He mapped the learning brain. Then came the hard part

Stanislas Dehaene enters a small library inside the mansion that houses the French ministry of education. Autumn light filters down from a skylight, illuminating glass-fronted bookshelves holding the journaux officiels – the laws, decrees, regulations and rules of the French Republic. Dehaene takes his place and flips open his laptop as members file in.

As president of the Scientific Council for National Education, a body charged with advising the government on evidence-based learning, Dehaene has a pressing concern: Le Monde has just accused the Council of racism. As he shares this news, the warmth in his voice disappears, replaced by something sharper.

He asks the group to share his rebuttal on social media because Le Monde has declined to print it. ‘I find it ridiculous that we have to waste time responding to such things,’ he says. ‘It’s an accusation completely beside the truth.’

A world-renowned cognitive neuroscientist, Dehaene has published hundreds of refereed journal articles and seven books for general readers on reading, mathematics, consciousness and learning. More than a decade ago, he set out to do something that sounded straightforward: take four decades of research mapping how the brain learns, and compel education systems to follow its insights. He thought the evidence would speak for itself. Instead, he has run into the deeply human resistance of politics, identity and belief. In France, more than one in four children arrive at secondary school without a firm grasp of reading or mathematics. Dehaene does not see these as abstract statistics but rather as the cost children pay for that resistance.

‘It’s been eight years, and the scores of French children are changing a tiny little bit,’ he says with a deep sigh. ‘It’s very, very difficult. The social forces are enormous.’

The previous day, I visited him at his brain-imaging lab, NeuroSpin, in the Parisian suburb of Saclay, where he took me down a hallway known as ‘magnet street’ to the facility’s massive MRI equipment. He paused outside the control room of the newest MRI magnet, an 11.7-tesla scanner, one of the strongest human-rated machines in the world, which displays the brain in finer anatomical detail than ever seen before. A loud mechanical buzz pulsed in the hallway – the vibration of the magnet’s electromagnetic coils. ‘Do you have a pacemaker or anything like that?’ he asked before opening the door.

Inside, researchers huddled around computer screens, and a video monitor displayed a fuzzy image of the tube’s interior. It’s one thing to get adults to lie down in the noisy, claustrophobic setting of an MRI tube, but Dehaene, along with his wife, the paediatrician Ghislaine Dehaene-Lambertz, has worked hard to make children comfortable in this setting.

That instinct to observe a child closely would shape Dehaene’s future work

In one experiment, they put three-month-olds in the tube – the babies had just been fed, wore headphones, and were placed in a specially designed cradle – and played them short sentences, some spoken normally and some played backward, a way to strip out language’s meaning while keeping its raw sound intact. The results, published in Science in 2002, showed that the brain’s architecture for language – the same left-hemisphere regions active in adult brains – was already in place and functioning at three months. ‘Before our work, people barely knew if the cortex was working or not,’ Dehaene says.

He met Ghislaine Lambertz in 1986 while both were working in the lab of Jacques Mehler, a pioneer in cognitive psychology. They became part of a group that met at Mehler’s apartment for dinners of pasta and good wine, and they married within a year – Dehaene laughs while sharing that, a few months after the ceremony, their first son, Guillaume, was born. Dehaene was just 21 and, while he had landed his first job, he still hadn’t defended his dissertation. ‘My son was at my PhD defence,’ he says. ‘So I guess the order is kid, permanent position, PhD.’

After Guillaume, two more sons, David and Olivier, followed. When Olivier was five, his preschool teacher taught him to write his first name, and he proudly signed all of his artwork. Half the time, though, he wrote the letters right to left. The scientist in Dehaene was fascinated; the father was anxious. Was this a sign of incipient dyslexia? Olivier’s backward writing soon disappeared on its own. But that instinct to observe a child closely, to take seriously any unusual turns in their learning behaviour that might signal a problem, would shape Dehaene’s future work.

So would Ghislaine. Over the years, she and Dehaene have built a body of research tracing the brain’s relationship with language from infancy through the first years of reading. Dehaene showed me his wife’s lab, opening a closet where she kept tiny caps fitted with electrodes that could be slipped over a baby’s head to read brainwaves. ‘We divided the field between us,’ he said. ‘You know, she is going to do babies, and I won’t touch it, and I will do adults … but of course we mixed in all sorts of ways until we joined in the middle.’

After the tour, we headed to his office, which holds several 3D-printed models of his brain – including one that lay in a pool of powdery plaster dust, the lasagna-like folds of the cortex fractured. Dehaene told me that a photojournalist had asked him to pose with it, and he stumbled and dropped it. ‘The guy started taking pictures like crazy,’ he says. ‘Well, that was the end of my brain.’

