Developmental aspects of automatic word processing: language lateralization of early ERP components in children, young adults and middle-aged subjects.

Reading words elicits a very early evoked potential termed "recognition potential" with a latency of about 150 ms and clearly located in left posterior regions. A review of the current literature indicates that N150 marks the automatic lexical classification of a word, is relatively independent of the task, and is followed by a later negative and more anterior component which is sensitive to the task. However, from the literature it is not clear whether the left lateralization of the neural networks involved in word recognition changes with age and experience, and how this lateralization is related with behavioral performance. To this aim, based on a previously validated paradigm [Spironelli, C., Angrilli, A., 2006. Language lateralization in Phonological, Semantic and Orthographic tasks: a slow evoked potential study. Behavioral Brain Research 175, 296-304; Spironelli, C., Angrilli, A., 2007. Influence of Phonological, Semantic and Orthographic tasks on the early linguistic components N150 and N350. International Journal of Psychophysiology 64, 190-198], we ran an experiment on three samples of subjects, 28 children (mean: 10 years), 22 young adults (23 years) and 20 middle-aged subjects (59 years). Subjects had to read the same sample of words in three blocked tasks, Orthographic, Phonological and Semantic, while EEG was recorded from 38 scalp locations. Analysis performed on N150 and four regions of interest/quadrants revealed typical significant left posterior negativity in young and aged subjects, but reversed lateralization and greater right negativity in children compared with the two adult groups. Analysis of the later N350 revealed a significant three-way group x laterality x task interaction, showing greater left negativity on the Phonological task only in the two adult groups, and a bilateral component in children. Results indicate that the functional lateralization of linguistic neural networks involved in automatic word recognition and in phonological processing is not yet developed in linguistically competent children aged 10 years, whereas the observed lateralization is relatively stable and not degraded in moderately aged subjects. Results are discussed in view of their implications for age-related linguistic pathologies.