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Nazareth Castellanos, neuroscientist: ‘We need to teach anxiety prevention techniques from school onwards’
The researcher has dedicated the last 20 years to studying the impact of breathing on the brain
Madrid – DEC 26, 2025 – 21:28 CET
She arrives at our meeting like a ray of sunshine. Vital, cheerful, and kind, Nazareth Castellanos, 48, runs a laboratory where she researches the neuroscience of meditation and the relationship between the brain and the rest of the body. A few months ago, she published the highly successful book El puente donde habitan las mariposas (The Bridge Where Butterflies Live), which discusses how — with “willpower and a lot of effort” — we can sculpt the brain through breathing.
Drawing on the work of Santiago Ramón y Cajal, the father of neuroscience, and Martin Heidegger’s essay Building, Dwelling, Thinking, Castellanos suggests that we shape ourselves by protecting our own growth, that we truly “dwell” when we learn to take care of ourselves, and that thinking begins with gratitude. This requires cultivating an inner dialogue that strengthens rather than harms us — letting go of what is damaging, refining our thoughts, and practicing self-compassion. Through conscious breathing, she argues, we can even sculpt the brain.
Question. Your book is a tribute to Santiago Ramón y Cajal, and cites one of his famous sayings: “Every man can be, if he sets his mind to it, a sculptor of his own brain.” Where do we begin?
Answer: Well, we can all achieve it, but not all of us set our minds to it. The book stems from that reflection: why some people shy away from the idea of sculpting their brains, which for me is one of the biggest problems we have in society. We have seriously neglected mental health, and I think it’s time to overcome that blindness. There’s an invisibility surrounding mental illness that generates a lot of suffering that could be avoided. There’s a concept in medicine that fascinates me: avoidable suffering. It’s the kind of suffering that technology or medicine aims to reduce, just as pain is reduced by inventing a drug. Medicine works to prevent this avoidable suffering; however, there’s no such concept applied to mental health. That’s where we need to focus our attention.
Q. You’re a neuroscientist and have spent more than two decades studying the impact of breathing on the mind. How does science approach something as automatic as breathing?
A. My interest arose when I was working at King’s College London on a project about childhood brain injury and its aftereffects. At that point in my life, I had a reflection that made me question science. I wondered why the science to which I dedicated so many hours wasn’t teaching me anything about myself. Why couldn’t I apply all that knowledge I had about the brain to my daily life? Sometimes I felt lost and didn’t understand how it was possible that I, who studied the brain, couldn’t apply what I researched to myself. After analyzing it, I came to the conclusion that it was easier to access the brain through the body than through the mind. I wanted a more practical, more accessible neuroscience. I already meditated, I knew different meditation techniques, and I wanted to connect them with science.
In Europe, there was a movement proposing to study the influence of the body on the brain, and I joined that movement. I left the project at the University of London and returned to Spain to start another one on brain-body interaction at the Complutense University of Madrid. It was a very risky project; there was no scientific evidence, and it was funded with private resources. It has been a self-funded, long, and slow investigation, but also one with a freedom that I value immensely. Being able to decide which questions we addressed and how we addressed them, always following the scientific method, but without pressure. That freedom is wonderful; I wouldn’t trade it for anything.
Q. What does the title of your book, The Bridge Where Butterflies Live, allude to? What is that bridge?
A. I wanted a poetic title, since it deals with something very personal to me, and I wanted to avoid the technical. We talked a lot about the plasticity of the brain, about bridges. Martin Heidegger says that “the bridge is a place,” synonymous with being present. Dwelling in it is the central theme that occupies Heidegger and that occupies me. And the butterflies refer to the mysterious “butterflies of the soul,” as Ramón y Cajal called neurons. Butterflies whose wingbeats — who knows — may one day reveal the secrets of the mind.
Q. Heidegger plays a key role in your theory. How did you come to him?
A. Out of curiosity. I was invited to a conference at the College of Technical Architects in Madrid, where they discussed the influence of architecture on our psyche, how the environment influences us. There, they mentioned Heidegger’s book, Building, Dwelling, Thinking, which captivated me. As soon as I left, I ordered the book, a small volume that engrossed me in months of reading, because Heidegger is very dense and condenses immense wisdom into every sentence. It’s been my companion for over a year; I’ve read and reread it…
Q. Heidegger also says we are islands connected by bridges. Do you agree?
A. Absolutely, it’s an idea that has helped me a lot. The bridge is a place. It’s neither you nor me, it’s the interaction between us right now. From a bodily point of view, when there is synchronization between two bodies, it’s not my heart nor yours, not your brain nor mine… They both enter into a dance, they reach an agreement. To agree is to put hearts in sync. I find that idea of interaction very beautiful. He also said something that helped me understand many situations: we are two islands, from which shore of my island does the bridge that connects me to you emerge? There are shores that may be wounded and not be the best place to connect. This led me to consider from where I relate to others. Heidegger argues that the moment a bridge appears, a stretch of coastline emerges that you may not have known existed. I thought it was brilliant.