Dehaene often punctuates his thoughts with a high-pitched laugh, eyes sparkling, dimples flashing. The effect is disarming. He turned 61 this May but looks years younger – a lean, agile man with a bald pate and delicate wire-rimmed glasses who sometimes wears a tiny red rosette on his lapel signifying his membership in the French Legion of Honour.

Former students and colleagues call Dehaene a genius. At a recent conference, Andreas Nieder, a German neurobiologist, told the audience: ‘Whenever I talk with him, I have the impression that his brain is ticking along at twice the frequency of mine.’ Later, Ghislaine joked that Dehaene’s productivity suggests that he must have cloned himself. ‘In fact, there are two Stans!’

‘I believe in the expansion of the human mind. I believe this is an extraordinary machine. We should realise its full potential’

Dehaene dismisses such praise. When I ask whether he was simply born with a better brain, his voice softens, and he turns serious – echoing the point he was trying to make in his rebuttal to Le Monde – ‘No, I don’t think so,’ he says. ‘We scan different people, and we see the same circuits … for reading or for mathematics … I’m sure if we dig deeper, we’d find individual differences, but there is a universal organisation. I don’t think I’m different at all in that respect.’

As he has uncovered more and more of the brain’s secrets, Dehaene has developed a deep sense of awe over its capabilities. At the same time, he has become aware of how important it is to nurture those neurons when they are malleable. In his book Seeing the Mind (2023), he describes his delight in watching his four granddaughters develop, knowing that ‘their dendritic trees grow by several billion synapses every day … Their tiny brains are unmatched learning machines.’

That reverence is not without anguish: if a society fails to engage a brain this extraordinary, during the precise window when it matters most – childhood – then it’s condemning a portion of its population to a diminished intellectual life. ‘I believe in the expansion of the human mind,’ Dehaene says, tapping his desk in agitation. ‘I believe this is an extraordinary machine. We should realise its full potential – otherwise it’s a terrible waste.’

Dehaene grew up in Roubaix, a struggling industrial city in northern France, where his father, Philippe Dehaene, a paediatrician, was determined to make up for any deficiencies in the local schools. The elder Dehaene brought home books and magazines akin to Scientific American and National Geographic. He stretched the family budget to buy his sons one of the earliest personal computers, a Tandy TRS-80. ‘It changed my life,’ Dehaene says. ‘I became very active and independent in programming my own stuff, my own games, my own math.’

As a teenager, Dehaene was hired by local families to tutor their children in mathematics. Fractions came easily to him, but the children he helped found them impenetrable. He still wonders what makes some mathematical operations so difficult. ‘We’re still working on it in the lab right now,’ he adds.

His father shaped more than his curiosity. By the mid-1960s, researchers had linked alcohol consumption during pregnancy to physical and cognitive disabilities in infants – something many clinicians dismissed as harmless. By the early 1970s, Philippe Dehaene was studying fetal alcohol syndrome – the world’s leading preventable cause of intellectual disability – and warning the public about it. It was a lesson that would stay with his son: that patiently gathering evidence and stubbornly arguing for it might protect children whom institutions had failed to notice.

After high school, Dehaene won a spot at the elite École normale supérieure in Paris. A few years later, after earning degrees in mathematics and computer science, he realised that, although he loved math, he was particularly interested in figuring out how the brain does math. So he joined Mehler’s lab as a doctoral student, becoming the only cognitive psychology researcher there studying numbers and the brain.

Dehaene found it thrilling to work with two brilliant but opposing thinkers

Susana Franck, who co-edited the journal Cognition with Mehler, recalls messy desks piled with papers and an earnest young man – Dehaene was measuring college students’ reaction times as they chose the higher or lower of two numbers. ‘I have many recollections of being kidnapped into listening to numbers on the loudspeaker of the black computer, and having to say which was the larger or smaller,’ Franck says with a laugh. She and the other subjects easily distinguished numbers far apart, like 1 and 9, but struggled with closer pairs, such as 5 and 6. Even mathematics majors faltered, suggesting the difficulty reflected a structural property of the brain, rather than education.

Dehaene also attended lectures at the Collège de France, the country’s most prestigious research institution. He was particularly drawn to presentations by the neuroscientist Jean-Pierre Changeux, whose bestseller, Neuronal Man (1983), advanced the radical idea that the mind is nothing more than its biology. One day in the lecture hall, someone handed Dehaene a piece of paper on which Changeux had scribbled: ‘Please meet me after class.’ The eminent scientist was looking for a mathematician to create a computer model of how the brain represents numbers. ‘I said yes immediately,’ Dehaene says.

