Microplastics Identified in Human Brain Tissue

Post by Meagan Marks

The takeaway

Microplastics and nanoplastics were found in postmortem human brain tissue at concentrations significantly higher than other organ systems analyzed, calling for further research into how these particles accumulate and affect neurological and psychiatric health.

What's the science?

Over the past half-century, the prevalence of microplastics and nanoplastics (MNPs) in our environment has risen exponentially, leading to widespread pollution and potentially harmful effects on our health. MNPs are produced when plastic products—such as clothing, food packaging, and automobile parts—break down into tiny, non-biodegradable polymers, entering ecosystems, food, water, and eventually, our bodies. 

Preclinical studies have found MNPs in the organs of animals, and have linked their presence to inflammation, toxicity, and disease. However, the implications for human health remain unclear, especially regarding the average levels of MNPs within the human body, and how they distribute across organ systems. This week in Nature Medicine, Campen and colleagues analyze postmortem human brain, liver, and kidney tissue to assess the relative concentration of MNPs in the brain and how they compare to other organ systems within the body. 

How did they do it?

To measure the concentration of MNPs in human brain, liver, and kidney tissue, the authors used pyrolysis gas chromatography-mass spectrometry, a precise technique for detecting and identifying micro and nanoparticles. They first isolated the MNPs from each sample by chemically digesting the tissue, leaving behind non-biodegradable products. The remaining solids were then compacted into a pellet and subjected to several analytical steps to determine both the quantity and identity of the MNPs present. This approach allowed the authors to compare the concentrations of various plastic types within each sample and across different subjects and organ systems. Notably, the authors included samples collected in both 2016 and 2024 to identify trends in MNP levels over the past eight years. Additionally, brain samples from patients with dementia were analyzed to assess MNP levels in neurologically diseased brains. It’s also important to note that all brain samples were taken from the frontal cortex, so more work is needed to explore MNP distributions across other brain regions. 

What did they find?

After comparing samples from the liver, kidney, and brain, the authors found that the brain contained 7-30 times as many MNPs (with a median of 3,345 micrograms per gram of sample) as compared to the liver and kidney (with median values of 433 and 404 micrograms per gram of sample, respectively). The majority of the MNPs appeared as plastic shards or flakes and were made of a specific plastic called polyethylene, a common polymer found in food packaging, bottles, and automobile parts. The brain had the highest concentration of this plastic, which made up about 75% of all MNPs. 

Interestingly, liver and brain samples from 2024 showed significantly higher concentrations of MNPs compared to the 2016 samples, with certain types of plastic—including polyethylene, polypropylene, polyvinyl chloride, and styrene butadiene rubber—specifically increasing. The total mass of these concentrations within samples had increased by 50% over the past 8 years, suggesting that environmental MNPs may be growing and leading to higher uptake by our bodies. 

Additionally, dementia patients had significantly higher MNPs than other brain samples, with a median value of over 26,000 micrograms per gram of sample. This is likely due to a more permeable blood-brain barrier and impaired clearance mechanisms, which are hallmarks of the disease. 

What's the impact?

This study found that the brain contains significantly higher levels of MNPs compared to the liver and kidney. While this discovery is important, there is still much work to be done, particularly in understanding how MNPs are taken up and dispersed throughout the brain, how they concentrate in different regions, and how they are cleared from the system. Given the rising levels of MNPs in our environment, it is crucial to investigate their potential role in neurological and psychiatric health.

Access the original scientific publication here 

How the Brain Regulates the Body’s Immune Response

Post by Meredith McCarty

The takeaway

The brain can modulate immune responses to prepare the immune system for potential threats or even induce placebo-like effects. This research reveals the functional circuitry underlying the coordination of behavioral and immunological responses in the mouse brain. 

What's the science?

The immune system is responsible for taking protective action to protect the body against perceived external threats. The insular cortex (IC) of the brain is essential for integrating sensory information with bodily states. Prior work has implicated interactions between the insular cortex and the immune system, but the underlying functional dynamics remain unknown. 

This week in Nature Neuroscience, Kayyal and colleagues use behavioral and experimental tools in mouse models to explore the role of IC in regulating immune responses.

How did they do it?

To study the interactions between the body’s immune response and sensory information, the authors utilize a conditioned immune response (CIR) task design. In this design, experimental mice are exposed to a conditioned stimulus (a specific scent) that is paired with an unconditioned stimulus that activates or inhibits the immune system. They learn the association between the scent and the unconditioned stimulus, and the researchers can study what is going on in the brain when this CIR is learned and tested. 

To study brain activity, the researchers utilize retrograde labeling techniques to identify neurons within IC that project from anterior to posterior regions (aIC-to-pIC), or posterior to anterior regions (pIC-to-aIC). They tagged these populations to quantify the degree of connectivity, and changes in connectivity across various task conditions. 

