Winter 2023

Dyslexia and the Developing Brain

Research on dyslexia is identifying the many factors — neural to societal — that are linked to the condition

December 2023

  • by Molly McDonough
  • 8 minute read

Roberto Olivardia

As a child, Roberto Olivardia didn’t enjoy reading. Processing the words on a page fatigued him. But Olivardia — now a psychologist at McLean Hospital and a lecturer at Harvard Medical School — never considered that he might have dyslexia. He remembers watching an episode of the ABC Afterschool Specials series about a boy with dyslexia who wrote words backwards. Since Olivardia’s writing looked normal, he thought “that’s not me.

Decades later, Olivardia witnessed his six-year-old son experiencing a similar fatigue. Only the six-year-old’s was worse. “His vocabulary was off the charts, it was so extensive,” Olivardia recalls, “but with reading, there was a real difference between him and other kids.” Only after his son’s diagnosis of dyslexia did Olivardia become aware of the condition’s complexities: how misunderstood it is among parents, teachers, and doctors; how it manifests in myriad ways; and how a diagnosis can change everything.

The road to diagnosis

Yet getting that diagnosis is not always easy because physicians and scientists are still putting together the many puzzle pieces of dyslexia, a language-based learning disability that affects an estimated 7 to 10 percent of the population. The condition is marked by a person’s difficulty to accurately and fluently read words and to accurately decode and spell words.

Although the causes for dyslexia are complex, a main factor is a person’s difficulty with phonological and phonemic awareness; that is, their ability to recognize and manipulate the spoken parts of words, which sets the stage for decoding, blending, and, ultimately, reading words. Imagine, for example, being presented a word from a language other than your native language, written using symbols or an alphabet associated with that language. It may be possible to get a sense of the sounds in the word — but remembering all of them and blending them together could be hard. Each letter would need to be deciphered, and their sounds stitched together to form a word. It’s a process that can take time.

Doctors in Europe began talking about dyslexia in the nineteenth century — around the time compulsory schooling became more common. They described a curious paradox: cases of individuals who, despite being otherwise healthy, had trouble reading. In 1896 in the British Medical Journal, physician William Pringle Morgan wrote about a 14-year-old patient who he described as a bright and intelligent boy whose “great difficulty has always been … [an] inability to learn to read.”

In the ensuing decades, various hypotheses for the causes came and went. It wasn’t laziness. It wasn’t a vision problem. It wasn’t the result of an infection. Some scientists began to suspect structural differences in the brain.

Neural enigma

Searching for dyslexia clues in the brain is not simple. In part, that’s because there isn’t a single region of the brain devoted to reading. In the course of human history, reading is a relatively recent innovation. Unlike with spoken language, humans haven’t evolved a natural capacity for learning to read through exposure. Instead, learning to read requires that different areas of the brain that evolved for other purposes — including vision and sound perception — be retrained to work together to recognize and interpret written words. If scientists wanted to pinpoint the basis of dyslexia, they would need to explore the many brain regions involved in reading, as well as the neural pathways connecting them.

How does the brain learn to read? This short video explains.

Another hurdle? “It’s not really a disease,” says Albert Galaburda, the Emily Fisher Landau Professor of Neurology, Emeritus, at HMS. When Galaburda began searching for brain evidence of dyslexia back in the 1970s, advanced imaging techniques like functional magnetic resonance imaging (fMRI) were not yet available; instead, researchers studied postmortem brains. And since people didn’t typically die of dyslexia, it was rare to find a donated brain linked to a recorded case of the condition.

In 1979, Galaburda found an exception: a donated brain from a young man who had fallen through an elevator shaft to his death because his dyslexia prevented him from reading a cautionary sign. In one of the first studies exploring anatomical brain differences in people with dyslexia, published in Annals of Neurology in 1979, Galaburda and a colleague highlighted some interesting patterns that he would later also find in brains of other dyslexic people, including unusual symmetry between the two hemispheres and anomalies in the development of the cortex. Along with his mentor, Norman Geschwind, MD ’51, Galaburda’s work raised myriad associations for researchers to test, such as links between dyslexia and autoimmune disorders or levels of sex hormones.

 “Geschwind and Galaburda were among the first ones thinking about a multifactorial model — looking at all the different factors that sort of work together to cause atypical reading development,” says Nadine Gaab, an associate professor of pediatrics at HMS and a professor at the Harvard Graduate School of Education.

Clues found in the developing brain

By the time Gaab began her own research into dyslexia in 2007, new neuroimaging techniques were available for researchers to examine the brains of children living with dyslexia or those who had a familial risk for the condition — that is, a biological parent or sibling with dyslexia. At that point, “we knew a lot about how the brain of a person with dyslexia differed in activation patterns and different tasks,” Galaburda says. But an important question remained: Did dyslexia cause these differences, or did these differences cause dyslexia?

Gaab focused on answering this question. An MIT research group she was a part of focused its study on one white matter tract called the arcuate fasciculus, or the “the arc,” which connects key brain areas involved in reading: those related to vision and sound processing at the back of the brain and the inferior frontal gyrus, an area responsible for comprehension and meaning. In a subsequent longitudinal study in which the brains of kindergartners were scanned, Gaab and colleagues demonstrated that children who had lower phonological processing skills, a risk factor for dyslexia, also had smaller arcs.


