Every City Has a Nervous System

The first thing New York took from me on my last visit was my MetroCard.

I had kept an old one and brought it with me, although I had no idea whether there was any money left on it. At the turnstile after the AirTrain, I fed it into the machine to find out.

The machine kept it.

There was no error message that I remember, and no opportunity to retrieve it. The card went in and simply did not come back.

The MTA had been rolling out OMNY, its tap-to-pay fare system, for years. MetroCard sales had ended at the end of last year, although existing cards were still being accepted while the system completed the transition. Mine may simply have expired. Either way, I did not even get to keep it as a souvenir.

The interface I remembered no longer worked, but the strange thing was how much of everything behind the interface still did.

Once I was on the subway, the old logic returned almost without asking: how to read the platform, which car to board for optimal transfer, where to stand to be in front of the doors when the train arrives, and when someone ahead of me was walking slowly enough to go around without hitting them with my carry-on.

I had lived in New York for many years, and those movements did not feel like decisions when I lived there. They barely felt like decisions when I returned.

The card was obsolete.

The operating instructions were still somewhere in my body.

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The city I remember is not the city I meet

I arrived in New York as a young adult, and the intensity was part of the attraction.

Noise was not only noise. It was evidence that something was happening.

Density meant people, possibility, work, music, restaurants, ideas, arguments, neighborhoods, industries, cultures, and the feeling that almost anything could be found somewhere if you knew how to move through the city.

Speed had utility. You learned to navigate complexity because complexity was everywhere.

The city asked for a lot, but many of those demands developed capacities I was there to develop: moving quickly, processing information, reading people, switching contexts, finding opportunity, and tolerating friction. What might have looked exhausting from the outside felt like expansion from the inside.

I would be suspicious of any retrospective story in which all of that was secretly bad for me and I was simply too young to notice. It was not.

New York gave me an enormous amount. But the New York I experienced during the pandemic felt different again because the conditions had changed, and so had the meaning of density, proximity and movement. Many of my friends left. Many remain.

Now, when I return, I sometimes find myself wondering how I was able to live there for so long. I notice the noise almost immediately, not to mention the ripe smell of summer garbage in Koreatown.

These are not signs of New York becoming worse. The more uncomfortable possibility is that the city and I no longer meet each other in the same way.

A place can be coherent with one stage of life and increasingly expensive in another, without deteriorating at all.

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A city begins before choice

We tend to think of cities as containers for life: we choose where to live, then live our lives there.

But much of a city reaches us before anything resembling a deliberate choice occurs. Morning light reaches the bedroom, traffic reaches the window, and the distance to the grocery store determines whether an errand includes twenty minutes of walking or forty minutes in a car.

A public transportation system changes how far away another person feels. Opening hours influence when streets become active. Weather changes where people gather. Public spaces affect whether social contact happens incidentally or has to be scheduled. Food infrastructure influences what counts as an easy meal, while noise changes what the body has to ignore.

None of these things determines what a person will do, but together they change the cost of doing it.

Research across fourteen cities has found measurable relationships between features such as residential density, street connectivity, public transport and access to parks, and how much people actually move. The World Health Organization treats transport, noise, air pollution, green space and opportunities for walking and cycling as health conditions, not merely urban amenities.

This should not be surprising.

If one environment includes movement inside the ordinary business of living while another requires a separate decision to exercise, the two environments are asking different things of the individual. One requires movement; the other requires motivation.

Over enough years, that difference compounds.

I had already been noticing this through food. In “In Lima, Convenience Still Looks Like Food”, I wrote about the way markets, menús, neighborhood restaurants, and ordinary food infrastructure change what convenience can mean.

But food is only one interface.

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The bread run that disappeared

When I was in high school in Lima, one of the regular morning chores was to go out and buy bread for breakfast.

There was an incentive to go early: the bread was fresh, and if the timing was right, still warm. The outside was crisp enough to crack when you squeezed it, the inside was soft, and the paper bag warmed slightly on the walk home.

I did not think of this as food culture, and I certainly did not think of it as an operating condition. It was just what you did.

The neighborhood baker was part of the morning in the same way the morning was part of the day.

Coming back to Lima now does not restore that life. Some of those old-school panaderías still exist, particularly deeper inside neighborhood life, but they are much less present in the Lima I now move through, and I am no longer the person who left the house in the morning to buy bread.

