How the brain learns new auditory and orthographic word forms: shared and domain specific brain responses

The ability to learn new words peaks in childhood, even though adults continue to learn new words in their native language, as well in foreign languages (1). Leaning new words through reading represents a particular cognitive challenge, as the acquisition of the orthographic form is simultaneous to the learning of the phonological form. The neural mechanisms supporting the acquisition of new entries in the mental orthographic lexicon has not been extensively explored in adults, an issue that we addressed in this fMRI experiment. We assessed the learning of the phonological form and of the orthographic form of neologisms in 22 subjects. The experiment included an encoding phase when subjects read or heard and incidentally learned new-words that were repeated six times over six consecutive blocks of stimuli. Continuously changing distractors were mixed with the experimental items. In the second phase, during fMRI scanning, subjects explicitly recognized from distractors the new-words already seen/heard in the previous blocks. The event-related analysis of the fMRI data showed a common area of enhanced response in the left middle temporal gyrus for the successful recognition of non-words learned in both “listening” and “reading” conditions. There was also a double-dissociated pattern: written new-word forms recognition was associated with a specific enhancement in the left inferior frontal gyrus, the left inferior temporal/fusiform gyrus and the cerebellum, while a second region of the middle temporal gyrus was activated only for the recognition of words learned in the “listening” condition (2). This pattern of partially overlapping and dissociable systems for non-words learning in the auditory modality and in the reading modality is compatible with previous neuropsychological and anatomical observations in patient PV (3) who was completely unable to learn new-words when presented auditorily while retaining a marginal ability to learn new words when presented visually. References (1) Gathercole S.E., Baddeley A.D. Working memory and language. Hove: Lawrence Erlbaum, 1993. (2) Paulesu E., Vallar G., Berlingeri M., Signorini M., Vitali P., Burani C., et al. Supercalifragilisticexpialidocious: how the brain learns words never heard before. Neuroimage 2009; 45: 1368-77. (3) Baddeley, A.D., Papagno, C., Vallar, G. When long-term learning depends on short-term storage. Journal of memory and language 1988; 27: 586-595.