New neuroscience research upends traditional cognitive models of reading

February 17, 2025

How does your brain transform written words into spoken ones in mere milliseconds? A new study published in The Journal of Neuroscience has found that a key brain region traditionally associated with speech production is engaged in reading far earlier than expected. Using targeted brain stimulation, researchers demonstrated that the left posterior inferior frontal cortex (pIFC) is essential for translating written words into spoken language within just 100 milliseconds after seeing a word—well before traditional models suggest.

For decades, scientists have sought to understand how the brain reads, particularly the sequence of events that turn written text into spoken words. Traditional models propose a “serial cascade,” where written words are processed in stages: visual recognition in the fusiform gyrus, phonological conversion in the supramarginal gyrus, and speech production in the pIFC. This sequence implies that each stage waits for input from the previous one.

However, recent neuroimaging studies show simultaneous activation of these regions during reading, raising questions about whether they operate independently or interact directly. The researchers aimed to clarify the role of the pIFC in reading by using transcranial magnetic stimulation (TMS), a non-invasive technique that temporarily disrupts brain activity.

“Traditional cognitive models of reading assume that speech production occurs after initial visual and phonological processing of written words,” explained study author Kimihiro Nakamura, the principal investigator at the Systems Neuroscience Section at the National Rehabilitation Center Research Institute.

“This seems a plausible and reasonable a priori assumption, but a series of more recent magnetoencephalography (MEG) studies show that the pIFC, classically associated with spoken production, responds to print at 100-150 ms after word-onset, almost simultaneously with posterior brain regions for visual and phonological processing. Moreover, the functional significance of this fast neural response is also unclear, because the left pIFC is now known to mediate different aspects of linguistic/non-linguistic processing. We therefore wanted to fill this gap between cognitive models and empirical data from functional brain imaging.”

In the study, 50 adults participated in two experiments. In the first experiment, participants performed three tasks: reading words aloud, making semantic judgments (deciding if a word referred to an animal or plant), and distinguishing the text’s color (a perceptual control task). The second experiment introduced an object-naming task to compare processes involved in reading to those used for general spoken language production.

The fusiform gyrus also showed early involvement. Disrupting its function at 100 milliseconds impaired both reading and semantic tasks, highlighting its role in visual word recognition. Unlike the pIFC, however, the fusiform gyrus did not show a task-specific effect; its disruption affected tasks requiring both phonological and semantic processing.

“Most of the current knowledge of spatiotemporal dynamics in reading is derived from functional neuroimaging data with high-temporal resolution, such as ERP and MEG, according to which posterior brain systems responsible for visual and phonological processing respond to print at 250-500 ms after stimulus-onset,” Nakamura told PsyPost. “While the main goal of the study was to dissect the causal role of early pIFC activation in reading, our TMS results revealed that those other systems for reading also act much faster than assumed by most neurocognitive models of reading derived from ERP/MEG data. Because TMS is a brain stimulation method for transiently disrupting local neural activity, we argue that the observed gap could be attributed to possibles difference in timing between actual neuronal firing and peak response latencies estimated from ERP/MEG waveforms.”

The supramarginal gyrus displayed delayed activation, with TMS disrupting performance only at 150 milliseconds or later. This finding aligns with its established role in phonological processing, which occurs after initial visual recognition of words.

While such direct and rudimentary neurocognitive pathway for print-to-sound conversion is known to help decipher text in children and people with brain damage, little is known about its role and status in proficient adult readers, who primarily rely on more effective whole-word recognition systems. In sum, we therefore suggest that the brain may have more resources than cognitive models believe – the seemingly dormant, fast sublexical pathway for pronunciation is fully functioning in literate adults.”

These findings not only deepen our understanding of how the brain handles reading but also have potential applications in addressing reading-related challenges, such as dyslexia. By identifying the early and critical role of the pIFC, researchers have opened new avenues for exploring how these pathways develop in literacy and how they might be enhanced through targeted interventions.

“We believe that the precise temporal dynamics during reading is of critical importance for understanding the neurophysiology of dyslexia and related disorders,” Nakamura said. “In this context, by combining such temporal dynamics information and high temporal resolution methods (e.g., EEG and electrical cortical stimulation), we are particularly interested in developing novel neuromodulation methodology for effective remediation and training dedicated to these disorders.”

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