Yanwen’s blog

8/4/2026

Yesterday I wrote that the prefrontal cortex is one of the last major brain regions to mature, with its structural and functional development continuing through adolescence and into the third decade of life.

But development doesn't stop there. The brain remains plastic throughout life. Learning, experience, and our environment can continue to reshape neural connections and brain function.

That means how we live matters.

Healthy habits such as adequate sleep, regular aerobic exercise, mindfulness, and sustained mental engagement can support cognitive and prefrontal function. 

Chronic stress, sleep deprivation, and prolonged social isolation, on the other hand, are associated with changes in brain structure and function, including in regions involved in decision-making, social cognition, and emotional regulation.

Studies indicate prolonged social isolation reduces grey matter density within the prefrontal cortex. Loneliness may feel like an emotion, but research suggests that chronic loneliness is associated with measurable changes in the brain, including areas involved in decision-making, social cognition, and emotional regulation. 

Another factor deserves special attention: our information diet.

Informational junk food: Short-form videos, constant notifications, and algorithmically curated feeds are designed to capture attention and encourage rapid, repeated engagement. They require little sustained concentration and can train us toward constant stimulation and instant gratification.

Just as our physical bodies are shaped by what we repeatedly consume, our minds are shaped by what we repeatedly pay attention to. If we spend hours jumping from one short video to another, our ability to sit quietly with a book, think through a difficult problem, or sustain a conversation may suffer.

That doesn't mean dopamine “pleasure chemical” simply “overpower” our PFC.

Dopamine plays an important role in motivation, learning, and reward prediction. It can increase the anticipation and pursuit of a rewarding experience. That's one reason an endless stream of potentially interesting videos can keep us scrolling: believing the next one might be better.

Over time, repeated behaviors can also become habits. Brain circuits involving the striatum and other regions help automate familiar behaviors, reducing the need for conscious deliberation each time we perform them.

That's why mindlessly opening a short-video app can feel almost automatic. We don't necessarily make a fresh decision every time. The habit has made the decision easier.

So perhaps the answer is to design our environment and habits so that our better judgment gets a chance to operate.

Get enough sleep. 

Exercise regularly. 

Spend time with real people. 

Read something longer than a few minutes.

Work on one thing without constantly switching. 

And protect some part of each day from algorithmic feeds and notifications.

Even thirty minutes of uninterrupted reading, writing, thinking, or face-to-face conversation can be a small act of resistance against constant stimulation.

We spend a great deal of effort taking care of our bodies. We should be equally taking care of the part of our brain that helps us pause, think, choose, and decide what kind of person we want to become.

8/3/2026

Recently I came across a buzzphrase on the Chinese internet:

“与前额叶健康的人做朋友”
Yǔ qián é yè jiànkāng de rén zuò péngyou
— “Make friends with people who have healthy prefrontal cortices.”

The phrase has spawned all kinds of humorous variations, such as “stay away from people with underdeveloped prefrontal cortices” and “check someone's prefrontal cortex before starting a relationship.”

Behind the joke is a fascinating piece of neuroscience.

The prefrontal cortex (PFC) is one of the most advanced regions of the human brain and one of the last to mature. It is heavily involved in what neuroscientists call executive functions: planning, decision-making, working toward long-term goals, inhibiting inappropriate impulses, and regulating behavior.

The PFC is also unusually large in humans. Depending on how it is defined, it has been estimated to account for up to about 29% of the human cerebral cortex, compared with about 17% in chimpanzees. The exact numbers vary according to the anatomical definition being used, but the broader point is clear: the human PFC is exceptionally expanded relative to that of other primates.

In everyday life, we might think of the PFC as the brain's management center.

It helps us pause before reacting in anger.

It helps us weigh costs and benefits before making a decision.

It helps us work backward from a goal and formulate a plan.

It helps us consider another person's perspective rather than seeing everything only from our own point of view.

It also helps us regulate our emotional responses.

This is where the PFC's relationship with the amygdala becomes interesting. The amygdala is involved in detecting emotionally significant or threatening stimuli and can contribute to rapid emotional responses such as fear. The PFC and other brain regions interact with the amygdala in regulating these responses.

In simple terms, however, the metaphor of the brake is useful. 

When someone insults us, our first impulse may be to strike back.

When we are angry, we may want to say something hurtful immediately.

When we see something we want, we may want it that moment.

A well-functioning regulatory system gives us the ability to pause, think of consequences and ask: “What happens if I act on this impulse?”

That may be what the Chinese internet saying is really getting at when it says, “Make friends with people who have healthy prefrontal cortices.”

