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Spatiotemporal cortical dynamics underlying abstract and concrete word reading.

Dhond RP, Witzel T, Dale AM, Halgren E

MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA 02129, USA. polly@nmr.mgh.harvard.edu

The current study used whole-head anatomically constrained magnetoencephalography (aMEG) to spatiotemporally map brain responses while subjects made abstract/concrete judgments on visually presented words. Both word types evoked a similar posterior-to-anterior sequence of cortical recruitment involving occipital, temporal, parietal, and frontal areas from approximately 100 to 900 ms poststimulus. A prominent left temporofrontal N400m was smaller to abstract words, while the right temporal N400m was smaller to concrete words, suggesting that differences may exist in their semantic representation. The left temporofrontal decrease for abstract words is consistent with EEG studies, indicating a smaller N400 for abstract words based on a more extensive or accessible lexicosemantic network. Furthermore, the N400m peaked at approximately 420 ms and was followed by a large right hemisphere medial occipitoparietal as well as lateral parietal response to concrete words peaking at approximately 550 ms, perhaps embodying imagistic processing. These data suggest that words may be initially understood using a left-lateralized (frontotemporal) verbal-linguistic system that for concrete words is supplemented after a short delay by a right parietal and medial occipital imagistic network.

Published 20 March 2007 in Hum Brain Mapp, 28(4): 355-62.
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