One of the model’s predictions was the existence of neurons that respond to specific numbers, firing robustly for their preferred quantity and less so for numbers further away. This gradient helped explain why Dehaene’s subjects were struggling to distinguish close numbers – a neuron tuned to 5 would also fire somewhat strongly for 4 and 6, less so for 1 or 9. (Fifteen years later, Nieder tested the theory in monkeys and found exactly what the model predicted.)

Dehaene found it thrilling to work with two brilliant but opposing thinkers. Mehler favoured studying behaviour to infer how the brain produces thought; Changeux argued for mapping neurons directly. ‘They disagreed about everything,’ Dehaene says. ‘And I was in the middle.’ He decided he must somehow combine both.

A cartoon adorns Dehaene’s office door (The brain cannot do two things at once.)

The resolution came in 1988 as he was flipping through Nature and came upon a study by American researchers who had used PET scans to track changes in cerebral blood flow while patients listened to or read single words. He snapped to attention: the article described how scientists had watched a proxy for thought flicker across a living brain.

‘You know how people have flashbulb memories?’ he says. ‘I have one of reading that paper – I can almost see the journal and where I was sitting.’

Dehaene soon decamped to the University of Oregon for a postdoc with Michael Posner, one of the Nature paper’s authors. Dehaene spent two years there learning to combine brain scanning – which in those days required injecting the patient with a radioactive tracer – with behavioural experiments.

In 1994, he moved back to Paris, eager to return to number research. There, he continued his collaboration with Laurent Cohen, a colleague from Mehler’s lab, who had access to patients with brain lesions that affected their number perception. Some could read the symbol ‘7’ but had no sense of its quantity. Others could estimate ‘about 7’ when shown a cluster of dots, but couldn’t recall the answer to a problem like 7 × 8 = 56. The two researchers concluded that the brain contains three separate but interconnected number systems: one for visual symbols, one for words, and one for approximate quantities.

Children counting on fingers is in fact a scaffold to the abstract, not a crutch

One of those patients, whom Dehaene later described as ‘Mr N’, had a lesion in the back of his left hemisphere that had wiped out his ability to calculate exactly – but left his sense of approximation intact. Ask him how long a quarter of an hour is, and he’d say ‘10 minutes’. How many days are in January? ‘15 or 20.’ A dozen eggs? ‘Six or 10.’ He’d lost the symbols but kept the feel of the numbers.

Dehaene furthered the lesion work with brain scanning to show that exact calculation (which involves both symbols and words) and approximation (which does not) rely on separate neural circuits. He then theorised that the brain contains an evolutionarily conserved area specifically for approximation: what your brain automatically does when you glance at the carrots in your crisper drawer and estimate six – you might be off by one or two, but you have a general sense of the quantity without counting them.

In his early 30s, Dehaene was already thinking about writing about this research for a general audience. An avid reader – Vladimir Nabokov is a favourite – he dreamed of a bestseller that would boost his academic salary and reputation, the way The Language Instinct (1994) had done for Steven Pinker, whose research had parallels to his own. ‘It’s one of these books where you laugh out loud,’ Dehaene says, ‘because he has jokes, he has great puns – but at the same time he’s conveying very good science.’

Dehaene’s book The Number Sense: How the Mind Creates Mathematics (1997) did not become a bestseller, but it earned strong critical acclaim, a New Yorker profile, and a $1 million grant – and established Dehaene as a leader in the new field of number cognition.

The research also unleashed something beyond scientific ambition. In the book, he argues that children who can’t grasp fractions aren’t slow or incurious – rather, schools were squandering the numerical abilities children naturally bring to the classroom. Teachers forced abstraction too soon, handing out symbol-only worksheets before children had built the mental models to support them, and discouraged children from counting on fingers, when in fact it’s a scaffold to the abstract, not a crutch.

‘Despising children’s precocious abilities can have a disastrous effect on their subsequent opinion of mathematics,’ he wrote in The Number Sense. ‘It [fosters] the idea that mathematics is an arid domain, detached from intuition and ruled by arbitrariness.’

Afew years later, having tackled numbers, Dehaene turned to reading. In his book Reading in the Brain (2009), he describes how he and Cohen mapped the neural circuits that recognise written letters – a region he nicknamed the ‘letterbox’ – and showed how these connect to networks that process speech sounds. Dehaene and the psychologist José Morais would soon scan unschooled, illiterate adults from Portugal and Brazil to see what the letterbox region looked like when compared with that of literate adults. The answer was stark: a markedly diminished response to written words.

