Spatio-Temporal Analysis of Electric Brain Activity during Semantic and Phonological Word Processing

Abstract:
In order to investigate differences in map topographies and brain activation during semantic and phonologic processing, EEG was recorded in 14 subjects from 41 equally-spaced electrodes during two language experiments. In the first, the subjects had to judge whether two successively presented words were semantically related or not. In the other, they had to judge whether word pairs rhymed or not. The ERPs after second words (600 ms) were compared between the two experiments and divided into temporally successive segments of stable map configurations. This revealed, in each condition ten segments of which only the 6th and the 7th occurring between 280-380 ms differed between the semantic and the phonologic processing. In both tasks, the duration of the 6th segment correlated with the RT. The estimated generators in the brain for each segment, using a 3-D localizing method, revealed in both tasks a network of active areas that involved mainly left postero-temporal and left antero-temporal regions. These results show that tracing electric activity allows to unfold neuronal networks involved in language processing and to determine the modules of the network which are involved in the task demand.