I learned other shopping patterns elsewhere. For years, I learned to get bread at a supermarket. These days I rarely eat it at all, and when I do crave some, it isn’t for breakfast, so I am much more likely to go to a supermarket than to wake early and search for the freshest batch coming out of a neighborhood oven.

So what exactly changed? Lima? Me? The food system? The neighborhoods I spend time in? The habits other cities trained into me?

All of the above.

That is the problem with simple stories about environment: the environment does not act on a blank person.

We arrive carrying adaptations acquired elsewhere, then encounter a place that has also been changing without us. Cities train people; people leave; other environments train them differently. Eventually they return while the original city has continued evolving in their absence.

This is why going back is never really going back.

Anyone who has returned to a childhood neighborhood, a university town, a former workplace, or a country they once called home probably knows the sensation. The route is still there, but the shop is gone. The smell is familiar, but the ritual is not.

Your body recognizes things that no longer belong to your life, and sometimes fails to retrieve things that once seemed inseparable from who you were.

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The city does not have one speed

There is another simplification worth resisting.

New York is fast.

Málaga is slow.

Lima is chaotic.

Those descriptions are recognizable enough to be useful and crude enough to become misleading almost immediately.

A city does not have one speed. It has thousands of rhythms operating at once: traffic has one, schools another, restaurants another, families another, and financial markets another.

A neighborhood market, an airport, a beach promenade and an emergency room may coexist inside the same municipal boundary while asking entirely different things from the body.

Then there is the person moving between them.

Since coming back to Lima this time, I have noticed that my waking time settled roughly an hour earlier than it ordinarily does in Málaga. I did not decide to become an earlier riser; I simply began waking earlier.

I cannot tell you that Lima caused it because too many variables changed at once. Light exposure changed, household rhythm changed, family life changed, and my own schedule changed. The history I carry here may matter, as may the particular room where I sleep.

That uncertainty is the point.

There is no scientifically clean thing called “Lima” entering my nervous system. There is this organism, in this household, in this part of Lima, during this stage of life, encountering this set of conditions.

Environment is always specific. So is adaptation.

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Activation is not the enemy

Research on urban living makes another easy mistake tempting.

A well-known study published in Nature found differences in neural responses to social-evaluative stress associated with current city living and with urban upbringing. It is an interesting finding precisely because it suggests that the social environment can become visible in how stress is processed.

It does not prove that cities are neurologically bad for us, nor would that conclusion make much sense. Cities also concentrate opportunity, culture, healthcare, education, friendship, novelty, economic activity, and forms of belonging that would be difficult to reproduce elsewhere.

Stimulation is not pathology. Demand is not pathology. Even stress is not automatically pathology.

The relevant question is what the demand develops, what it consumes, and whether there is enough opportunity to return from it.

New York once asked a great deal from me at a time when I wanted much of what the asking produced. That is different from saying the same level of activation should remain desirable forever.

One of the mistakes we make with place is assuming that if an environment helped build us, continuing to fit inside it is proof of strength.

It may simply be proof that we can still tolerate it.

Those are not the same thing.

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When the person changes too

This becomes more obvious across a life.

A city that feels electrifying when someone is beginning a career may feel intrusive when their work already supplies more stimulation than they need. A long commute can be acceptable when it leads somewhere new and intolerable when it has been repeated thousands of times.

Living in the middle of everything can feel like freedom until sleep, children, caregiving, recovery, or the ability to concentrate become more valuable than proximity to everything.

The reverse happens too. A place that once felt boring can later feel spacious, while a quieter environment can initially feel like deprivation to someone accustomed to constant stimulation.

A highly walkable neighborhood can become dramatically more important when driving becomes harder, and proximity to friends, food, healthcare, and ordinary services can acquire a different value when the body no longer treats distance as a negligible cost.

Research on age-friendly environments becomes increasingly explicit about this interaction between person and place. The usefulness of an environment depends not only on its physical features but on how those features meet changing capacities, social conditions and needs.

But we do not need to wait until old age to recognize the principle.

Fit is not a permanent property of a place. It is a relationship. And relationships change when either side changes.

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Málaga is not the answer

It would be convenient at this point to make Málaga the resolution.

