Learning to read written text fundamentally alters the pathways the human brain uses to process spoken words. According to a recent study, adults with formal literacy training recruit a specialized region on the right side of the brain to identify isolated speech sounds, a neurological response absent in people with limited reading education. The research was recently published in the journal Cortex.
Spoken language has been a universal behavior of human beings for hundreds of thousands of years. Reading and writing are relatively recent cultural inventions. Because the brain did not evolve specifically to read, it must repurpose existing visual and linguistic networks to make sense of written text.
Neuroimaging research demonstrates that mastering the written word triggers physical and functional changes in the left hemisphere of the brain. This occurs particularly in areas responsible for connecting visual shapes to specific sounds. It remains an open question whether learning to read also changes the fundamental ways people hear and process everyday spoken language.
Reading education explicitly teaches a cognitive skill called phonological awareness. This is the ability to recognize and manipulate the individual auditory components of a word. A common test of this skill involves asking a student to identify a specific syllable, recognize a rhyme, or repeat a completely made-up word with no actual meaning.
People who know how to read perform much better on tests of phonological awareness than people who cannot read. Repeating a fake word relies entirely on short-term memory for pure sounds, completely divorced from short-term memory for semantic meaning. Literate individuals can hold these sound sequences in their minds easily, while illiterate adults generally struggle to recall arbitrary sound strings.
To find out if this learned skill influences brain activity during natural listening, a team of researchers designed a specialized audio test. Mariana P. Nucci, a cognitive neuroscientist at the University of São Paulo, led the research team. Nucci and her colleagues wanted to observe how brains with drastically different educational backgrounds handle a challenging listening task.
Finding a large group of adults without formal education who also live near a modern brain scanner presents a practical challenge. The researchers recruited participants from the city of São Paulo, Brazil. The region has a thriving scientific community but also experiences high rates of historical wealth inequality, meaning many older adults grew up without access to consistent schooling.
The researchers recruited three distinct groups of healthy volunteers. The sample included 23 highly educated young adults, 21 highly educated older adults, and 15 older adults with very low levels of formal education. The volunteers in the last group are classified as functionally illiterate. They might recognize basic letters or common names, but they cannot generally read a long text for comprehension.
Participants entered a functional magnetic resonance imaging scanner, a machine that tracks blood flow in the brain to measure neural activity. The volunteers listened to an extended audio narrative through headphones. They held a small device in their left hand and were instructed to press a button every time they heard a specific target word.
The volunteers performed this word-monitoring task in two different languages. First, they listened to a story in their native language, Portuguese. Because they could understand the narrative, they could use the semantic context of the story to anticipate the target word’s arrival.
Next, they listened to a structurally identical story in Japanese, a language none of the participants understood. In this condition, listeners could not rely on narrative context or meaning. They had to consciously monitor the continuous stream of foreign speech to detect a specific sequence of unfamiliar sounds. The researchers also included a baseline task that required participants to press a button when they heard a simple tone in a silent background.
The volunteers with low levels of formal education performed relatively well when listening in Portuguese. They successfully pushed the button for the native target word roughly 90 percent of the time. When the language switched to Japanese, their performance dropped dramatically.
The functionally illiterate adults caught the target word only 17 percent of the time in the unknown language. By comparison, the highly educated older adults scored a 48 percent success rate. The highly educated young adults caught the target word 75 percent of the time. Both groups of literate adults performed notably better than the group without reading education.
Brain imaging data provided a physiological explanation for these behavioral differences. When listening to their native language, all three groups displayed similar patterns of brain activation. The noticeable differences in brain activity emerged strictly during the Japanese listening task.
The highly educated older adults showed a distinct spike in activity in the right inferior frontal gyrus. This region sits near the temple on the right side of the head. It is the direct counterpart to Broca’s area, a highly studied region on the left side of the brain that governs speech production and language comprehension.
The older adults who lacked formal education completely failed to recruit this right-sided region during the unknown language task. The researchers noted that success in finding the hidden Japanese words correlated heavily with an individual’s score on standard reading proficiency tests. This indicates that the right inferior frontal gyrus is involved in applying explicit phonological analysis to spoken sounds. This specific cognitive ability seems to develop primarily through years of classroom education and literacy training.
The brain scans also revealed expected differences related to the general aging process. The highly educated older adults displayed more widespread brain activity than the highly educated young adults across both language tasks. Older brains often recruit extra neurological pathways to perform basic tasks. Scientists theorize this overactivation helps compensate for age-related changes in general physiological efficiency.
The study includes a few acknowledged limitations. The group of functionally illiterate adults was relatively small. This is largely due to the strict exclusion criteria and the inherent difficulty of finding eligible volunteers who could safely participate in a noisy brain imaging environment. Small sizes in research samples can sometimes restrict the statistical power of neuroimaging findings.
The authors also emphasize that educational background is deeply tied to broader life experiences. The functionally illiterate participants generally faced more socioeconomic adversity and fewer occupational opportunities than the highly educated cohort throughout their lives. Poverty, stress, and poor access to healthcare can also influence cognitive development and resting brain organization independently of reading ability.
Future studies could test adults with low literacy using nonverbal audio tasks to see if their lack of brain activation in the right frontal lobe is specific to language. Researchers might also look at tasks requiring intense visual focus to determine if socioeconomic disadvantages generally alter how the brain allocates sustained attention. Expanding this research would help clinicians better understand how to structure cognitive therapies and rehabilitation programs for older patients with diverse educational backgrounds.
The study, “Literacy modulates engagement of the right inferior frontal gyrus in phonological processing of spoken language,” was authored by Mariana P. Nucci, Kelly Cotosck, Katerina Lukasova, Ricardo Nitrini, Cheryl L. Grady, Edson Amaro Jr., and Jed A. Meltzer.