To study changes in the synaptic properties of the neurons, they conducted electrophysiological recordings from tagged neurons to quantify changes in excitability and inhibitory currents. 

To test whether aIC-to-pIC neurons are necessary and sufficient for aspects of the measured CIR, they injected modified receptors into projecting neurons to allow them to experimentally activate or inhibit specific populations of neurons and measure changes in immune and behavioral responses.    

What did they find?

When studying the immune response and behavior after CIR, they found the experimental mice had a strong aversion to the conditioned stimulus and an elevated immune response. This suggests that CIR primes the immune system for potential infection after exposure to harmful bacteria. 

When comparing the neurons that project from aIC-to-pIC and vice versa, they found an increased percentage activation of aIC-to-pIC neurons following CIR, suggesting that these insular projections play a critical role in retrieving memory associated with the conditioned scent stimulus. When quantifying the excitatory to inhibitory ratio of projection neurons, they found reduced excitability and an increased number of active aIC-to-pIC projecting neurons, highlighting a potential mechanism by which information is flexibly retrieved during the retrieval of CIR-related memories.  

Through selectively activating and inhibiting the aIC-to-pIC and pIC-to-aIC projections, they found that inhibiting the aIC-to-pIC pathway reduced learned aversive behavior. Their findings suggest that aIC regions encode taste and its conditioned response (immune system threat) and that the aIC-to-pIC pathway is necessary for the successful retrieval of the CIR. Their results highlight the importance of the aIC-to-pIC projecting neurons in modulating the body’s immune response following exposure to a conditioned aversive sensory stimulus. 

What's the impact?

This study is the first to suggest a novel role for specific regions of the insular cortex in retrieving immune-related information and flexibly tuning behavioral responses. It was previously unknown how the functional connectivity of the insular cortex relates to the body’s immune response and how the brain and body interact to promote immune function. 

Pro Soccer Players Have Unique Cognitive Abilities and Personalities

Post by Anastasia Sares

The takeaway

This study looked at professional soccer players’ cognitive abilities and personalities, finding that they differ significantly from the general population. This shows that it takes more than physical attributes to make it at the highest levels of play.

What's the science?

Professional athletes are often praised for their physical prowess, including their stamina and strength. Yet, in sports such as soccer, there are other important abilities, like keeping track of players’ positions, knowing when and where to pass, and quickly reacting to changes on the field. Not only that but becoming a competitive player involves dedication to hours of practice, as well as confidence and a healthy mentality. Previous studies have begun to quantify these traits, showing that successful soccer players perform better on some cognitive tests than the general population. Still, these studies often have small samples of professional players, or study non-professional athletes, since it’s very hard to get access to top players.

This week in the Proceedings of the National Academy of Sciences, Leonardo Bonetti and colleagues conducted one of the largest studies to date on the cognitive and personality traits of professional soccer players, showing that these traits are distinct from the general population.

How did they do it?

The authors gathered a large group of professional soccer players (over 200) and a matched comparison group from the general population. The comparison group was matched on socio-economic status and age, which are important to consider when it comes to cognitive ability. The authors administered cognitive and personality tests to the participants so that they could compare the two groups. This sample included both men and women players, as well as players from two different countries (Brazil and Sweden), so they could ensure their results were replicated across cultures.

The cognitive tests (taken from the D-KEFS and WAIS IV) were measures of what is sometimes called “fluid intelligence”—cognitive abilities that are less dependent on education. For example, digit span, a simple test of working memory, involves the participant hearing a string of numbers and then reporting back as many as they can remember. Another example is the 5-point test, which evaluates a skill called nonverbal fluency, where participants had to generate as many ways as possible to connect a set of 5 dots in a limited amount of time. A third example is the Tower of Hanoi, where participants must move a series of stacked objects to get from one configuration to another in as few moves as possible. The personality measure used in the study was the Big Five, a science-backed personality system consisting of five traits: Openness, Conscientiousness, Extraversion, Agreeableness, and Neuroticism (often known by the acronym OCEAN or CANOE).

What did they find?

The soccer players performed better than the general population on the cognitive tests: this superior performance included planning, problem-solving, and memory capacities. In the working memory test, the soccer players remembered 6 digits on average, whereas the control group could only remember just above 4 on average. The soccer players also showed higher levels of the personality traits Conscientiousness, Extraversion, and Openness to experience, along with lower levels of Neuroticism and Agreeableness.

The number of goals scored by a player was related to a high score on the 5-point test (nonverbal fluency), high Openness to experience, and low Conscientiousness. On the other hand, attempted and successful dribbles were predicted by a high digit span (working memory), a high Tower of Hanoi score (visuospatial reasoning), and high Openness to experience.

What's the impact?

This study shows that professional soccer players outperform the general population cognitively, not just physically, and that they have a specific pattern of personality traits. The authors think this could be helpful for recruiters looking for the next generation of stars. But it is unclear how these traits come about—are they the result of high-level training, or are they present before any training has begun?