Language processing modulated by literacy: A network analysis of verbal repetition in literate and illiterate subjects

Previous behavioral and functional neuroimaging data indicate that certain aspects of phonological processing may not be acquired spontaneously, but a re modulated by learning an alphabetic written language, that is, learning to read and write. It appears that learning an alphabetic written language modifies the auditory-verbal (spoken) language processing competence in a n ontrivial way. We have previously suggested, based on behavioral and functi onal neuroimaging data, that auditory-verbal and written language interact not only during certain language tasks, but that learning and developing al phabetic written language capacities significantly modulates the spoken lan guage system. Specifically, the acquisition of alphabetic orthographic know ledge has a modulatory influence on sublexical phonological processing and the awareness of sublexical phonological structure. We have suggested that developing an orthographic representation system for an alphabetic written language, and integrating a phoneme-grapheme correspondence with an existin g infrastructure for auditory-verbal language processing, will result in a modified language network. Specifically, are suggest that the parallel inte ractive processing characteristics of the underlying language-processing br ain network differ in literate and illiterate subjects. Therefore, the patt ern of interactions between the regions of a suitably defined large-scale f unctional-anatomical network for language processing will differ between li terate and illiterate subjects during certain language tasks. In order to i nvestigate this hypothesis further, we analyzed the observed covariance str ucture in a PET data set from a simple auditory-verbal repetition paradigm in literate and illiterate subjects, with a network approach based on struc tural equation modeling (SEM). Based on a simple network model for language processing, the results of the present network analysis indicate that the network interactions during word and pseudoword repetition in the illiterat e group differ, while there were no significant differences in the literate group. The differences between the two tasks in the illiterate group may r eflect differences in attentional modulation of the language network, execu tive aspects of verbal working memory and the articulatory organization of verbal output. There were no significant differences between the literate a nd illiterate group during word repetition. In contrast, the network intera ctions differed between the literate and illiterate group during pseudoword repetition. In addition to differences similar to those observed in the il literate group between word and pseudoword repetition, there were differenc es related to the interactions of the phonological loop between the groups. In particular, these differences related to the interaction between Broca' s area and the inferior parietal cortex as well as the posterior-midinsula bridge between Wernicke's and Broca's area. In conclusion, the results of t his network analysis are consistent with our previously presented results a nd support the hypothesis that learning to read and write during childhood influences the functional architecture of the adult human brain. In particu lar, the basic auditory-verbal language network in the human brain is modif ied as a consequence of acquiring orthographic language skills.