We are finally pinning down what makes dyslexic brains different

I used to be stupid. It was a long time ago and I was very young – too young to question teachers who said I was a bit dim. Besides, wasn’t there proof? I had been slow to learn to read, my spelling was atrocious and my aptitude for climbing trees wasn’t fooling anyone. So, I believed them. Then, aged 7, everything changed. For the first time, I had a teacher who saw beyond my literary ineptitude. She told me I was smart – and, suddenly, I was. Thank you, Mrs Kennedy! That was more than 50 years ago. Back then, dyslexia already had a long history, but news of it hadn’t reached the classroom – at least none I found myself in. Children like me usually weren’t given a diagnosis or special help. Far from it. At the convent school I attended next, spelling tests were a ritual humiliation, where the nuns lined us up against a wall in the order of our results and shamed those who failed to perform. Things have changed since then. Teachers are fully aware of dyslexia. Children with this, the most common of learning disabilities, are no longer labelled “stupid” or “lazy”. Huge volumes of research have been published. Yet, fierce disagreements have also raged about what causes dyslexia and how best to diagnose and treat it. Advertisement Now, finally, we are pinning down what makes dyslexic brains different. We may even have found the key neural pathway that drives the condition. Better yet, this research is pointing to novel, practical and fairer ways to help all children who struggle to read. Humans invented writing around 5000 years ago – far too recently to have evolved an adaptation for deciphering the written word. Besides, for most of our history, the vast majority of humanity has been illiterate. So, when we learn to read, our brains must co-opt areas specialised for other functions. That this isn’t straightforward for everyone has long been recognised. The word dyslexia (from the Greek for “disordered words”) was coined in 1883 to describe a curious condition in which experiencing a stroke had left a person unable to read or spell. But, within a few years, it was being used for a far larger group – children who find it hard to acquire these skills. Developmental dyslexia is often described as a significant and persistent difficulty with reading and spelling. Traditionally, the definition has also included the idea that these difficulties are unexpected given the child’s other cognitive abilities – although the recently updated definition issued by the International Dyslexia Association has finally dropped this controversial “discrepancy” idea. We know that both genes and environment play a role, that dyslexia is a spectrum and that it can manifest in different ways, such as spelling difficulties (a particular problem in alphabetic language systems), slow reading and writing speeds, or both. All this makes its prevalence hard to quantify. Most estimates put it at around 10 per cent of people globally; some say twice that. What’s more certain is that dyslexia is a universal human condition found in all languages and writing systems. Reading is cognitively complicated. It entails three key components: understanding how sounds relate to squiggles on a page (phonology); mastering the patterns of written words and the rules of spelling (orthography); and making sense of what you see (semantics). To do this, your brain recruits networks evolved to process vision and speech and links them into a new “reading circuit”. This is located primarily in the brain’s left hemisphere and also comprises three main components. The occipitotemporal region, located low in the back of the brain, instantly recognises those squiggles as words, hence its common name: the “visual word form area”. Word shapes are matched to sounds in the temporoparietal junction, above and behind your left ear. And further forward, the inferior frontal gyrus (Broca’s area) handles speech production and meaning. The underlying circuitry is the same, regardless of the language or script – even for writing systems that don’t look anything alike, such as those for English and Chinese. Clearly, there is a lot that can go wrong, not just in the reading circuit, but in other aspects of reading such as attention, memory, processing speed, logical thinking and knowledge of vocabulary. So perhaps it shouldn’t surprise us that, over the years, researchers have come up with a wide range of ideas to explain the condition. One of the most prominent is the phonological deficit theory, which asserts that the problem lies in poor awareness of speech sounds and difficulty relating these to written symbols. “This is now considered to be a primary deficit,” says Maggie Snowling, a psychologist at the University of Oxford who has long been a proponent of the idea. Phonological deficit and a second problem known as rapid automatised naming (RAN) – slowness in identifying letters, numbers and even pictures – constitute the “double-deficit hypothesis”. Then there are explanations that focus on the brain itself. Temporal processing theory, for instance, points to an underlying problem of timing in the way the auditory system processes sounds, which has profound knock-on effects for reading and writing. The magnocellular hypothesis, in contrast, places an emphasis on visual attention. It stems from findings that magnocellular neurons, which process fast-moving visual information, are less active and less numerous in people with dyslexia. In short, decades of research have generated plenty of ideas, but not much consensus. A major roadblock has been that studies were small and not easily compared. This is now being addressed thanks to the availability of large-scale longitudinal