Q. How does Heidegger complement Ramón y Cajal, the father of neuroscience in Spain?
A. I think in many ways. For example, in the idea of serenity, what Heidegger calls gelassenheit. I strive for serenity during fierce storms and also when things are going well. I believe in experiencing joy and fulfillment from that serenity, and also pain. That’s where true strength lies, because without that calm, one reaches enormous levels of misery. Cajal also experienced the gelassenheit that Heidegger spoke of. Cajal had a difficult life, but he found refuge in painting, which allowed him to return to himself, find calm, and strengthen his will. I believe in that calm, which we study through conscious breathing. Calm is neither verbal nor analytical. It’s about inhabiting, being present. Living in the moment, which can sometimes be very hard. There are situations that surpass understanding, and all that remains is to inhabit them. I like that gelassenheit, which translates as being here, being present, being equanimous… It’s not at all analytical.
Q. How does neuronal architecture get reshaped through willpower? Why is breathing such a fundamental tool?
A. When the brain has to rebuild itself, one of the structures most involved in its reorganization is the anterior cingulate cortex, which divides the deeper and more superficial parts of the brain — that is, the unconscious from the conscious. It’s a kind of switch, a fascinating structure. Studies show that this area is activated in many ways and is involved in many processes. Simply by observing your breathing, even without changing the rhythm or breathing patterns, this area of the brain registers significantly more activity than if you’re thinking about something else.
By observing the breath, the brain recognizes that what you’re observing is an interoceptive process [the ability to interpret internal signals from your own body], which triggers immense neural activity. The project I started here was to see what happens in the brain with moderate meditation. I wanted to study something I could do, like meditating for half an hour a day, and maybe not every day.
Q. What conclusions have you reached through meditation?
A. Meditation is intrinsic to human beings. It’s not a technique invented by Buddhism; it’s present in all traditions. It’s contemplation. I see it as more of a human trait than a cultural one. It’s a very valuable tool that you can use even if you don’t meditate regularly. Ideally, according to studies, you should meditate regularly at least five days a week for a minimum of half an hour. We’ve worked with people we teach to meditate, to see what happens in their brains. At the end of the program, which lasts eight weeks, the vast majority don’t continue meditating, but the benefit is that they’ve learned strategies they can use at different times. Those who continue meditating experience many more benefits, as they create a much more stable baseline state. Those who don’t can at least resort to this technique at certain times.
Q. Should we all learn to breathe consciously?
A. It really frustrates me that these techniques aren’t taught in school. We learn very complex things, but not these kinds of techniques. I learned to relate to my own emotions when I was in my thirties, and that’s because this is what I do for a living. A wandering breath leads to a wandering mind. Observing your breath helps maintain serenity. It’s scientifically proven and is a great tool against suffering. To reduce the body’s response to anxiety, you have to breathe, as orderly as possible, so the brain has one less stressor. I wonder how much suffering we could have avoided.
Q. In correspondence between Heidegger and Hannah Arendt, he recommends inhaling while counting to three and exhaling slowly to six. Is that meditation?
A. That’s the most basic process of slowing down breathing, the one that has been most scientifically studied. We tested it on a population with chronic pain from discopathy. We wanted to see not only how it influenced inflammatory factors, but also their experience of living with the pain day after day. When we inhale, the brain is oxygenated and certain areas are activated, and when we exhale, they are deactivated. The brain is like an airplane; it ascends very quickly and takes much longer to descend. Normally, we make the exhalation very short, interrupting the process, without allowing time for those areas to deactivate, which is fundamental. Researchers at the University of Tokyo demonstrated that when the exhalation is longer than the inhalation, the amygdala, which is the area of the brain most involved in emotion and anxiety, relaxes sufficiently, resulting in a less exaggerated response to anxiety. This slowing down, in addition to certain cardiovascular benefits, has analgesic properties, which is why we study it for chronic pain. It also has a calming effect. You should try to breathe slowly.
Q. What you’re proposing seems valid for mature minds. How can we reach younger generations?
A. We need to educate children in anxiety prevention techniques from school onwards. We suffer from a very serious mental health problem. There is enough scientific evidence to recommend including content on body awareness and relaxation techniques in the curriculum. It is a matter of public health. There are enormous levels of suffering, dissociation, and disturbance that are invisible and embedded in society.
Q. How can we make this apparent to people in their twenties, who are already out of school?
A. I see that they’re very demanding of new things. I’m worried about young people’s dependence on social media, which makes them disconnect from being present, from communicating. They’ve found themselves with a new toy that’s very dangerous. Social media often creates a distorted or false sense of reality. I’ve experienced it myself. People tell me, “Wow, you never stop!” — but that’s not true. I spend almost every afternoon with my daughter, yet from what’s posted on social media it looks like I’m constantly busy, even though I advocate for rest. Everyone appears perfect on social media, which isn’t true. That’s worrying to me. I think we should promote humility and simplicity. I’m optimistic because it seems to me that schools are increasingly adopting approaches to address these new realities. We’re on the right track, although there’s still a lot to be done.
