Author Annie Dillard wrote that “how we spend our days is, of course, how we spend our lives”. So, how was it that I spent a large portion of my 20s​­ terrified of the big, long life I had before me? After Stanford University, I’d moved to New York to work at Google but I was depressed, anxious.

When I realised that many brilliant and accomplished people were also secretly miserable, just trying to make it through the day, I looked for terminology to describe this, but there was none. So I came up with my own: the underfulfilled overachiever, or UFOA. This describes a constant striver who is living a great‑­on‑­paper life, yet feels disconnected from their work, life and self. UFOAs see success as the organising principle of our lives. We call it by a catchy name: hustle culture. We brag about our intense busyness. Side hustles are a badge of honour. Going “above and beyond” in our jobs is routine. Our primary purpose, unabashedly, is achievement.

Most of us were shaped around expectations from the beginning. We praise kids for being “good students”, by which we don’t mean curious and engaged. We mean high grades and awards. Our education system is built on this principle. This means prioritising productivity – achievement’s codependent ­partner – above almost all else. The central question becomes: “How can I be the most productive today?”

But if this is supposed to guarantee our happiness, why do almost 50% of millennials report symptoms of depression and/or anxiety disorders and ­84% report burnout? And why are these numbers rising? Those are not metrics of success by anyone’s definition. Clearly, our system is broken. The problem is the expectation that with achievement comes fulfilment. It’s not about the most enjoyable way to get to work or being and feeling well during your day; it’s about what each choice can earn you.

The way we’ve been taught to “do” life is all wrong. “Destinational living”, by which we pursue recognisable outcomes based on the lie that these will guarantee security and happiness, is an “end justifies the means” philosophy. Destinational living says: “Decide what you want your life to look like, come up with a 10-​­year plan, and then work backward to determine the most advantageous place to start.” In the abstract, this is a lovely idea. There’s a reason why it’s the dominant cultural paradigm. It’s comforting to believe that the world is so predictable that we can plot it all out in­ advance. If only it were true.

Destinational Living means outsourcing our decision-making. What is impressive, what is ­valuable, is defined not by what matters to us personally but, rather, by what matters to others. In effect, we’re “life plagiarising”. It’s asking, “what did that person do to achieve such success?” and then turning around and saying, “OK, got it. Copy, paste”.

What most UFOAs eventually learn the hard way is that being, or appearing, successful (becoming a CEO, parent, spouse, homeowner) is a different experience from being fulfilled. Fulfilment is a deep sense of belonging to yourself.

Many UFOAs misdiagnose their problem as unreasonable expectations, or workaholism, assuming that they just have to “care less” about work. In 2022, “quiet quitting” –​­ doing the bare minimum required to keep a job – dominated headlines. While I support the sentiment, I’m not a fan of any strategy that is based on engaging less with your life. I’m pretty sure that is not the recipe for fulfilment.

There are also proponents of opting out altogether. There is a movement among young people in China called tang ping, or “lying flat” that is “a way of life [that includes] not getting married, not having children, not buying a house or a car, and refusing to work extra hours or hold a job at all”. I applaud anyone investigating alternative strategies. But ambition is a genuine part of who we are. Not to mention that living antithetically to the cultural system is still living defensively against, instead of for, something.

There’s another way and I call it directional living. Here’s the catch: I can’t find fulfilment for you. The good news is that it’s all up to you. Directional living is like the scientific method but for life. You begin with a ­hypothesis –​­ your best guess as to the direction of a loose “something bigger”. You conduct tests and collect data through your experiences, refining your life hypothesis as you go.

If you have a hypothesis that involves living on the beach, you may test that by renting a house on the coast for one month and collecting data on how right, or not, that is for you. The goal is not to permanently relocate but to find out whether you want to continue exploring that path. Success is in finding what’s true, not in proving your original theory correct.

I’ve found this idea speaks uniquely to UFOAs at this moment in time. The closest thing I have to a personal motto is a quotation that’s widely attributed to Carl Jung but that, as it turns out, he never actually said at all. “The privilege of a lifetime is to become who you truly are.” My greatest hope for you is that you get to live this privilege fully.

Directional Living: Get Unstuck, Find Career Fulfillment and Discover a Life that’s Right for You by Megan Hellerer is out now

• Directional Living by Megan Hellerer (Penguin Books Ltd, £16.99). To support the Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.