It means we might want to spend time with people who can remain calm when emotions run high, think before they speak, consider consequences, listen to other perspectives, and resist every passing impulse.

We should choose friends not only for how much fun we have with them, but also for how they influence the way we think and behave.

And if the PFC is so important, an interesting question naturally follows:

What can we do to keep our own prefrontal cortex healthy and strengthen our ability to think before we act?

That's what I'll explore tomorrow.

8/2/2026

Yesterday I read several articles about friendship, and they made me think about an interesting irony of getting older.

Here are some of them: "Bumble - Bumble For Friends Data Shows Importance of New Friendships, Including Those Made Online, to Combat Loneliness", AARP article "Friendships Are Still Important Regardless of How People Connect", from American Survey Center "Disconnected: The Growing Class Divide in American Civic Life - The Survey Center on American Life", "The State of American Friendship: Change, Challenges, and Loss - The Survey Center on American Life," and "American Men Suffer a Friendship Recession."

The key idea is: the older we become, the more difficult it can be to make new friends—yet friendship remains just as important, if not more important, to our well-being.

AARP's 2026 Friendship Study paints an interesting picture of the importance of friendship in American life. It found that 95% of U.S. adults say friends are essential to a happy and healthy life, up from 90% in 2019—a five-percentage-point increase. The study was based on a nationally representative survey of 1,488 U.S. adults age 18 and older.

Another interesting finding is that 54% of adults reported having friends from another generation—at least 15 years older or younger. This suggests that friendship doesn't necessarily have to be confined to people our own age. Intergenerational friendships can broaden our perspectives and strengthen our emotional support networks.

This connects surprisingly well with the idea behind SHARE Kanazawa that I wrote about yesterday: perhaps we should create more opportunities for people of different generations to live, work, and interact together.

But while people continue to value friendship, making new friends seems to be getting harder.

Bumble conducted a survey of more than 1,000 U.S. adults who had attended or were attending college. Fifty-two percent said they had not made a single new friend during the previous year. At the same time, 60% said they wanted to make new friends.

That contrast is striking: many people want new friendships, but more than half hadn't made even one new friend in the preceding year.

The long-term trend is even more disturbing.

The Survey Center on American Life compared its 2021 American Perspectives Survey with a national survey conducted in 1990. It found that the share of Americans reporting that they had no close friends had quadrupled—from just 3% in 1990 to 12% in 2021.

More recent research from the same organization found that the figure had risen further to 17% in 2024, up from 12% in 2021.

The numbers tell a striking story:

3% (1990) → 12% (2021) → 17% (2024)

The Survey Center on American Life has described this broader trend as a "friendship recession." Daniel A. Cox used the term to describe the decline in Americans' friendship networks over recent decades.

There is a revealing fact of life here.

As people get older, their social networks tend to shrink. At the same time, they continue to place enormous value on friendship. AARP's finding that 95% of adults consider friends essential to a happy and healthy life makes this contrast especially striking.

Why does making new friends become harder?

There are certainly many possible explanations. But one obvious factor is time.

Friendship takes time. We need repeated encounters, conversations, shared experiences, time spent together, and gradually developing trust before an acquaintance becomes a real friend.

When we are young, friendship often happens almost automatically. School, college, dormitories, sports teams, clubs, and other activities put us in the same places with the same people again and again. We don't necessarily have to make a conscious effort to "find friends." Friendship grows out of proximity and shared experiences.

As we get older, that machinery of friendship begins to disappear.

We graduate from school. We build careers, get married, raise children, move to different cities. Our daily lives become increasingly organized around work and family.

We may have less time, fewer opportunities, and fewer natural settings in which to meet new people repeatedly.

Friendship, like almost everything else that matters, doesn't happen without time.

As we grow older, perhaps one of the best things we can do for ourselves is not only to keep our old friends, but to keep making room for new ones.

8/1/2026

I recently read parts of Lonely Society (The Upcoming Fifth Consumer Era) by Atsushi Miura. One part in the book particularly made me think.

Japanese society faces a difficult problem: a huge number of young people have to provide care for family members. This can place a heavy burden on children and young adults, especially in a society facing both an aging population and growing loneliness.

Sociologist Atsushi Miura proposed turning the conventional one-way model of caregiving upside down. He calls it shared caregiving.

Instead of one young person struggling to support several elderly people, why not have several older people collectively support one young person?

Older residents might provide affordable housing, home-cooked meals, life experience, professional connections, and companionship.

Young residents, in return, might help older people with grocery shopping, household chores, transportation, and other physically demanding tasks.

The key is that both generations give and receive.

One example is SHARE Kanazawa, a community in Kanazawa that brings together elderly residents, people with disabilities, university students, and others. Students receive below-market housing in exchange for contributing time to the community and helping elderly residents.

