Children who later develop dyslexia already show subtle differences in how a visual-language brain region responds to repeated written words in kindergarten, before formal reading lessons begin, according to a longitudinal study published in Developmental Cognitive Neuroscience. At the same time, they process repeated faces, houses, and objects much like their peers, suggesting that early brain differences in dyslexia are tied to print rather than reflecting a general difficulty adapting to repeated sights.
Dyslexia is a learning condition marked by persistent difficulty reading accurately and fluently despite typical intelligence and adequate instruction. One proposed explanation involves neural adaptation, in which brain cells respond less intensely when a person sees or hears the same item repeatedly compared to encountering different items. That drop in activity reflects how efficiently a brain region recognizes familiar patterns and tunes itself to specific categories.
Support for that idea came from a 2016 neuroimaging study of adults and school-age children, which found weaker neural adaptation in adults with dyslexia across repeated spoken words, written words, faces, and objects, and in children with dyslexia for spoken words. Those authors proposed that a broad failure to adapt rapidly to repeated input might be a core cause of dyslexia rather than a consequence, though later studies in adults and older children yielded mixed results.
All of those earlier studies shared a major catch: every participant already knew how to read. Because people with dyslexia often find reading frustrating and read far less than fluent peers do, scanning literate individuals could not settle whether weaker brain adaptation precedes reading trouble or stems from less practice.
Much of the visual work of reading happens in the left ventral occipito-temporal cortex, a strip of tissue along the underside of the left hemisphere where the visual occipital lobe meets the language-linked temporal lobe. Evidence from a 2018 multimodal brain-imaging study indicates that its back section extracts visual shapes while its front section connects written words to the language network. This region’s groundwork forms early, as an earlier longitudinal neuroimaging study of five-year-old pre-readers found that brain connections at age five predicted where word specialization emerged at age eight.
Young children also learn letters informally at home, giving the brain an early chance to tune itself to print. In a 2023 study co-authored by three of the same researchers using the same Polish cohort, six-year-old kindergarteners’ brains already engaged language areas for printed words prior to schooling, unlike for faces, houses, or unfamiliar symbols. Extending that project to third grade, Anna Banaszkiewicz, Katarzyna Jednoróg, and colleagues at the Nencki Institute of Experimental Biology of the Polish Academy of Sciences tested whether weaker adaptation predates reading instruction in dyslexia and extends beyond words.
The team preregistered its primary hypotheses and analysis plan on the Open Science Framework, later modifying the plan in response to peer reviewers, and posted data and code publicly. Targeted region-of-interest group comparisons were conducted as non-preregistered exploratory analyses. Right-handed, monolingual Polish pre-readers without neurological conditions or reported ADHD symptoms were scanned in kindergarten, before formal reading lessons begin in Poland, and again in third grade (two pandemic-era intermediate visits had low attendance and were omitted).
In third grade, child psychologists diagnosed dyslexia in children with reading difficulties, with two unassessed poor readers included based on severely low first- and second-grade reading scores. Some participants had also begun reading a few words on their own before the kindergarten scan. To keep those early differences from skewing the baseline comparison, the researchers matched 16 children with dyslexia (average age 6.6 in kindergarten and 9.7 in third grade) with 16 typical readers (average age 6.8 and 9.9) on kindergarten age and word reading. They also checked longitudinal results across all 47 children with usable scans at both ages and analyzed early skill links across 59 kindergarteners.
In kindergarten, children completed tests of non-verbal IQ, visual attention, letter knowledge, and rapid naming speed (how fast they named rows of colors and objects aloud). They also completed tasks measuring phonological awareness, the ability to recognize and manipulate spoken sounds in words, such as spotting rhymes, matching starting sounds, and breaking words into speech sounds. At both ages, reading fluency was measured by how many real Polish words and pronounceable made-up words (testing sounding-out skill) children read aloud in a minute.
Brain activity was recorded using functional magnetic resonance imaging (fMRI), a non-invasive scan tracking blood-flow changes linked to neural activity, over 20.5 minutes. Children viewed six-image sequences from five categories: short Polish nouns, unfamiliar invented symbols matched to the visual complexity of words (false fonts), neutral children’s faces, houses, and everyday objects. Sequences either showed six different items from a category or repeated one item six times, while children pressed a button whenever a red dot appeared.
