A new meta-analysis involving over three thousand adults and 163 brain exams sheds light on how the brain processes written language. The study explores the transformation of printed symbols into mental images, ideas, and emotions.
According to neuroscientist Sabrina Turker from the Max Planck Institute for Human Cognitive and Brain Sciences, a 2023 study revealed that, "Despite many neuroscientific investigations on language, we still know little about its organization in the human brain." She added, "Much of what we know comes from one-off studies, with small samples, and has not been confirmed by follow-up investigations."
Turker's meta-analysis, published in Neuroscience & Biobehavioral Reviews, compiled results from 163 studies using brain exams like fMRI and PET scans on 3,031 adults. The studies included various reading tasks in alphabetic languages, from recognizing isolated letters to reading complete texts aloud or silently, with real or invented words.
The research indicates that all reading tasks activate the left hemisphere, the primary center for language processing. "We found a high processing specificity for reading letters, words, sentences and texts exclusively in areas of the left hemisphere," the team noted. Reading letters and texts mainly involves the left motor and visual areas, while reading words and sentences activates multiple linguistic regions in the same hemisphere.
The meta-analysis reinforces the idea that the right cerebellum activates during all types of reading tasks, especially reading aloud. The authors write, "While the left cerebellum seems more linked to the creation of meaning [semantic function], the right contributes to the general processes of reading, probably due to its role in the production of speech."
Researchers also compared reading aloud and silent reading. Reading aloud more frequently activates auditory and motor regions. Silent reading uses brain areas responsible for coordinating various cognitive demands simultaneously.
The authors conclude that the study "deepened our understanding of the neural architecture of reading, confirmed previous results obtained by brain stimulation and may provide useful data on reading models."