datasets and improved methods. That may not sound dramatic, but it has been a game changer. Take genetics. Clearly, dyslexia runs in families: I have my father to thank for mine. “The heritability you see in twin studies is about 70 per cent,” says Michelle Luciano, who studies behavioural genetics at the University of Edinburgh in the UK. That’s massive – but comes with a big caveat. “It’s not just the genes; it’s the gene-environment correlation that’s really important,” says Snowling. The idea is that factors such as low birth weight and whether literacy is encouraged at home play a key part in shaping the chances of developing dyslexia in those with a genetic susceptibility. There is also no single dyslexia gene – many tiny genetic changes interact to generate the condition in all its guises. And tracking them down is fiendishly difficult. Traditional methods of genetic analysis identified several “candidate” genes that people with dyslexia appear to share. Now, geneticists can scan full genomes looking for variants linked with complex traits – and do this at scale. The first such genome-wide association study (GWAS) on dyslexia was published in 2022. Using information from the 23andMe genetic database, a team led by Luciano analysed the genomes of 51,800 people with a dyslexia diagnosis and over 1 million controls. This revealed something surprising about those previously identified candidate genes. “A lot of these actually haven’t turned out to be that important,” says Luciano. The analysis did, however, identify 42 genetic variants linked with a risk of dyslexia. “Many of these genes had already been reported as being associated with either general cognitive ability or educational attainment,” she says. “But we also found several novel ones that may be more specific to language and reading.” The study highlights the genetic complexity of dyslexia. It also confirms observed links with some neurodevelopmental conditions such as ADHD – but not others. “For autism, for instance, we found no genetic overlap,” says Luciano. She and her colleagues have since worked on an even larger dataset of more than 1.2 million people, identifying a further 13 genes related to dyslexia that implicate early brain developmental processes in the biological underpinning of reading. “Genetic studies give us a possibility to bridge the gap between cognitive theories and neuroscience,” she says. In fact, these genetic findings have already provided a springboard for a giant leap in revealing the neuroanatomy of dyslexia. A team led by Clyde Francks at the Max Planck Institute for Psycholinguistics in Nijmegen, the Netherlands, used them to calculate the genetic predisposition to dyslexia of 35,231 people in the UK Biobank database. They then identified brain regions that differed in people whose genes put them at risk of dyslexia. (I must now declare an interest: I have been in the UK Biobank project from the start, done all the tests and had my genome sequenced and my brain scanned, so one of those 35,231 people is me.) Francks and his colleagues found that the genetic risk of dyslexia was associated with widespread reduction in brain volume compared with people not at genetic risk, especially in language-related and motor areas. (Yikes!) Again, there were correlations with ADHD and other neurodevelopmental conditions – although reductions in the motor cortex were specifically linked with dyslexia. That might seem strange, but motor control could affect reading in a variety of ways, says Francks. “For example, infants with better motor skills might be able to learn language-related skills more quickly through better coordination when producing speech sounds, pointing to track letters and words or keeping time during chants and songs.” Meanwhile, earlier this year, another impressive large-scale study finally nailed a long-standing debate in the field over the contribution of visual difficulties, not just phonological ones, to reading problems. “We and others have long held the view that dyslexia is quite heterogenous, and phonological problems are only one part of the story,” says Jason Yeatman, who specialises in the neurobiology of reading at Stanford University. He and his colleagues carried out tests on 400 children in kindergarten and first grade (typically aged 5-7) at California schools, measuring how quickly they processed visual information such as identifying the direction of dots moving on a computer screen. This revealed that around 15 per cent of the children had problems with visual-spatial attention, and these were associated with reading difficulties a year later. “These kids aren’t picked up by any of the conventional screening processes,” says Yeatman. What’s more, the research identified a hidden subgroup whose weak visual processing was masked by strong phonological skills. But for many people with dyslexia, the primary problem is with phonology and, over the years, researchers have pinpointed a key neurological mechanism underlying these difficulties. It boils down to the way the brain processes the rhythm patterns of speech, in particular the rates of change in loudness that mark the beginning of syllables – a cue that the brain uses to make sense of the stream of information it receives by chunking it into meaningful units. This is the basis of the temporal sampling theory devised by Usha Goswami at the University of Cambridge, which combines phonology with what is happening in the brain. Neurons in the brain fire automatically in response to these sounds, which can be measured using EEG to visualise the brainwaves in the auditory cortex – even in infants who are just learning to speak. “You can think of word representations in the brain almost like auditory