I left bigger, faster cities and found the Mediterranean. I walk more, spend time by the sea, and get more sunlight. Food and social contact usually require less planning, while life contains forms of movement that do not need to be scheduled as exercise.

Then we could conclude that slower is better. But I do not believe that.

I can live beside the Mediterranean and spend an entire day staring at a screen. I can have a walkable city and choose not to walk. Someone else can live in exactly the same neighborhood and experience isolation, financial pressure, family strain, or work conditions that make the sea almost irrelevant.

Environment changes probabilities and costs. It does not remove agency, but individual agency does not remove environment either.

This is the part of the argument that interests me most.

The self-improvement version of modern life tends to place enormous responsibility on the individual: improve your habits, protect your sleep, exercise, eat better, manage stress, build community, focus.

All of those things can matter.

But some environments make every one of them another task, while others quietly include some of them in ordinary life.

The deepest effect of a place may not be what it offers. It may be what it makes unnecessary to negotiate.

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What begins as adaptation can look like personality

Stay somewhere long enough and the adaptations become harder to see.

“I walk fast.”

“I hate walking.”

“I need noise to work.”

“I cannot concentrate in cafés.”

“I need to live near everything.”

“I could never live somewhere that quiet.”

“I am not a morning person.”

“I do not know my neighbors.”

Some of those descriptions may be accurate expressions of temperament, but some may also be environmental fluency.

A behavior gets rehearsed because the surroundings repeatedly reward it, require it, or make the alternatives inconvenient. Eventually, the explanation moves inward.

This is just who I am.

I explored a related problem in “The Life You Can Defend”: identities do not live only inside us; they accumulate infrastructure around them.

Place is part of that infrastructure.

A city can retrieve a version of you remarkably quickly. Sometimes that version contains capabilities worth recovering; sometimes it contains a pace you no longer need. Usually it contains both.

That is why I am wary of advice to simply change environments.

Moving can alter the field around a person dramatically, but it can also produce exactly the same life somewhere with better weather.

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The place is part of the system

One of the questions underneath The Human OS Manual is how much of what we interpret as an individual problem is actually being produced, reinforced, or made harder to change by conditions around the individual.

Place makes that question difficult to avoid.

Light, noise, food, movement, work, transport, proximity, relationships and the physical organization of a day do not remain outside the person merely because we call them environment. They become part of what the person repeatedly has to adapt to.

But the answer is not to search for the perfect city.

There is no city without trade-offs, and there is no version of us that remains fixed enough for one set of trade-offs to stay optimal forever.

New York did not betray me by remaining intense.

Lima did not preserve my childhood while I was elsewhere.

Málaga does not owe me permanent coherence because it fits something important in my life now.

Cities change. We change. The relationship has to be read again.

You may not be able to move, or you may not want to. Work, family, money, schools, citizenship, caregiving, community and history make geography far less optional than lifestyle culture sometimes pretends.

But recognizing the environment as part of the system changes the questions available to us:

What does this place make automatic?

What does it make unnecessarily difficult?

What kind of activation does it reward?

Where does recovery happen without having to be defended?

Which parts of me became more capable here?

Which costs became so familiar that I stopped noticing them?

And has the environment that once fit the person I was remained coherent with the life I have now?

My MetroCard did not survive the return to New York. Some of the person who carried it did.

The interesting question is no longer whether I can still move through the city the way I once did.

I can.

It is whether I still need to.

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If this helped you name something you have been feeling but had not quite put into words, please share it with someone who might need the same language.

The Human OS Manual is now available for pre-order. If this work resonates, you can reserve your copy and follow the ideas as they continue to develop.

Feel free to leave a comment. I read and respond to every thoughtful note.

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Notes and sources

• Metropolitan Transportation Authority, “OMNY now available everywhere in Manhattan”.
• James F. Sallis et al., “Physical activity in relation to urban environments in 14 cities worldwide: a cross-sectional study”, The Lancet (2016).
• World Health Organization, “Urban health”.
• Florian Lederbogen et al., “City living and urban upbringing affect neural social stress processing in humans”, Nature (2011).
• Yuxuan Zou, Karina Mak, Wailung Lo, and Min Yang, “What we count shapes what we learn: A systematic review of age-friendly urban environments and later-life well-being”, Health & Place (2026).