One anecdote from SHARE Kanazawa is particularly unforgettable to me.

An art university student moved into the community determined to do everything she could to help the elderly residents. But soon, something else happened. The elderly women began bringing her homemade pickles, freshly baked pastries, vegetables from their gardens, and other treats.

Eventually, she realized that she wasn't simply there to help them. They were also taking care of her. She said it was the first time she had truly felt that someone cared about her well-being in the big lonely city.

This story impressed me for two reasons.

First, care can be mutual.

We often think of intergenerational care as a one-way relationship: the young take care of the old.

But the anecdote shows a different story. The young can provide the physical help that older people need, while older people can provide something the young may desperately need as well: warmth, attention, companionship, food, encouragement, and the feeling of being cared about.

Second, older people need more than care. They need a sense of dignity and usefulness.

The elderly residents are not simply useless people waiting to be cared for. They still have skills, experience, generosity, and love to offer.

They demonstrate that: They still have something to give and can still make someone happy.

Perhaps this is something we sometimes overlook when we talk about aging. We focus so much on what older people need from society that we forget to ask what they can still give to society.

Ultimately, people don't only need to be cared for. They also need someone to care for. They need to feel useful, needed, and valued in society.

A healthy community may be one in which people of different ages and abilities have reasons to depend on one another.

The young may need the strength and energy of youth. The old may offer wisdom, experience, generosity, and warmth.

The real answer to loneliness may not be simply to provide more services, but to create more opportunities for people to care for one another.

After all, sometimes the person we think we are helping may be helping us just as much.

一读者问：“ 对爷奶替背书包上学的一代来说，能指望他们的多少给与呢？” 好问题！爷奶替背书包的现象，大概只有中国有

7/31/2026

Yesterday I was rather disturbed when I read some new medical research about biological aging and early-onset cancer. I especially wanted to share the findings with the younger generation.

A study published last month in Nature Medicine, titled "Biological aging and generational shifts in early-onset cancer risk," analyzed 154,169 participants from the UK Biobank, with partial validation in more than 10,000 participants in the U.S.

The researchers compared people from different birth cohorts using several measures of biological aging, including PhenoAge, the Klemera-Doubal method, and metabolomic measures.

The results:

In the UK data, people born between 1965 and 1974 had a 23% higher standardized PhenoAge age gap than those born between 1950 and 1954. In other words, at the same chronological age, people in the more recent birth cohorts appeared to have more advanced biological aging. The pattern was also seen in the U.S. data: people born between 1990 and 1999 had a substantially higher PhenoAge age gap than those born between 1965 and 1969.

More importantly, greater biological aging was associated with a higher risk of early-onset solid cancers. Each standard-deviation increase in the PhenoAge age gap was associated with an 8% higher risk of early-onset solid cancer in the UK cohort. The researchers also found associations between immune-tissue aging and early-onset lung cancer, and between adipose-tissue aging and early-onset colorectal cancer.

Another recent review, "Early-onset colorectal cancer as an emerging disease of metabolic dysregulation," points to a related concern: early-onset colorectal cancer has been increasing, particularly in high-income countries, at the same time that obesity and metabolic disorders have become more common among younger people.

Researchers are investigating whether obesity, insulin resistance, chronic inflammation, altered gut microbiota, sedentary lifestyles and poor diet may contribute to an environment that makes colorectal cancer more likely.

We should be careful, however. These studies do not prove that overeating or obesity directly causes the generational increase in biological aging or early-onset cancer. Cancer has many causes, and the researchers emphasize that the full explanation remains unknown. Other possible contributors include alcohol, sleep disruption, environmental exposures, socioeconomic conditions and factors that scientists have not yet identified.

Still, there is an important lesson here.

I think about what my 95-year-old mother has told me about her childhood, youth and most of her adult years. Her generation experienced famine and malnutrition. Today's younger generation lives in almost the opposite environment: food is abundant, inexpensive and available all the time. Nutrition is way too much.

That transformation is one of humanity's great achievements. But abundance brings its own challenge. Together with it is new food processing technologies making it harder to resist over eating.

For greater part of human history, the problem was food shortages. Today, we live in an age of abundant food, but our bodies have not evolved quickly enough to adapt to this abundance.

Perhaps we need to learn a new kind of discipline: just because we have more does not mean we should eat more.

We cannot control every environmental factor that may influence biological aging or cancer. But we can control some of the basics: how much we eat, what we eat, how active we are, how much we sleep, and whether we allow excess weight and metabolic problems to develop.

My hope is that the younger generation can enjoy the abundance without becoming victims of that abundance.