objects, like 3D mountains,” says Goswami. However, she and her colleagues have found that children with dyslexia have a subtle mismatch between speech sounds and these mental representations due to problems discerning rhythm and pitch, especially at low frequencies. This doesn’t cause obvious issues with speech, but can have a profound impact on reading and writing, because these skills utilise speech-processing pathways to decode written words. “This really only hits when a child is learning to read,” says Goswami. “The whole shape of the mountain range will be a bit different, but they’re trying to learn to read and spell in a system made for children with another type of mountain range.” For instance, a 2024 study by Goswami and her colleagues of more than 100 English-speaking children in Australia and the UK used EEG to measure their brain responses to speech, and found that issues with temporal sampling were strongly associated with dyslexia. What’s more, this technique could be used as the basis of a ‘classifier’ tool to identify children with the condition. “If we randomly select one child with dyslexia and one without dyslexia, the classifier has a 77 per cent chance of correctly identifying which child is more likely to have dyslexia, based on their brain responses to speech,” says auditory neuroscientist Mahmoud Keshavarzi at the University of Cambridge. Indeed, Goswami thinks that difficulties with temporal sampling are the primary cause of dyslexia, and that the other problems associated with the condition arise during a child’s development. However, other researchers think that the condition is too heterogeneous to be driven by a single underlying factor. “The more recently accepted understanding is that dyslexia is a consequence of multiple biological and environmental risk factors,” says Julian Elliott at Durham University, UK, who researches dyslexia in children. Still, there is clear evidence that boosting the ability of young children to process rhythms can improve their language skills – as demonstrated in a study by Goswami and her colleagues involving 120 children under the age of 11, which added activities such as drumming, chanting and marching to a beat into their classrooms. “These all help stamp in the rhythmic patterns which are so fundamental,” she says. The team is also developing technologies specifically to help those with dyslexia. “We’ve found a neural characteristic called the theta-delta ratio, which is too high in children with dyslexia when they’re listening to natural speech,” says Goswami. One intervention allows children to visualise what is happening in their brain while listening to a story, via the movement of a little spaceship on a screen. “When they’re keeping the spaceship up, it means they’ve reduced their theta-delta ratio,” she says. This feedback leads to improvements in phonology and reading. She isn’t alone in believing we can do more to help children who struggle with reading and spelling. Decades of tinkering make it clear that the key is a focus on phonics – specifically, training on phonemes, letters and single-sound associations, says Snowling. “But it’s also not everything,” says Yeatman. In addition, young readers require help tailored to their particular needs. For those with visual-processing problems, there is no reliable evidence that coloured lenses or special fonts work. But Yeatman’s team has found that this subset of children read faster when the spacing between letters is increased. He also thinks there is potential to train the visual system to work better through specially designed computer games. “This area is ripe for investigation,” he says. Perhaps the biggest thing we can do is identify dyslexia early, as evidence shows that intensive interventions have significant effects on struggling readers, with the greatest influence if these are implemented in a child’s early school years. “I think it’s incredibly important,” says Snowling. Another much-debated area is the best way to test for dyslexia. Assessments typically entail detailed tests, including whether there was a discrepancy between general level of cognitive ability and reading and writing attainment. However, the updated guidelines issued by the International Dyslexia Association have dropped this criterion, not least because it is biased against children from lower socioeconomic groups and those learning to read in a second language. Elliott thinks there is further to go. For years he has been arguing that the terms “dyslexia” be replaced by “reading disability”, so that all children who need help get it. “There are no clear criteria that would enable an assessor to make a determination between a poor reader who gets a dyslexia diagnosis and one who doesn’t,” he says. “Neither is there any intervention suitable for a diagnosed reader that is not equally valuable for any other struggling reader.” His view is controversial, but perhaps that’s not surprising. “It threatens vested interests – a dyslexia industry that is worth billions of dollars,” he says. There are undoubtedly still problems, but progress is being made. “I’m an optimist,” says Yeatman. Me, too. After all, my (admittedly mild) dyslexia hasn’t held me back as a journalist. Today, I have my spellchecker, and eagle-eyed subeditors to pick me up on more subtle slips like “wonton destruction”, which I once used in a quote from an ecologist (and, yes, he was Chinese). But I do think there is still a stigma associated with dyslexia. Otherwise, why would 85 per cent of people diagnosed with the condition not reveal this to their employer? Times have changed, and so should attitudes. So, I’m admitting it here for the first time in my career: My name is Kate Douglas, and I am dyslexic.