The contrast is striking because cortical thinning is generally associated with normal aging and, when accelerated in specific areas, with neurodegenerative disease. The cerebral cortex is the brain’s folded outer layer, containing networks involved in memory, language, attention, decision-making and sensory processing. In Alzheimer’s disease, damage often emerges in a characteristic sequence that includes the entorhinal cortex, which serves as an important gateway for memory networks, followed by temporal and other cortical regions. In the new study, researchers focused on a composite measure encompassing the entorhinal, fusiform, inferior temporal and middle temporal cortices—areas known to be especially susceptible to Alzheimer’s-related changes.

The study combined data from two independent research groups that differed substantially in both age and sex. One group included 387 men from the Vietnam Era Twin Study of Aging, with an average age of about 62 years. The other consisted of 1,097 women participating in the Women’s Health Initiative Memory Study, whose average age was approximately 78. Using participants’ residential histories, the researchers estimated exposure to outdoor PM2.5 and NO2 during the three years preceding each person’s MRI scan. PM2.5 refers to airborne particles no larger than 2.5 micrometers in diameter—roughly one-thirtieth the width of a human hair. Because of their small size, these particles can penetrate deep into the lungs and may trigger systemic biological effects. Nitrogen dioxide is a reactive gas produced largely by fuel combustion, particularly from traffic and other urban sources.

Among the older women, higher exposure to both pollutants was associated with a thinner cortex across the Alzheimer’s-vulnerable regions. The researchers calculated that each additional microgram per cubic meter of PM2.5 exposure corresponded to an estimated cortical-thickness difference comparable to approximately 13 months of aging. For NO2, each additional part per billion was associated with a difference comparable to roughly three months of aging. These comparisons do not mean that pollution literally adds a fixed number of months to a person’s biological age, nor do they establish that exposure caused the tissue changes. Instead, they provide a way to express the size of the statistical association relative to typical age-related differences in cortical thickness.

The pollution signal was not limited to the four Alzheimer’s-related regions. In the older women, higher PM2.5 exposure was associated with a thinner cortex in 23 of the 34 brain regions examined, spanning the frontal, parietal, temporal and occipital lobes. Such a widespread pattern suggests that the effects of air pollution, if confirmed, may involve broad brain systems rather than a single memory circuit. Potential pathways include inflammation, oxidative stress, impaired blood-vessel function and disruption of the blood-brain barrier, a selective cellular interface that helps regulate which substances enter nervous tissue. Fine particles may also influence the brain indirectly through the lungs and bloodstream, although the present study did not measure the biological mechanisms responsible for the observed associations.

The younger men displayed a very different pattern. In this group, greater exposure to PM2.5 and NO2 was associated with a thicker cortex in the Alzheimer’s-vulnerable regions. While a thicker cortex is often interpreted as a sign of healthier brain tissue, that assumption is not always reliable. Some research suggests that cortical thickening can occur during early phases of certain disease processes, potentially reflecting inflammation, fluid-related swelling, enlargement of glial or neural cells, or other compensatory responses. Early pathological changes related to amyloid accumulation may also alter brain structure before later neurodegeneration produces measurable thinning. However, the study did not measure amyloid, tau, inflammation or other biomarkers, so none of these explanations can be confirmed.

An age-related analysis offered a possible clue to the divergent findings. Among the men, the positive association between PM2.5 exposure and cortical thickness gradually weakened between approximately ages 55 and 64 and became negative after around age 65. The later negative association was not statistically significant, meaning the evidence was insufficient to rule out the possibility that it resulted from chance. Even so, the trajectory raises the possibility that the brain’s structural response to pollution may change over the course of aging. A temporary thickening phase could represent an early biological reaction, followed by thinning as damage accumulates. This interpretation remains a hypothesis rather than a demonstrated sequence, because the participants were assessed at a single point in time rather than repeatedly over many years.

The researchers emphasize that the study cannot determine whether age, sex or other differences between the two groups explain the contrasting results. The participants came from separate cohorts with different demographic, health and life-history characteristics, and the analysis was observational. Residential pollution estimates also represent modeled exposure rather than direct personal measurements and may not capture time spent indoors, occupational exposure, indoor pollution, individual activity patterns or differences in pollutant composition. In addition, brain structure can be influenced by education, cardiovascular health, genetics, socioeconomic conditions, smoking, physical activity and many other factors. Statistical associations in MRI data therefore cannot be interpreted as proof that air pollution directly caused cortical injury or that the participants will develop Alzheimer’s disease.

Even with these limitations, the findings add to a growing body of research linking environmental exposures with brain aging and dementia-related biology. Air pollution is widespread, persistent and potentially modifiable through changes in transportation, energy production, urban planning and public-health policy. The study’s senior investigators argue that advanced neuroimaging can help identify possible effects of pollution years before dementia symptoms become visible. The next stage of research will require longitudinal studies that follow men and women from the same cohorts over time, repeatedly measure pollution exposure and brain structure, and include biomarkers for amyloid, tau, inflammation and vascular injury. Researchers will also need to track cognitive performance to determine whether pollution-related cortical changes predict memory decline or elevated Alzheimer’s risk. Until those studies are completed, the central message is one of caution: air pollution may leave a measurable imprint on the aging brain, but that imprint may not be uniform—and a thicker cortex at one stage of life may not necessarily signal better brain health.

