An anatomical signature for literacy

It has long been known that people who have not learned to read (illiterates) do very poorly on tasks that involve doing things with abstract sound-based properties of words (or nonwords) - see Morais (1993) for a brief review. For instance, illiterate adults have been found to be almost unable to perform a task that involves "deleting" or "adding" a phone at the beginning of a nonword whereas literate adults (from the same sociocultural environment) could easily perform the task (Morais et al., 1979).

Castro-Caldas, Petersson,Reis, Stone-Elander and Ingvar (1998) followed this up in a PET study that looked at the energy response of cortical neurons to oral language processing tasks in illiterate and literate adults. The two groups performed similarly and activated similar areas of the brain when repeating real words. However the illiterate group had more difficulty repeating nonwords correctly and when doing this task different brain regions were activated compared to the literate group.

In this recent study examining the issue of how literacy changes cortical structure and functioning Manuel Carreiras and colleagues used MRI to examine cortical connectivity and neural activation in 42 adult Colombian ex-guerrilla fighters, 20 who had completed a literacy programme and 22 who had yet to start the course. What did they find?

Abstract
Language is a uniquely human ability that evolved at some point in the roughly 6,000,000 years since human and chimpanzee lines diverged1,2. Even in the most linguistically impoverished environments, children naturally develop sophisticated language systems3. In contrast, reading is a learnt skill that does not develop without intensive tuition and practice. Learning to read is likely to involve ontogenic structural brain changes4–6, but these are nearly impossible to isolate in children owing to concurrent biological, environmental and social maturational changes. In Colombia, guerrillas are re-integrating into mainstream society and learning to read for the first time as adults. This presents a unique opportunity to investigate how literacy changes the brain, without the maturational complications present in children. Here we compare structural brain scans from those who learnt to read as adults (late literates) with those from a carefully matched set of illiterates. Late-literates had more white matter in the splenium of the corpus callosum and more grey matter in bilateral angular, dorsal occipital, middle temporal, left supramarginal and superior temporal gyri. The importance of these brain regions for skilled reading was investigated in early literates, who learnt to read as children. We found anatomical connections linking the left and right angular and dorsal occipital gyri through the area of the corpus callosum where white matter was higher in late-literates than in illiterates; that reading, relative to object naming, increased the interhemispheric functional connectivity between the left and right angular gyri; and that activation in the left angular gyrus exerts top-down modulation on information flow from the left dorsal occipital gyrus to the left supramarginal gyrus. These findings demonstrate how the regions identified in late-literates interact.


References

Carreiras et al (2009). An anatomical signature for literacy, Nature, 461,983-986.

Castro-Caldas, A. Petersson, K. M. Reis, A. Stone-Elander, S. & Ingvar, M (1998). The illiterate brain Learning to read and write during childhood influences the
functional organization of the adult brain, Brain, 121, 1053–1063

Morais J. Phonemic awareness, language and literacy. In: Joshi RM,
Leong CK, editors. Reading disabilities: diagnosis and component
processes. Dordrecht: Kluwer Academic; 1993. p. 175–84.

Morais J, Cary L, Alegria J, Bertelson P. (1979). Does awareness of speech
as a sequence of phones arise spontaneously? Cognition, 7, 323–31.