Dehaene was unsettled by the fact that those subjects were socially fluent, verbally intelligent people, and yet some couldn’t follow instructions that most children manage easily. In Brazil, for example, he tested a hospital employee who couldn’t accept that a letter and its mirror image were different symbols – p versus q – insisting on igual (‘the same’) – for every pair. In Portugal, he worked with ‘a lovely woman’ who spent 10 minutes trying to understand a task that asked only whether two pictures matched. ‘The loss of human potential,’ he wrote to me in an email, ‘and also their own feeling of inferiority, of lack of confidence, or sudden realisation that they couldn’t do it – did make me sad.’

For Dehaene, what was at stake was whether a human being would ever gain full access to their own mind. His research indicated that systematically learning letter-sound relationships – which is what phonics curricula do – was the best way to develop the reading circuit and turn on the letterbox. Yet most schools were not teaching phonics strictly. Instead, they were using variations of ‘whole language’ – which rose to prominence in the 1970s and ’80s – and was built on the false belief that reading is a natural skill acquired through immersion. Whole-language curricula encouraged students to infer words from context and memorise shapes.

Brain-imaging data tipped the evidence further toward phonics, and he was ready to fight

In California, the adoption of whole language in the late 1980s had resulted in plummeting reading scores. Rather than eliminating it, the state, along with many other school systems in the US, France and other countries, allowed teachers to combine the two approaches in what became known as the ‘mixed method’ approach.

But now, in the mid-2000s, Dehaene had brain-imaging data that tipped the evidence further toward phonics, and he was ready to fight. At the Collège de France, where a chair had recently been created especially for him, he organised a symposium on the science of reading. He began giving speeches, writing op-eds and going on the radio. He confided to friends that he wanted his findings to reach beyond scientific circles. Elizabeth Spelke, a Harvard psychologist and colleague who now serves on the Council, remembers when he first shared that ambition. ‘I thought: “Poor Stan, that is a hopeless task.” Dehaene, she knew, was bound to face resistance ‘from teachers, from parents who worry you’re using their child as a guinea pig.’

A further trigger for his outspokenness was a report by the sociologist Jérôme Deauvieau on what was actually happening in Paris’s schools. Deauvieau had spent time in first-grade classrooms in the city’s impoverished banlieues, where many children are the sons and daughters of immigrants from North and West Africa, often the first in their families to be educated in French.

The kids sat one by one with a researcher, reading aloud from a simple story about a hen and a dove. A third of the children read fewer than 30 to 40 words per minute – some fewer than eight. They skipped words, mispronounced others and guessed from context, rather than sounding out the words. Deauvieau’s report found that only 4 per cent of the teachers used systematic phonics, while 77 per cent used mixed methods.

Those observations confirmed Dehaene’s worst fears, and he dashed off a piece to Le Monde. ‘Their school hell is paved with good pedagogical intentions,’ he wrote. He pointed out that 20 per cent of students taught this way struggled with literacy, and they were disproportionately from low socioeconomic backgrounds. ‘The others succeed,’ he noted, ‘because their families compensate, as best they can, for the deficiencies of the school.’

On the same day as the Council session, I attended a less formal meeting where researchers and ministry staff were reviewing recent third- and fourth-grade math scores. On one side sat several young researchers; on the other was Dehaene, using the brim of his black fedora to prop up his phone so he could keep track of his messages. (When I mentioned the fedora, he joked: ‘It’s for protection. People with hair don’t understand!’)

He was focused on a large video screen revealing page after page of disappointing results, murmuring ‘stupéfiant’ and ‘tout à fait inacceptable’. The data showed third-graders struggling with simple addition and subtraction – many couldn’t add 25 + 25. ‘This confirms what we all know,’ Dehaene said at last, ‘which is that the decline in math skills is catastrophic. But it’s not just about speed or memory. In my opinion, it’s much more about the very meaning of what we’re doing in these operations.’

Later, he turned to me, shook his head, and said softly: ‘They want pedagogical freedom, but look at the results.’

The backlash began soon after the Scientific Council was created in 2018 by the French president Emmanuel Macron’s first education minister, Jean-Michel Blanquer, who chose Dehaene to be its leader. The education establishment saw the move as science being recruited to override professional judgment. The teachers’ unions declared that ‘no discipline can legitimately impose itself on others.’ A kindergarten teacher, speaking to a reporter, put it more plainly: ‘You can’t transpose what happens under a microscope and ignore the learning conditions. Has the child eaten well? Slept well? Does he or she feel safe?’