Michael Frank has spent his career as an academic researcher working over three decades in a very peculiar niche of computer engineering. According to Frank, that peculiar niche’s time has finally come. “I decided earlier this year that it was the right time to try to commercialize this stuff,” Frank says. In July 2024, he left his position as a senior engineering scientist at Sandia National Laboratories to join a startup, U.S. and U.K.-based Vaire Computing.

Frank argues that it’s the right time to bring his life’s work—called reversible computing—out of academia and into the real world because the computing industry is running out of energy. “We keep getting closer and closer to the end of scaling energy efficiency in conventional chips,” Frank says. According to an IEEE semiconducting industry road map report Frank helped edit, by late in this decade the fundamental energy efficiency of conventional digital logic is going to plateau, and “it’s going to require more unconventional approaches like what we’re pursuing,” he says.

As Moore’s Law stumbles and its energy-themed cousin Koomey’s Law slows, a new paradigm might be necessary to meet the increasing computing demands of today’s world. According to Frank’s research at Sandia, in Albuquerque, reversible computing may offer up to a 4,000x energy-efficiency gain compared to traditional approaches.

“Moore’s Law has kind of collapsed, or it’s really slowed down,” says Erik DeBenedictis, founder of Zettaflops, who isn’t affiliated with Vaire. “Reversible computing is one of just a small number of options for reinvigorating Moore’s Law, or getting some additional improvements in energy efficiency.”

Vaire’s first prototype, expected to be fabricated in the first quarter of 2025, is less ambitious—it is producing a chip that, for the first time, recovers energy used in an arithmetic circuit. The next chip, projected to hit the market in 2027, will be an energy-saving processor specialized for AI inference. The 4,000x energy-efficiency improvement is on Vaire’s road map but probably 10 or 15 years out.

“I feel that the technology has promise,” says Himanshu Thapliyal, associate professor of electrical engineering and computer science at the University of Tennessee, Knoxville, who isn’t affiliated with Vaire. “But there are some challenges also, and hopefully, Vaire Computing will be able to overcome some of the challenges.”

What Is Reversible Computing?

Intuitively, information may seem like an ephemeral, abstract concept. But in 1961, Rolf Landauer at IBM discovered a surprising fact: Erasing a bit of information in a computer necessarily costs energy, which is lost as heat. It occurred to Landauer that if you were to do computation without erasing any information, or “reversibly,” you could, at least theoretically, compute without using any energy at all.

Landauer himself considered the idea impractical. If you were to store every input and intermediate computation result, you would quickly fill up memory with unnecessary data. But Landauer’s successor, IBM’s Charles Bennett, discovered a workaround for this issue. Instead of just storing intermediate results in memory, you could reverse the computation, or “decompute,” once that result was no longer needed. This way, only the original inputs and final result need to be stored.

Take a simple example, such as the exclusive-OR, or XOR gate. Normally, the gate is not reversible—there are two inputs and only one output, and knowing the output doesn’t give you complete information about what the inputs were. The same computation can be done reversibly by adding an extra output, a copy of one of the original inputs. Then, using the two outputs, the original inputs can be recovered in a decomputation step.

A traditional exclusive-OR (XOR) gate is not reversible—you cannot recover the inputs just by knowing the output. Adding an extra output, just a copy of one of the inputs, makes it reversible. Then, the two outputs can be used to “decompute” the XOR gate and recover the inputs, and with it, the energy used in computation.

The idea kept gaining academic traction, and in the 1990s, several students working under MIT’s Thomas Knight embarked on a series of proof-of-principle demonstrations of reversible computing chips. One of these students was Frank. While these demonstrations showed that reversible computation was possible, the wall-plug power usage was not necessarily reduced: Although power was recovered within the circuit itself, it was subsequently lost within the external power supply. That’s the problem that Vaire set out to solve.

Computing Reversibly in CMOS

Landauer’s limit gives a theoretical minimum for how much energy information erasure costs, but there is no maximum. Today’s CMOS implementations use more than a thousand times as much energy to erase a bit than is theoretically possible. That’s mostly because transistors need to maintain high signal energies for reliability, and under normal operation that all gets dissipated as heat.

