CONCEPT ACTIVATION AND COORDINATION OF ACTIVATION PROCEDURE REQUIRE 2DIFFERENT NETWORKS

IN the present study, we used EEG-coherence analysis to assess general regional changes in neuronal activity related to semantic retrieval, testing the hypothesis that concept activation and coordination proced ures are neurobiologically distinguishable. Four subjects had to decid e whether or not a capital letter and a lower case letter have the ide ntical name (e.g. Aa). This task requires two mental procedures: (i) t he activation of concepts and (ii) their coordination, particularly wh en the interstimulus interval is shorter than the duration of concept activation. This memory retrieval of a concept appears to be subserved by two distinct networks: the left parietotemporal region for concept activation and the prefrontal region for coordination. (C) 1998 Rapid Science Ltd.