, our study suggests brain scans or vascular testing may be beneficial for older adults who show signs of parkinsonism but don’t have classic signs of Parkinson’s disease or do not respond to Parkinson’s disease medications.”

A limitation of the study is that parkinsonism evaluations were not performed by movement disorder specialists, so cases of Parkinson’s disease may have been misclassified.

The study was supported by the National Institutes of Health.

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