To avoid this problem, many alternative physical implementations of reversible circuits have been considered, including superconducting computers, molecular machines, and even living cells. However, to make reversible computing practical, Vaire’s team is sticking with conventional CMOS techniques. “Reversible computing is disrupting enough as it is,” says Vaire chief technology officer and cofounder Hannah Earley. “We don’t want to disrupt everything else at the same time.”

To make CMOS play nicely with reversibility, researchers had to come up with clever ways to to recover and recycle this signal energy. “It’s kind of not immediately clear how you make CMOS operate reversibly,” Earley says.

The main way to reduce unnecessary heat generation in transistor use—to operate them adiabatically—is to ramp the control voltage slowly instead of jumping it up or down abruptly. This can be done without adding extra compute time, Earley argues, because currently transistor switching times are kept comparatively slow to avoid generating too much heat. So, you could keep the switching time the same and just change the waveform that does the switching, saving energy. However, adiabatic switching does require something to generate the more complex ramping waveforms.

It still takes energy to flip a bit from 0 to 1, changing the gate voltage on a transistor from its low to high state. The trick is that, as long as you don’t convert energy to heat but store most of it in the transistor itself, you can recover most of that energy during the decomputation step, where any no-longer-needed computation is reversed. The way to recover that energy, Earley explains, is by embedding the whole circuit into a resonator.

A resonator is kind of like a swinging pendulum. If there were no friction from the pendulum’s hinge or the surrounding air, the pendulum would swing forever, going up to the same height with each swing. Here, the swing of the pendulum is a rise and fall in voltage powering the circuit. On each upswing, one computational step is performed. On each downswing, a decomputation is performed, recovering the energy.

In every real implementation, some amount of energy is still lost with each swing, so the pendulum requires some power to keep it going. But Vaire’s approach paves the way to minimizing that friction. Embedding the circuit in a resonator simultaneously creates the more complex waveforms needed for adiabatic transistor switching and provides the mechanism for recovering the saved energy.

The Long Road to Commercial Viability

Although the idea of embedding reversible logic inside a resonator has been developed before, no one has yet built one that integrates the resonator on chip with the computing core. Vaire’s team is hard at work on their first version of this chip. The simplest resonator to implement, and the one the team is tackling first, is an inductive-capacitive (LC) resonator, where the role of the capacitor is played by the whole circuit and an on-chip inductor serves to keep the voltage oscillating.

The chip Vaire plans to send for fabrication in early 2025 will be a reversible adder embedded in an LC resonator. The team is also working on a chip that will perform the multiply-accumulate operation, the basic computation in most machine learning applications. In the following years, Vaire plans to design the first reversible chip specialized for AI inference.

“Some of our early test chips might be lower-end systems, especially power-constrained environments, but not long after that, we’re addressing higher-end markets as well,” Frank says.

LC resonators are the most straightforward way to implement in CMOS, but they come with comparatively low quality factors, meaning the voltage pendulum will run with some friction. The Vaire team is also working on integrating a microelectromechanical systems (MEMS) resonator version, which is much more difficult to integrate on chip but promises much higher quality factors (less friction). Earley expects a MEMS-based resonator to eventually provide 99.97 percent friction-free operation.

Along the way, the team is designing new reversible logic gate architectures and electronic-design-automation tools for reversible computation. “Most of our challenges will be, I think, in custom manufacturing and hetero-integration in order to combine efficient resonator circuits together with the logic in one integrated product,” Frank says.

Earley hopes that these are challenges the company will overcome. “In principle, this allows [us], over the next 10 to 15 years, to get to 4,000x improvement in performance,” she says. “Really it is going to be down to how good a resonator you can get.”

We’re laying out the latest science of what meditation does to your mind. The better we understand the common mechanisms across how different meditation practices affect the mind, the more meditation science can contribute to broader understandings of human psychology.

More relevant for us non-scientists, we’ll get better at developing and fine-tuning styles of practice that can help us get the most out of whatever we’re looking for in taking up meditation. (It’s possible, after all, that there are improvements to be made on the instructions we received a few thousand years ago.)

There’s a lot to get into here, but if you walk away from this with anything, it should be that in the past few years, a breakthrough has begun sweeping across meditation research, delivering science’s first “general theory of meditation.” That means very exciting days — and more to the point, scientifically refined meditation frameworks and practices — are not too far ahead.