Nadine Gaab sits on the bed of an MRI machine holding two kids' toys, an inflatable tiger and monkey
Nadine Gaab

After identifying that link, Gaab and colleagues set out to learn when these differences emerge. They compared brain scans from children with a familial risk for dyslexia with those from children without the familial risk and found that children at risk for the condition showed differences in the arc even before beginning formal schooling. Moreover, the rate of the structure’s development was slower among those who later developed poor reading skills regardless of familial risk. To the researchers, this suggested that some children began kindergarten with brains that were less well equipped for learning to read.

To explore how early these differences emerged, the researchers examined the brains of participants who had thus far been largely neglected in dyslexia studies: babies. Their initial study, published in Cerebral Cortex in 2017, found that infants of parents who had struggled with reading showed alterations the arc compared to infants of parents who hadn’t struggled to read. In subsequent studies, they observed a link between these alterations and phonological processing and oral language skills in kindergarten. They also found that the microstructure of the arc can be shaped by lifestyle factors, such as how early and often a child is read to.

We now know that some kids who step into kindergarten on their first day, with their little backpacks, have a heightened risk for struggling with learning to read.

While the arc is only one of several brain areas exhibiting differences in people with dyslexia, Gaab’s findings have provided an impetus for action. In addition to linking risk factors for dyslexia to specific parts of the brain, her work shows that some of these risks can be inherited. And the findings indicate that while genetics matter, environment can matter, too. Perhaps more important, they suggest that risk factors for dyslexia exist early — very early. “We now know that some kids who step into kindergarten on their first day, with their little backpacks, have a heightened risk for struggling with learning to read,” Gaab says. “That’s a really important distinction in terms of policy and how early we should find these kids and intervene.”

The value of early intervention

Despite so many children already at risk before starting school, U.S. school systems tend to identify children with dyslexia only after it’s clear that something is wrong — at around nine or ten years old. Gaab, who describes herself as a “translational neuroscientist,” has become a tireless proponent of early intervention. She advocated for a new Massachusetts law that was signed by the governor in 2018, requiring screening for dyslexia for children in kindergarten. And she’s been developing a tablet-based tool that can be used to screen children for reading problems as early as age four. This latter tool is especially useful because fMRI data, while good for exploring overall patterns of brain differences between groups, is impractical in educational contexts and does not have the sensitivity and specificity necessary to identify at-risk children.

Gaab hopes that pediatricians — who often screen for autism and ADHD — will adopt dyslexia risk screening, too. “We embrace preventive medicine; we get mammograms and checkups to identify risk factors and try to address them so that we don’t get sick,” she says. “That’s the same idea with dyslexia, to find at-risk kids early and intervene early, so that they never develop problems with reading. We call it preventive education.”

Dyslexia itself is not hazardous to anyone’s health. It really is the fact that they’re not being identified, they’re not being diagnosed, and they’re not getting the services that they need.

Proper early identification is key, adds Gaab, because studies indicate that 50 to 90 percent of at-risk readers can reach average levels of performance with targeted instruction, and that interventions are more effective in kindergarten and first grade than later on.

According to Olivardia, children who are never identified, or who live in communities without access to these interventions, might get lumped into generic remedial reading classes. But if their instruction isn’t tailored to dyslexia, “it’s as if you don’t understand the language someone is speaking, so they just speak louder,” he says. “You’re like, that doesn’t help me at all.”

Early intervention does more than help get reading levels on track. Children with dyslexia are more likely to experience depression, anxiety, and other mental health issues. But that’s not due to differences in their brains; it’s because in our society, literacy is key to academic and workplace success. “Dyslexia itself is not hazardous to anyone’s health,” says Olivardia, whose private psychotherapy practice specializes in treating children with learning disabilities. “It really is the fact that they’re not being identified, they’re not being diagnosed, and they’re not getting the services that they need.”

Education provides perspective

Olivardia understands the importance of reframing dyslexia for his patients. He talks to them about the many successful people who are thought to have had dyslexia — from Einstein to Picasso to British business magnate Richard Branson — and stresses his own observations that people with dyslexia exhibit above-average creativity and entrepreneurial skills. Research backs this up: A 2009 study in Dyslexia found a prevalence of dyslexia three times higher among entrepreneurs than people in the general population, while a higher prevalence of dyslexia has also been identified among students who pursue art or engineering. Other research points to a superior ability to connect unusual combinations of ideas among people with dyslexia.

Olivardia also draws from his experience parenting a child with dyslexia. Following his son’s diagnosis, they practiced role-playing conversations with teachers and peers about the learning disability. One day, a few weeks after diagnosis, Olivardia’s son was given lyrics to read in music class, but his dyslexia was so severe at that point that he couldn’t read the words at all.

Olivardia’s son asked a classmate to sit and sing along with him. The girl, confused, asked him why he couldn’t read. Instead of shrinking away, he calmly explained that his brain was just different — and pointed out that Tom Cruise has the same thing. “She was like, oh, OK, and that was it,” Olivardia says. “And he sat next to her. And when I picked him up, he said, ‘Dad, it was a great day.’”

“There’s a lot of hope in a label and a name,” Olivardia adds. “It gives parents, teachers, and doctors the opportunity to emphasize that these kids’ brains are wired differently — but that different does not mean they are defective.”


Molly McDonough is the associate editor of Harvard Medicine magazine.

Images: John Soares (Olivardia); courtesy of Anna Olivella and the Harvard Brain Science Initiative (Gaab)