The (Micro)Plastic Brain

The Plasticene - in living wire - plastic mushrooms

Photo by Maxim Berg on Unsplash

The Plasticene

Humanity has left its mark on planet Earth.

So much so that ‘Anthropocene’ has become a popular way to refer to the current geological period — the age indelibly stamped by humans. In 2024, the name was formally rejected as a geological stage, but it remains a popular shorthand for our pervasive effect on the planet. One reason the International Commission on Stratigraphy rejected the Anthropocene is that it’s not clear what we would use as a starting point. The first atomic bomb? The Industrial Revolution? Human-driven mass extinctions? Large-scale agriculture?

What about plastics?

Starting with the first fully synthetic plastic Bakelite in 1907, plastics have taken over the world. Some researchers even propose to call our age the Plasticene. Plastics are resilient and, like sand during a day at the beach, they get everywhere.

Water and sediment samples taken during 2016 and 2017 expeditions to the Mariana Trench (down to 10,908m) revealed 200 to 2,200(!) pieces of plastic per liter of water/sediment, even in the deepest samples. In 2022, an average of almost 30 pieces of airborne microplastics were found per liter of fresh Antarctic snow. A recent preprint of 51 post-mortem human brain samples found microplastics¹ in all of them. The 2024 samples were up to 0.5% plastic by weight. Mariana Trench, Antarctic snow, human brains (and testicles)...

That can’t be good.

Yet, the harms of microplastics to human health are still a question mark. In lab mice, we know that microplastics are neurotoxic, affecting learning, memory, and social behavior. In brain organoids derived from human stem cells, we can observe the detrimental effects of microplastics too. Direct causal evidence in living, breathing humans is harder to come by. Still, microplastics increase the risk of cardiovascular problems in people who already have carotid plaques and people with inflammatory bowel disease have a higher concentration of microplastics in their feces than people without the condition.

Correlation is not causation and lab animals or organoids are not humans, but the circumstantial evidence for detrimental effects of microplastics on human health is piling up rapidly. As is the plastic.

And that might be a problem for one of our brain’s most amazing abilities: plasticity.

In living wire

Our brains are remarkable. Billions of neurons make trillions of connections through synapses. Squirming, living, learning, our brains incessantly reshape themselves in response to combinations of incoming stimuli — an ability called neuroplasticity². Our skull blobs are one of our greatest assets³.

Culture, social environment, physical activity, dance, meditation… I could write another few thousand words to list all the stimuli and behaviors that help (or disrupt) our brains in reshaping themselves and still only scratch the wrinkly surface.

What about microplastics?

Again, in humans, we don’t know. In mice, however, microplastics negatively affect synaptic pruning (removing unnecessary connections) in early development. Even more, maternal exposure to microplastics screws up synaptic plasticity in the baby mice.

Still, we don’t know for certain if microplastics affect neuroplasticity in human brains, but we do know that chronic psychological stress does. Depressed brains also show a decrease in neuroplasticity. One of the things that happen in a depressed brain is that it becomes more modular — it almost literally gets stuck in a negative loop. Pessimistic thought patterns, negative fixations, and so on are less attenuated by input from other brain networks. This has prompted some researchers to consider adult neuroplasticity as a ‘cure’⁴ for major depression.

How do we ensure that our brains are the good kind of plastic?

It’s not a big secret. A glance at the science suggests cognitive training, physical activity, and pharmaceutical interventions. Also, sleep. Move your body⁵ and use your brain and then give them both time to rest and recover.

A more experimental approach I can’t resist mentioning because it sounds cool is neural sculpting, which is based on biofeedback. In broad strokes, by showing people their own brain activity (via fMRI), they can use,

… neurofeedback for the more radical goal of sculpting categories that did not previously exist in the brain.

… including the distant possibility of sculpting more extensive knowledge and/or complex categories or concepts in the human brain, bypassing experience and instruction.

Very speculative, but also very intriguing.

Time for mushrooms.

Plastic mushrooms

What could also induce neuroplasticity are psychedelics. LSD, psilocybin, and ayahuasca are all enjoying a resurgence in popularity at the moment for their potential as (partial) treatments for a variety of psychological conditions, like depression, anxiety, and so on. Keyword: potential. The research on psychedelics for treating mood disorders is relatively sparse and often marked by small sample sizes, short durations, or methodological issues.

Neuroplasticity is a possible mechanism for this (suggested) beneficial effect of psychedelics and a 2023 study gives us a glimpse at the magic in magic mushrooms. In cell cultures, both psilocybin and DMT bind to intracellular serotonin receptors (5-HT2AR), which can induce neuroplasticity. Translation: like special keys, psychedelics bind to specific locks on brain cells, which allows these cells to make new connections.

By breaking down brain barriers, some psychedelic compounds might reintegrate a depressed mind. This induced neuroplasticity could also be why many people report their selves dissolving when on a trip.

Might, possibly, some… I’m not only using those qualifiers because there are only a handful of things in life I’m certain of, but also because the science of psychedelics is very much in its early stages. We need a lot more high-quality, double-blind trials before we can say anything about doses, administration schedules, adverse effects, comparisons to other treatment methods, and so on.

Yet, mushrooms might not only help us with neuroplasticity. They can help us with microplastics too.

Many methods of slurping up microplastics are under investigation, including several based on biomaterials. Sounds like a job for fungi⁶. For example, pellets of the common fungus Aspergillus niger can remove a range of microplastics from water, with the researchers going as far as claiming that including those fungal pellets in wastewater treatment “can reduce 90 % of global aquatic microplastic.“

There is a but.

Fungi that like microplastics as artificial habitat (aka ‘plastiphilic’ fungi) are more likely to be human pathogens. Could the fight against plastics also become the battle of the fungi? Or is my brain running away with me again?

Maybe my brain is simply being plastic.

Do you know what’s good for neuroplasticity too? Reading Subtle Sparks. Do you know what’s even better? Clicking buttons. (Disclaimer: claims are hypothetical.)

1. Officially, microplastics are smaller than 5mm, nanoplastics are smaller than 1μm.

2. There are two main types of neuroplasticity: structural (‘shape’) and functional (‘connections’).

3. And, for some of us, our greatest enemies. Or best enemies, maybe. Song alert: Ma Meilleure Enemie by Stromae (Belgium represent!) and Pomme.

4. Not a fan of ‘cure’ in this context. Like unhappy families, each depression is a unique constellation of symptoms. Different people with depression respond differently to different treatment options.

5. Dancing seems to be an excellent option, with positive functional and structural effects on the brain. Makes sense; dancing involves strength, endurance, and proprioception.

6. Mushrooms are the fruiting bodies of fungi. Champignons for dinner? Ooh la la (read in a French accent). You’re chomping down on fungus fruits.