Which is great — basic mindfulness practices that help us concentrate on the present are both relaxing and useful. But as psychotherapist Miles Neale, who coined the term “McMindfulness,” writes, if stress relief is all we take meditation to be, it’s “like using a rocket launcher to light a candle.” Some meditation practices can help ease the anxious edges of modern life. Others can change your mind forever.

One way to pursue happiness is to try and fill your experience with things that make you happy — loving relationships, prestige, kittens, whatever. Another is to change the way your mind generates experience in the first place. This is where more advanced meditation focuses. It operates on our deep mental habits so that well-being can more naturally arise in how we experience anything at all, kittens or not.

But the deeper terrain of meditation is often shrouded in hazy platitudes. You may hear that meditation is about “awakening,” “liberation,” or jubilantly realizing the inherent emptiness of all phenomena, at which point you’d be forgiven for tuning out. Descriptions of more advanced meditation often sound … weird, and therefore, inaccessible or irrelevant to most people.

Part of my hope for this course is to change that. Even if you don’t want to join a monastery (I do not), there’s still a huge range of more “advanced meditation” practices to explore that go beyond the mainstream basic mindfulness stuff. Some can feel like melting into “a laser beam of intense tingly pleasurably electricity,” and ultimately change the way you relate to pleasure, like the jhānas. Others, like non-dual practices (which I’ll get into later), can plunge you into strange modes of consciousness full of wonder and insight that you might never have known were there.

Which might leave you wondering why it’s mindful relaxation that gets all the attention. For one thing, there’s how much time we imagine deeper meditation practices will take — we’ll get into that later in this course. Another obstacle blocking advanced meditation’s path into the mainstream is that a critical mass of Americans aren’t exactly itching to become full-on Buddhists. But if you turned to science instead of religion for guidance on these meditation practices in the past few decades, you’d mostly find a bunch of scattered neuroscience jargon that doesn’t all hang together.

Buddhism can paint a really elaborate picture of what’s going on with meditation, with ancient models of meditative development still being used today, like the four-path model. Science has struggled to do the same. We know some interesting but scattered things: Meditation makes parts of your brain grow thicker. It changes patterns of electrical activity in key brain networks. It raises the baseline of gamma wave activity. It shrinks your amygdala.

The problem, as Shamil Chandaria, a senior research fellow at the University of Oxford’s Center for Eudaimonia and Human Flourishing, put it to me, is weaving it all together into a story that shows us the big picture. “In terms of all these neuroscience results,” Chandaria said, “there’s this problem of what does it all mean?”

In a pivotal 2021 paper by cognitive scientists Ruben Laukkonen and Heleen Slagter, that big picture — a model of how meditation affects the mind that can explain the effects of simple breathing practices and the most advanced transformations of consciousness alike — finally began coming together.

Let’s start with plain language. Think of meditation as having four stages of depth, each with a corresponding style of practice: focused attention, open-monitoring, non-dual, and cessation.

Near the surface,“focused attention” practices help settle the mind. By default, our minds are usually snow globes in constant frenzy. Our attention constantly jumps from one flittering speck to the next, and the storm of activity blocks our view of the whole sphere. By focusing attention on an object — the breath, repeating a mantra, the back of your thigh, how a movement feels in the body — we can train the mind to stop getting yanked around. With the mind settled on just one thing, it’s easier to see through the storm.

“Open-monitoring” practices help us get untangled from focusing on any particular thing happening in the mind, opening the aperture of our attention to notice the wider field of awareness that all those thoughts, feelings, and ideas all arise and fall within.

Once you’ve settled the mind and gotten acquainted with the more spacious awareness beneath it, “non-dual” practices help you shift your mental center of gravity so that you identify with that expansive field of awareness itself, rather than everything that arises within it, as we normally do. (I know this probably sounds weird, we’ll get more into it later. Some things in meditation are irreducibly weird, which is part of what makes me think it’s worth paying attention to.)

And finally, for practitioners with serious meditation chops, you can go one step deeper, where even the field of non-dual awareness disappears. If you sink deep enough into the mind, you’ll find that it just extinguishes, like a candle flame blown out by a sudden gust of wind. That can happen for seconds at a time, called nirodhas in Theravada Buddhism, or it can last for days at a time, called nirodha-sammapati, or cessation attainment.

You can think of this progression as four rungs on a ladder that lead from the surface of the mind all the way down to the bottom. Or, from the beginner stages of meditation, all the way through to the very advanced. You can place a huge variety of meditative practices — though not all — somewhere along this spectrum.

