For generations, scholars have debated whether language constrains the ways we think. Now, neuroscientists studying reading disorders have begun to wonder whether the actual character of the text itself may shape the brain.

Studies of schoolchildren who read in varying alphabets and characters suggest that those who are dyslexic in one language, say Chinese or English, may not be in another, such as Italian.

Dyslexia, in which the mind scrambles letters or stumbles over text, is twice as prevalent in the U.S., where it affects about 10 million children, as in Italy, where the written word more closely corresponds to its spoken sound. "Dyslexia exists only because we invented reading," said Tufts University cognitive neuroscientist Maryanne Wolf, author of Proust and the Squid: The Story and Science of the Reading Brain.

Among children raised to read and write Chinese, the demands of reading draw on parts of the brain untouched by the English alphabet, new neuroimaging studies reveal. It's the same with dyslexia, psychologist Li Hai Tan at Hong Kong Research University and his colleagues reported last month in the Proceedings of the National Academy of Sciences. The problems occur in areas not involved in reading other alphabets.

Reading brain
©Proceedings of The National Academy of Sciences
The images, made using functional magnetic resonance imaging, show brain regions with significant activation during a rhyming task. (a and b) The cortical activation associated with rhyme judgment contrasted in normal and dyslexic Chinese readers. (c) Brain regions showing group differences during rhyme judgment.

Using two brain-imaging techniques, they identified striking differences in neural anatomy and brain activity between children able to read and write Chinese easily and classmates struggling to keep pace. Both were at odds with patterns of brain activity among readers of the English alphabet.

Even when readers in both languages looked at the same written characters, the brain activity was different, other researchers found. Arabic numerals of standard arithmetic -- used by readers of Chinese and English alike -- activate different brain regions depending on which of the two languages people had first learned to read, researchers at the Chinese Academy of Sciences and China's Dalian University of Technology reported in 2006.

"In this sense, we may regard dyslexia in Chinese and English as two different brain disorders," Dr. Tan said, "because completely different brain regions are disrupted. It's very likely that a person who is dyslexic in Chinese would not be dyslexic in English."

By any measure, reading is a complex and peculiar task. At the speed of thought, readers of English turn letters they see into sounds, sounds into words, and words into meaning. Fluency is measured in milliseconds. Spelling variations are speed bumps in the brain.

Until recently, researchers who study reading abilities focused mostly on Western alphabets. English and 218 other languages, from Alsatian to Zulu, share variations of the same Latin character set. But that set is only one of 60 writing systems used among the world's remaining 6,912 spoken languages. Even so, those studies convinced many scientists and educators that the brain's response to the written word, regardless of the language, is universal.

The new research suggests they're wrong. The schooling required to read English or Chinese may fine-tune neural circuits in distinctive ways.

To learn the ABCs of English, we essentially harness our listening skills to a phonetic code. To become literate in Chinese, however, we must make much heavier use of memory, motor control and visual-perception circuits located toward the front of the brain. Children can master the 6,000 or so Chinese characters used in Mandarin and Cantonese text only by laboriously copying them out over and over again, until each abstract form becomes second nature.

"We have to recognize that the writing system in China is different, the demands on the brain are different and the characteristics of dyslexia are different," said Georgetown University pediatric learning specialist Guinevere Eden, who is incoming president of the International Dyslexia Association.

To document the effects on brain development, Dr. Eden and her colleagues are launching a five-year study in Beijing and Washington to compare the neural changes in 60 schoolchildren learning to read either Chinese or English. "Nobody has ever done this across two writing systems," Dr. Eden said.

In ways that ancient scribes never imagined, text has transformed us. Every brain shaped by reading, whether it is schooled in Chinese or English text, measurably differs -- in terms of patterns of energy use and brain structure -- from one that has never mastered the written word, comparative brain-imaging studies show. "There are real differences that emerge because of literacy," Dr. Wolf said.

Some social psychologists speculate that the brain changes caused by literacy could be involved in cultural differences in memory, attention and visual perception. In January's Psychological Science, MIT researchers reported that European-Americans and students from several East Asian cultures, for example, showed different patterns of brain activation when making snap judgments about visual patterns.

No one knows which came first: habits of thought or the writing system that gave them tangible form. A writing system could be drawn from the archaeology of the mind, perpetuating aspects of mental life conceived at the dawn of civilization.

"Once you have different writing systems in place," said University of Michigan social psychologist Richard Nisbett. "They may reinforce the perceptual and cognitive trends that preceded the invention of writing. They may go hand in glove."