Subject of Research: People

News Publication Date: 14-Jul-2026

Web References: https://ini.usc.edu/ ; https://keck.usc.edu/faculty-search/lauren-salminen/ ; https://doi.org/10.1016/j.neuro.2026.103495

References: NeuroToxicology, DOI: 10.1016/j.neuro.2026.103495

Image Credits: Stevens INI

Keywords: Air pollution, PM2.5, nitrogen dioxide, NO2, Alzheimer’s disease, cortical thickness, brain aging, neuroscience, environmental health, neurodegeneration

Published recently in the prestigious journal Nature Cardiovascular Research, this study introduces a groundbreaking MRI technique that harnesses ultra-high field 7 Tesla (7T) magnetic resonance imaging to quantify cerebral microvascular volumetric pulsatility in unprecedented detail. By capturing dynamic changes occurring over the cardiac cycle, this approach is the first of its kind to measure microvascular pulsations in living humans safely and noninvasively, bombarding conventional limitations that confined prior investigations primarily to animal models.

At the core of this innovation lies the integration of two advanced MRI techniques: vascular space occupancy (VASO) imaging and arterial spin labeling (ASL). VASO sensitively captures blood volume changes by exploiting differences in blood and tissue magnetization, while ASL noninvasively labels arterial blood water molecules as endogenous tracers, enabling precise tracking of cerebral blood flow. The marriage of these modalities allows detection and high-resolution mapping of volumetric changes in the brain’s microvessels across different cortical layers and white matter regions over time.

This technique has revealed compelling evidence that microvessel pulsatility increases with age, particularly in the brain’s deep white matter—an area critical for the communication of neural signals between brain networks. Deep white matter has long been known to be vulnerable to reduced blood supply from distal arteries as people age. These arteries channel oxygenated blood into the farthest reaches of the brain, and their diminishing function is associated with cognitive decline and neurodegeneration. Enhanced pulsatility in these microvessels might contribute to this pathological process by disrupting the delicate vascular environment and affecting brain homeostasis.

Dr. Danny JJ Wang, professor of neurology and radiology and lead senior author of the study, explains that arterial pulsation serves as the brain’s natural pump, facilitating fluid movement and waste clearance essential to brain health. The novel imaging method provides detailed volumetric data for these microscopic vessels, marking a monumental step forward in evaluating how vascular factors influence brain function throughout aging. This advancement is crucial for elucidating the relationships between vascular health and neurodegenerative diseases, such as Alzheimer’s, where compromised microcirculation plays a significant role.

For decades, researchers have understood that increasing stiffness and pulsatility in large arteries are linked to cerebrovascular disease, stroke, and dementia. However, until now, translating these observations to the scale of the brain’s microvessels has remained unattainable due to methodological constraints. The USC team’s breakthrough pushes the frontier by elucidating how microvascular dynamics change in vivo in humans and how these alterations correlate with aging and vascular risk factors such as hypertension.

The research led by postdoctoral researcher Fanhua Guo identifies that older adults exhibit significantly heightened microvascular volumetric pulsations, especially when combined with hypertension. This finding is essential because it bridges the explanatory gap between observable large vessel impairments and the microvascular damage often implicated in aging-related cognitive decline and Alzheimer’s disease. By quantifying these subtle vascular volume changes over the cardiac cycle, the study uncovers new biomarkers that could predict disease progression and target interventions effectively.

Beyond vascular mechanics, excessive microvascular pulsatility may disrupt the function of the brain’s glymphatic system—a recently characterized network responsible for clearing metabolic waste including beta-amyloid proteins that accumulate in Alzheimer’s disease. Dysregulated vascular pulsations could impair glymphatic clearance mechanisms, leading to the accumulation of neurotoxic waste and accelerating the progression of cognitive decline. This link offers profound insights into how vascular health directly influences neurodegenerative pathology.

Arthur W. Toga, director of the Stevens INI, emphasizes the significance of this ability to quantify microvascular pulses in living humans as an enormous leap forward. This novel technology not only enriches our understanding of the aging brain but also holds immense promise for early diagnosis, personalized monitoring, and therapeutic interventions for neurodegenerative diseases, thus potentially transforming clinical neurology and preventive medicine.

Currently, the USC research team is exploring the applicability of this MRI technique in more widely available 3 Tesla MRI systems, which have a broader presence in clinical settings globally. If successfully adapted, this would allow the method to be deployed for routine screening and monitoring of at-risk populations, thus accelerating translational impact from the laboratory to bedside clinical practice.

Future investigations aim to refine the measurement of microvascular pulsatility as a predictive biomarker for cognitive decline and Alzheimer’s disease. This could revolutionize early intervention strategies, enabling clinicians to identify vascular dysfunction before irreversible neurodegenerative damage occurs. Such predictive capability would facilitate timely therapeutic interventions, improving outcomes and quality of life for millions of individuals worldwide.

In conclusion, this advancement marks the dawn of a new era in cerebral microvascular imaging—a transformative tool with the potential to illuminate unseen aspects of brain health and disease. Dr. Wang remarks that their ultimate goal is to integrate this technology into everyday clinical practice, offering new hope for diagnosis, prevention, and treatment strategies in the fight against dementia and related neurological disorders.

Subject of Research: Cerebral microvascular volumetric pulsatility and its implications for brain aging and neurodegenerative diseases

Article Title: Assessing cerebral microvascular volumetric with high-resolution 4D cerebral blood volume MRI at 7 T

News Publication Date: 25-Sep-2025

Web References:
https://www.nature.com/articles/s44161-025-00722-1
http://dx.doi.org/10.1038/s44161-025-00722-1

References:
Guo, F., Zhao, C., Shou, Q., Jann, K., Shao, X., Jin, N., & Wang, D. J. J. (2025). Assessing cerebral microvascular volumetric with high-resolution 4D cerebral blood volume MRI at 7 T. Nature Cardiovascular Research. https://doi.org/10.1038/s44161-025-00722-1

Image Credits: Stevens INI

Keywords: Brain, Microvessels, Alzheimer disease, Dementia, Cognitive disorders, Magnetic resonance imaging, Blood vessels