And just about everything that’s grown popular under the label of mindfulness is in that first group of focused-attention practices. The idea that meditation can make you “10 percent happier” is talking about these introductory practices that settle the mind.

But the idea that meditation can make you 10 times happier, like meditation teacher Shinzen Young claims, references the next stages: practices that open up once the mind begins to settle.

Now, bear with me. We’re going to retell that story, but using Laukkonen and Slagter’s innovation — the general theory of meditation. The key to this framework is a theory that’s risen to dominate cognitive science in the past decade or so: predictive processing.

Predictive processing says that we don’t experience the world as it is, but as we predict it to be. Our conscious experience is a construction of layered mental habits acquired through past experiences. We don’t see the world through our eye sockets; we don’t hear the world through our ear canals. These all feed information into our brains, which conjure our experience of the world from scratch — like when we dream — only that in waking consciousness, they’re at least trying to match what they whip up in our experience to what might actually be going on in the world outside our skulls.

The building blocks for these conjured models of the world we experience — the predictive mind — are called “priors,” those beliefs or expectations based on the past. Priors run a spectrum from deep and ancestral to superficial and personal.

For example, say you ventured an opinion in front of your third grade class and everyone laughed. You might have formed a prior that assumes sharing your thoughts leads to ridicule. If that experience was particularly meaningful to you, it could embed deep in your predictive mind, shaping your behavior, and even perception of the world, for the rest of your life.

Similarly, our bodies know how to do some of their most basic functions — like maintaining body temperature around 98.6 degrees Fahrenheit — because we’ve inherited priors from our evolutionary history that holding our body in that range will keep us alive. According to predictive processing, consciousness is constructed via this hierarchy of priors like a house of cards.

With all that in place, science’s new meditation story can be put nice and short: Meditation deconstructs the predictive mind.

But hold on. It took billions of years for evolution to slowly, patiently build us these predictive minds. They’re one of the great marvels of biology. Why would we want to deconstruct them?

Well, evolution doesn’t care whether survival feels good. Conscious experience — as we know it — might be a really useful trick for adapting to our environments and achieving the goals that further life’s crusade against entropy and death. But natural selection cares about ensuring our bodies survive, not that we achieve happiness and well-being.

Which is why you often hear meditation teachers talking about “reprogramming” the mind. We don’t want to just leave the predictive mind in pieces. Again, it’s one of the most useful adaptations life on Earth has ever mustered. But in some departments, we might want to kindly thank evolution, while taking the reins and revising a bit of its work to make this whole business of living feel better.

Each step, from focused attention through to cessation, is a deeper deconstruction of the predictive mind. But “deconstructing” doesn’t mean, like, breaking it.

Instead, the key idea is “precision weighting,” which you can think of as the volume knob on each of the priors that make up your predictive mind. The higher the precision — or volume — assigned to something, the more focus your mind pays to it. The more your experience warps around it.

Deconstructing the mind is to progressively turn down the volume on each layer of stacked priors, releasing the grip they ordinarily hold on awareness. By definition, then, the deeper meditation goes, the stranger (as in, further from ordinary) the resulting experience will be.

So let’s go back to our four-step model of meditative depth. We said the first step, focused attention practices, “settle the mind.”

Now, we can say that with a bit more detail. By focusing on one particular thing, like the breath, you’re cranking up the precision weighting assigned to it. You’re holding up the volume knob so that your experience settles around it.

By doing so, you also turn down the volume on everything else. You can see this happen in real time pretty easily — just try picking out one specific thing in your current experience. Like your left earlobe — how does it feel right now?

Really, take five seconds and tune into it.

Looking back, you might notice that the more you tuned into that earlobe, the more everything else began to fade into the background. That helps explain why focused attention practices like basic mindfulness can be so relaxing. You’re turning down the volume on everything that’s stressing you out.

Next, in open-monitoring practices, you drop that object of attention and release the volume knob. But it doesn’t twist back to its normal resting position. Since your focusing practice turned down the volume on everything else, the default setting across your mind at large is now lower.

Focused attention settles your mind onto one object of attention. In open-monitoring, you drop into a more settled mind across the board.

It’s not that you no longer have thoughts springing up. But as those thoughts do, your mind reacts less to them. They’re muted, less sticky, so attention clings to them less. They just come and go more easily.