Q. So how can we help young people stimulate cognitive development, curiosity, and enthusiasm?
A. I think we’re already doing it. Personally, I’d rather live in 2025 than in the 1970s. There has never been so much access to knowledge or so much curiosity. Very few people studied before, and yet the amount of information we have at our fingertips today is incredible. You just have to know how to search; that’s the problem now. Because, who can I trust? I’m a big advocate for science communication because, being illiterate when it comes to technical terms, it’s very easy to be taken in. Education gives you that ability to discern. A Facebook page uses artificial intelligence to make videos of me and dubs my voice saying utter nonsense. You wouldn’t believe the number of messages I get from people asking if it’s really me. It makes me happy because it means there are already people with enough education to understand that some messages sound unbelievable. We have to keep working, but I’m very optimistic.
Q. You claim that 70% of European society is exhausted. How should we interpret this?
A. Exhaustion is an underestimated issue that no one seems to care about or address. We study it extensively in the lab. Seventy percent of people are exhausted, and among mothers, the figure rises to over 80%. I often see a habit among my friends, one I’ve also fallen into, which is using the TV as a babysitter for the children. We study the impact of overexposure to screens on children extensively, but the problem is that perhaps that mother simply can’t take it anymore. We should be taking much better care of ourselves.
Q. If society took better care of us and we took better care of ourselves, could we reverse that exhaustion?
A. I now put my eight-year-old daughter first. But I’m aware that if I don’t take care of myself, everything will fall apart. When I’m not looking after her, I feel terrible, and I’m barely able to delegate. But if I don’t take care of myself, I can’t take care of her every day.
Q. How can we begin to cultivate our brains so that we understand the importance of self-care? What kind of inner monologue do you propose?
A. [The priest and writer] Pablo D’Ors says something very beautiful: “How can you know yourself if you don’t love yourself?” What good is self-knowledge if it’s not for self-care? Before you know yourself, you have to take care of yourself, as Heidegger says, and when I do know myself, it will be to take better care of myself. We must always maintain that dual perspective.
Q. Is it necessary to verbalize our worries constantly?
A. When my daughter was born, I was exhausted because I was taking care of her all day and working at night. I spent the whole day saying, “I’m exhausted!” And I read articles that showed that exhaustion increases if you verbalize it. We underestimate the power of language; the act of verbalizing activates brain mechanisms that can be toxic. Language isn’t just about what we say outwardly. We pay a very high price for language, which is why knowing how to listen is just as important as knowing when to be silent. When you breathe consciously, the areas of the brain that govern language lose neural resources. This is the key to the mantra effect being studied at Tel Aviv University.
Researchers have shown that when inner dialogue becomes overwhelming or obsessive, and you can’t stop ruminating on something, stress levels skyrocket. Since the brain needs language, they proposed giving it language but not content. It’s necessary to repeatedly use a neutral word that has no religious or motivational significance. For example, “glass.” When anxiety spikes, repeating this word keeps the language areas active but interrupts the connection to the emotional area, thus reducing the anxiety-inducing spiral. The mantra effect also has a unique characteristic related to breathing, which is what religious prayers, for example, have always done: if you repeat a word over and over, you induce a regular, periodic breathing rhythm that modulates respiration. It’s a very powerful technique for controlling anxiety.
Q. You advocate practicing kindness and courtesy as tools for all these processes. Why?
A. Kindness greatly changes the experience. Kindness is the way you look at things, not what is being seen. The same thing said in one way or another generates very different reactions. In legal proceedings, before going to court, a mediator is considered. I think it’s a very useful tool; it reduces hostility in how things are said.
Q. Another brilliant line from your book is “Tenderness is more important than intelligence.”
A. I think they’re linked, although I also believe that to be tender, you have to think. Because tenderness is one thing, and sentimentality is another. Tenderness isn’t just how you say something; it’s understanding the other person, it’s your attitude. Eugenio Borgna, one of the great Italian doctors who humanized psychiatry and advocated for the closure of psychiatric hospitals, says that tenderness is making the other person feel deserving of the life they inhabit.
Q. If we change our minds, do we also change our lives?
A. Not life itself, but our position in life. Sculpting our minds can lead us to discover another person within ourselves. It requires courage, dedication, and confidence. It’s also important to have resources that not everyone possesses, such as financial or cognitive resources, a support network… Circumstances play a significant role, which is why we must continue to support women’s economic, cognitive, and emotional independence. There is still much to be done. To quote Ortega y Gasset: “I am myself and my circumstances.” You can’t achieve it simply by wanting to. It requires intention, and also the right conditions.
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