Neural adaptation was calculated by subtracting brain activity during repeated sequences from activity during mixed sequences. Alongside whole-brain tests, exploratory analyses targeted category-selective visual hubs in both hemispheres, examining the ventral occipito-temporal cortex for words and the fusiform face area on the underside of the temporal lobe for faces. They also examined the lateral occipital cortex near the back of the brain for objects. To account for individual variation, the team used both group-defined maps and individualized maps of each child’s 100 most category-responsive voxels (tiny three-dimensional scan units), splitting the word-responsive region into front and back sections.
In kindergarten, the 16 children later identified with dyslexia and 16 matched controls did not differ significantly in IQ, phonological awareness, rapid naming, letter knowledge, visual attention, or early reading, averaging 3.7 versus 6.1 real words per minute and 3.1 versus 5.0 made-up words per minute. By third grade, both groups had progressed, but typical readers read more than twice as many real words per minute as children with dyslexia (85.6 versus 39.2) and far more made-up words (47.5 versus 28.3).
Across the whole-brain analyses, group differences, changes over time, and group-by-age interactions were not statistically significant for words or any non-linguistic category. Within individual groups at third grade, typical readers showed whole-brain word adaptation in the left ventral occipito-temporal cortex only under a looser statistical correction than the study’s standard threshold. Dyslexic children showed third-grade word adaptation further back in visual cortex. Both groups adapted to objects, faces, and houses at one or both ages, whereas neither adapted reliably to unfamiliar false-font strings in the longitudinal analysis, though a weak effect appeared in the larger kindergarten sample.
Within the left ventral occipito-temporal cortex, however, children who developed dyslexia showed weaker neural adaptation to written words than typical readers (an effect also seen in the full 47-child longitudinal sample). That gap was already present in kindergarten and stayed steady through third grade, as neither overall change over time nor the group-by-age interaction was statistically significant. Individualized maps localized this difference to the region’s left front section, whereas differences in the left back section and on the right side were not statistically significant.
Object adaptation in the lateral occipital cortex did not differ significantly between groups. Group-defined maps of the right fusiform face area showed rising face adaptation over time only in controls in both the matched and full longitudinal samples, but that pattern did not appear in individualized maps.
This largely intact face and object adaptation stands in tension with an electroencephalography study of adults with dyslexia, which found reduced electrical brain responses when distinguishing individual faces and objects despite typical accuracy and speed. That earlier study, however, recorded split-second scalp electrical waves during active matching tasks in adults rather than fMRI blood-flow adaptation to passively viewed images in children.
Across all 59 kindergarteners, after adjusting for age and IQ, stronger word adaptation in the group-defined left ventral occipito-temporal cortex showed modest positive associations with phonological awareness and early word and made-up word reading (and with word reading in the individualized front left section). None of these relationships remained statistically significant after adjusting for multiple comparisons, however.
Because weaker word adaptation in the left front section preceded formal schooling in skill-matched kindergarteners, the authors suggest it is unlikely to stem solely from reading less during elementary school, proposing instead that subtle early tuning differences for print contribute to reading difficulties along a spectrum. They also propose that false-font adaptation was weak and inconsistent because higher-level visual adaptation requires familiarity and language links that kindergarteners had begun forming for real letters but lacked for invented symbols.
There are a few things to keep in mind when interpreting these findings. The matched longitudinal comparison included just 16 children per group, and the region-of-interest tests that detected the word-adaptation gap were exploratory rather than preregistered. Meanwhile, the preregistered whole-brain comparisons and the multiple-test-adjusted skill correlations were not statistically significant, indicating that the difference is subtle and unsuitable for identifying dyslexia risk in individual children.
Even though Polish kindergartens omit formal reading lessons, the children already recognized dozens of uppercase and lowercase letters on average (about 36 in the dyslexic group and 45 in controls) and read a few words per minute. Reduced word adaptation in kindergarten precedes classroom instruction rather than all home exposure to print, and an observational study cannot establish on its own that weaker adaptation causes later reading struggles.
Pandemic-related absences in first and second grade also left a three-year gap between scans, potentially missing a temporary surge in print sensitivity during early reading instruction, and the visual-only task leaves open whether auditory adaptation differences also appear before school. Future studies tracking larger cohorts at closer intervals are needed to test how consistent this front-region difference is and whether early brain scans predict reading outcomes beyond behavioral pre-reading checks.
The study, “Early Differences in Neural Adaptation to Written Words Before Reading Instruction in Dyslexia,” was authored by Anna Banaszkiewicz, Katarzyna Chyl-Tanaś, Hanna Górecka, Karolina Zielińska, Anna Redeł, Anna Szukało, Agnieszka Dębska, and Katarzyna Jednoróg.