That’s why during the open-monitoring stage, you begin to see the entire snow globe that mental activity is happening inside of. The idea of a “field” of awareness is no longer a metaphor; you can see it directly.

“Advanced practitioners are said to be able to effortlessly observe experience as a whole,” write Laukkonen and Slagter, without being ‘caught’ by thoughts, emotions, or anything else that arises in one’s sensorium.”

Focused attention practices are an important step in meditation — it helps to calm your mind before trying to see through it. But on their own, they don’t usually lead to big revelations about how your mind works. Open monitoring is where this “seeing through” process really kicks in.

“There is a space of awareness that’s different from the contents of awareness,” said Chandaria, who’s been meditating for about 37 years. “And that’s something that most people aren’t even aware of. The first time we see that, it’s like, oh, I never knew that there was actually an ocean on which these waves were arising. I never knew the ocean.”

As you sink into open-monitoring practice, the predictive mind has loosened its grip on experience. But there are still deep priors at play.

For example, in open-monitoring practice, it probably still feels like there’s a “you” doing the meditating. And that “you” is experiencing “your” awareness. There’s a subject — you — aware of an object, the field of experience.

Non-dual meditation aims at turning down even those deep priors that construct distinctions between subject and object altogether. As well as basically every other possible distinction. During non-dual experiences, there’s no self/other, good/bad, here/there, now/later. All these dualities that underlie ordinary cognition basically melt into a big soup of the Now.

This is the thing — the big soupy Now — that you’ll quickly hear a ton of platitudes about in meditation circles. The illusion of separation, the truth of universal oneness.

That’s because there’s just no great way to describe it — it’s either incredibly weird, or incredibly trite. But if you’re after more descriptions anyway, philosopher and meditator Thomas Metzinger recently published a book containing over 500 different accounts of non-duality, or “minimal phenomenal experience” as he calls it, from advanced meditators across 57 countries. Metzinger is usually at least a decade ahead of the field, so it’s worth a read.

If open-monitoring practice is where meditation’s hefty insights begin kicking into gear, non-duality is where they ramp up. It’s often described as “coming home.” One meditator from Metzinger’s research described it as: “the realization of having finally found home after an eternal search. The pathological searching, the agony of control, comes to an abrupt end, and for the first time you realize what it means to be alive.”

According to Laukkonen and Slagter’s framework, non-duality is the baseline of all experience. It’s always beneath our ordinary experiences — awareness in its least constructed form. Non-dual meditation practice is about “creating the conditions that reduce ordinary cognition that normally ‘hides’ non-dual awareness.”

But even non-duality isn’t the end of the road. It’s still a mode of consciousness. And according to predictive processing, wherever there’s conscious experience, there’s an underlying prior, or expectation, that’s holding it up. This, too, can be deconstructed.

In the past year, meditation researchers have begun to corroborate long-standing claims from Buddhist scripture that if your meditation goes deep enough, the whole show of consciousness can be extinguished — temporarily, that is — altogether.

Nirodha-samāpatti, or “cessation of thought and feeling,” is a summit of meditative attainment in Theravada Buddhism, the oldest surviving form of Buddhism most commonly practiced in Southeast Asia. Cessation is like going under general anesthesia, but without any drugs. Consciousness can be switched off from the inside, for — according to the scriptures — up to seven days at a time (though the first lab data on cessation looked at a more modest 90-minute stretch).

Cessation is a bonafide advanced meditation thing — I’ll make zero effort to convince you it’s accessible to us non-monastic folks. But according to neuroscientist Matthew Sacchet, who leads the Meditation Research Program at Harvard Medical School and Massachusetts General Hospital, the early data collected from studying cessations with neuroscience gizmos supports the idea that meditation deconstructs the predictive mind.

“Cessation could thus reflect a final release of the expectation to be aware or alert,” Luakkonen and Slagter write. It’s like a bottoming-out of the predictive mind.

Coming out of cessation, meditators can observe the reconstruction of the predictive mind, prior by prior. “That puts us in a special state,” Chandaria said. “You can call it reprogramming mode. And in reprogramming mode, we can start to reprogram ourselves in ways that could be more conducive to human flourishing.”

For those of us who aren’t neuroscientists, or don’t care about “predictive processing,” what good does this model of meditation do?