When the ministry issued a Council-influenced guide on reading through phonics, the unions compared it to Mao’s Little Red Book. An esteemed psychiatrist went further, accusing Dehaene of imposing a neuroscience-first view that located children’s learning difficulties in their brains rather than in their psychological, family or social context. ‘C’est de l’eugénisme!’ he declared in Le Point.

‘This political debate surprises me,’ Dehaene said in an interview with Le Figaro in 2018. ‘I am neither Left-wing nor Right-wing. I am a scientist.’ He was also, he insisted, not the cold reductionist his critics described. He was soon to publish his next book, How We Learn (2020), which opened not with a brain scan but with the story of a seven-year-old Brazilian boy who had been shot and left blind with limited motor skills, yet spoke three languages and wrote imaginative stories. In the opening sentence of this book, Dehaene wrote that ‘an extraordinary child forced me to drastically revise my ideas about learning.’

Why would a famous brain-scanning scientist want to do fieldwork in the classroom?

Despite the Council’s contentious start, Dehaene endured. He and Cassandra Potier Watkins, one of his researchers, founded a nonprofit called Excello to develop evidence-based curricula and test them on real students. Their first project was Kalulu, a tablet-based app designed to teach beginning readers letter-sound relationships.

Potier Watkins led a randomised controlled study for Kalulu in 2023, and one day she visited a school where two young teachers, short on funds, had downloaded a whole language reading program from the internet. ‘Words’ appeared on screen as strings of shapes – circles, rectangles, squares – separated by occasional punctuation. The children were supposed to say what they noticed. They stared at the screen, confused. ‘It was the dumbest thing I had ever seen,’ says Potier Watkins.

Later, Dehaene had those teachers give their students reading instruction using Kalulu. The study results showed strong gains among kindergarteners that persisted into first grade but faded by mid-year – likely because the app’s phonics instruction was disconnected from actual classroom practice. So the Excello team expanded it into a fuller curriculum, including reading booklets and card games for group play. Meanwhile, a more recent randomised controlled study in Brazil – not yet peer-reviewed – compared 701 first-graders using Kalulu with 414 peers receiving standard instruction. By the year’s end, the Kalulu group’s fluency was about 50 per cent higher.

Potier Watkins discovered Dehaene’s work as a young mother, reading his books before returning to school herself for a degree in cognitive science. When she told colleagues she hoped to do her PhD under Dehaene, they were dubious – why would a famous brain-scanning scientist want to do fieldwork in the classroom? ‘I did not fret,’ she says. ‘I had read Stan’s books, where he said the classroom should be our next laboratory.’

When I was interviewing Dehaene at NeuroSpin, he asked if he might check his phone. Since Blanquer stepped down in 2022, there has been a revolving door of education ministers, and Dehaene had heard that the current one would be reappointed, but he wanted to make sure. ‘Do you mind?’ he asked, swiping the screen. In fact, she’d just announced her resignation. ‘Voilà, démission,’ he said, throwing up one hand. ‘My goodness,’ he added softly. ‘I don’t even understand.’

There have been eight ministers since the Council was formed, and Dehaene is often the one who meets with the newest officeholder to bring them up to speed.

‘I get very passionate when I see a beautiful problem, and I think I have a bit of a solution,’ he says. ‘So that’s for science. But for education, it’s also the indignation of thinking that we have all this knowledge – we’re in the 21st century – and we can still have children who fail because of stupid, inappropriate education.’

That tension was on display the very next day at the meeting in the ministry library, where Dehaene discussed the accusations in Le Monde. The journalist, Stéphane Foucart, saw equivalent danger in a Council report invoking genetics as one source of individual learning differences and Donald Trump’s claim that criminality is ‘in [immigrants’] genes’.

The article’s premise felt clickbaity to me, but Dehaene had taken it seriously. In his rebuttal, he pointed out that some pupils do struggle because of disorders with a partially genetic origin – dyslexia, autism, deafness. Foucart had it backward, he added, and the Council’s position was the opposite of fatalistic; yes, teachers should be aware of these disorders, but that doesn’t mean a child’s genes set fixed limits, and the research is clear – all children can progress.

The rebuttal could make Dehaene sound like someone arguing only from the numbers, batting away a non-scientist’s analogy. But back at NeuroSpin, as our interview was wrapping up, he told me that something beyond data drove him. ‘I just love children,’ he said. ‘People are surprised by that. They think of me as a mathematician or something, but when I see a baby, I melt.’