It’s not the objective truth about what meditation actually does. It’s just a story. It’s not comprehensive — there are styles of meditation that wouldn’t fit neatly onto this framework. And meditation doesn’t always follow this trajectory — you can go straight into non-dual practices, or try out open-monitoring before focused attention.

On a personal note, I find this framework really helpful. Immediately after reading Laukkonen and Slagter’s paper, it gave me a way to see my own practice that clicked with my experience better than other stories — which stem from other cultures — about what meditation does.

Now, I usually spend the beginning of my meditation sessions doing focused attention practice to settle the mind. And when I notice my concentration is stable enough, I release the focus and drop into open-monitoring practices. And when my mind falls into an especially weird place that words don’t really capture, I figure, maybe that’s leaning into this non-dual stuff? Just having the labels helped kindle my interest in playing around with things.

And as a scientific framework, this model is generating all sorts of new hypotheses to test. More broadly, it also gives us a way to think through how it’s possible that so many people are trying meditation, but so few are having the big transformative experiences that more advanced practitioners talk about.

Even if some 60 million Americans tried meditation in 2022, if most of them only do some sort of focused attention practice, they’re never trying anything beyond the first step. That’s like concluding that running probably won’t make you significantly healthier because you laced up your sneakers and nothing transformative happened.

When I asked Chandaria how this new scientific model compares to religious models that have been around for ages, like Theravada Buddhism’s four-path model, he said that “Ultimately…all these stories are pointing to the moon. But [contemplative traditions] were pointing with their fingers. Now, we have laser pointers.” And as science progresses, “we’ll be able to work with what we’re finding out about the brain,” he added. “It’s actually about making progress, and by progress, I mean more useful stories.”

The discovery that other vertebrates have healthy, microbial brains is fueling the still controversial possibility that we might have them as well.

Introduction

The human gut microbiome plays a critical role in the body, communicating with the brain and maintaining the immune system through the gut-brain axis. So it isn’t totally far-fetched to suggest that microbes could play an even larger role in our neurobiology.

Fishing for Microbes

For years, Irene Salinas (opens a new tab) has been fascinated by a simple physiological fact: The distance between the nose and the brain is quite small. The evolutionary immunologist, who works at the University of New Mexico, studies mucosal immune systems in fish to better understand how human versions of these systems, such as our intestinal lining and nasal cavity, work. The nose, she knows, is loaded with bacteria, and they’re “really, really close” to the brain — mere millimeters from the olfactory bulb, which processes smell. Salinas has always had a hunch that bacteria might be leaking from the nose into the olfactory bulb. After years of curiosity, she decided to confront her suspicion in her favorite model organisms: fish.

Salinas and her team* started by extracting DNA from the olfactory bulbs of trout and salmon, some caught in the wild and some raised in her lab. They planned to look up the DNA sequences in a database to identify any microbial species.

These kinds of samples, however, are easily contaminated — by bacteria in the lab or from other parts of a fish’s body — which is why scientists have struggled to study this subject effectively. If they did find bacterial DNA in the olfactory bulb, they would have to convince themselves and other researchers that it truly originated in the brain.

To cover their bases, Salinas’ team studied the fishes’ whole-body microbiomes, too. They sampled the rest of the fishes’ brains, guts and blood; they even drained blood from the many capillaries of the brain to make sure that any bacteria they discovered resided in the brain tissue itself.

“We had to go back and redo [the experiments] many, many times just to be sure,” Salinas said. The project took five years — but even in the early days it was clear that the fish brains weren’t barren.

As Salinas expected, the olfactory bulb hosted some bacteria. But she was shocked to see that the rest of the brain had even more. “I thought the other parts of the brain wouldn’t have bacteria,” she said. “But it turned out that my hypothesis was wrong.” The fish brains hosted so much that it took only a few minutes to locate bacterial cells under a microscope. As an additional step, her team confirmed that the microbes were actively living in the brain; they weren’t dormant or dead.

Olm was impressed by their thorough approach. Salinas and her team circled “the same question, from all these different ways, using all these different methods — all of which produced convincing data that there actually are living microbes in the salmon brain,” he said.

But if there are, how did they get there?

Invading the Fortress

Researchers have long been skeptical that the brain could have a microbiome because all vertebrates, including fish, have a blood-brain barrier. These blood vessels and surrounding brain cells are fortified to serve as gatekeepers that allow only some molecules in and out of the brain and keep invaders, especially larger ones like bacteria, out. So Salinas naturally wondered how the brains in her study had been colonized.

By comparing microbial DNA from the brain to that collected from other organs, her lab found a subset of species that didn’t appear elsewhere in the body. Salinas hypothesized that these species may have colonized the fish brains early in their development, before their blood-brain barriers had fully formed. “Early on, anything can go in; it’s a free-for-all,” she said.

But many of the microbial species were also found throughout the body. She suspects that most bacteria in the fishes’ brain microbiomes originated in their blood and guts, and continuously leak into the brain.

“After that first wave of colonization,” she said, “you need to have specific features to go in and out.”

Salinas was able to identify features that let bacteria make the crossing. Some could produce molecules, known as polyamines, that can open and close junctions, which are like little doors in the barrier that allow molecules to pass through. Others could produce molecules that help them evade the body’s immune response or compete with other bacteria.

Salinas even caught a bacterium in the act. Looking under the microscope, she captured an image of a bacterium frozen in time within the blood-brain barrier. “We literally caught it right in the middle of crossing,” she said.

It is possible that the microbes don’t live freely in the brain tissue but are engulfed by immune cells. That would be the “most boring interpretation of this paper,” Olm said, and would suggest that the fish have adapted to bacterial inhabitants by containing them.

However, if the bacteria are free-living, they could be involved in the body’s processes beyond the brain. It’s possible that the microbes actively regulate aspects of the creatures’ physiology, Salinas suggested, the way human gut microbiomes help regulate the digestive and immune systems.

Fish, of course, are not humans, but they allow a fair comparison, Salinas said. And her work suggests that if fish have microbes living in their brains, it’s possible we have them, too.

Impenetrable or Not?

Bacteria have been found living in just about every human organ system, but to many scientists the brain is a step too far. The blood-brain barrier has traditionally been seen as “impenetrable,” said Janosch Heller (opens a new tab), who studies the barrier at Dublin City University and was not involved in the new research. Plus, the brain has immune cells working overtime to zap any potentially harmful invaders. When microbes have been found in the human brain, they are are associated with active infections or typically linked to a breakdown in the barrier due to diseases such as Alzheimer’s.

This assumption was challenged in 2013, when scientists studying the neurological impacts of HIV/AIDS found genetic hints of bacteria in the brains of both sick and healthy people. The findings were the first to suggest (opens a new tab) that maybe humans could have a brain microbiome in the absence of disease.

“No one believed it 10 years ago,” Heller said. Follow-up studies — there haven’t been many — have been inconclusive. “It is very easy to trick yourself into thinking microbes are present because microbial DNA is essentially everywhere,” Olm said. “So it would take a lot of evidence to convince me that it does exist.”

The fish experiment did convince him, and other researchers, that a human brain microbiome is not impossible. What is nearly impossible, however, is confirming that without harming healthy people. To build a case, Link suggested repeating the fish experiment in rodents. “This protocol should be able to be adapted really easily to mouse brains,” Salinas said — and indeed her team has started looking into it. They have found early hints that microbes exist in the olfactory bulbs of healthy mice and, to a lesser extent, throughout the brain.

“There’s no reason, if fish have them, that you wouldn’t have them, or that mice wouldn’t have them,” Link said. If microbes have adapted to cross the fish blood-brain barrier and survive in the fish brain, they could do the same in our bodies. It’s unlikely they would be present at the same levels as they are in fish, he added, “but that doesn’t mean there’s none.”

Even in small numbers, Link said, resident microbes could influence our brain metabolism and immune systems. If they are truly present, this would suggest an extra layer of neurological regulation that we didn’t know existed. We already know that microbes influence our neurobiology: Right now, microbes in your gut are modulating your brain activity through the gut-brain axis by producing metabolites that are sensed by enteric neurons winding through your digestive system.

It’s a fascinating, though unproved, proposition that bacteria in the brain are directly impacting our physiology. However, thanks to research like Salinas’, more scientists are open to the idea that healthy human brains might also be home to microbes.

“Why not?” Heller said. “I’m not shocked anymore that they are there.” The more interesting question, he said, is: “Are they all there for a reason, or are they there by mistake?”

* Update: December 5, 2024
Important contributions to the research were made by Amir Mani, the lead author of the paper.