EVENT-RELATED BRAIN POTENTIAL IMAGING OF SEMANTIC ENCODING DURING PROCESSING SINGLE WORDS

Functional brain imaging studies with positron emission tomography (PE T) have identified blood flow changes in widely separated areas of bra in during the performance of word processing tasks. In the present stu dy we have utilized event-related brain potentials (ERPs) to investiga te the temporal relationships among cortical areas previously identifi ed by PET to be differentially activated when performing semantic task s with visual words. ERPs revealed task-related differences over the c entral and left inferior frontal regions around 170 and 220 ms, respec tively, over a left occipital region around 200 ms, over a large left parietotemporal region around 600 ms, and finally over the right tempo ral lobe around 800 ms after the word presentation. Analysis of topogr aphic maps add dipole sources as well as PET data allowed relating fro ntal midline positivity around 170 ms to the anterior cingulate activa tion, and left inferior frontal positivity around 220 ms to the PET ac tivation of the left inferior prefrontal cortex. The left parieto-temp oral positivity around 600 ms seems to reflect the activity: of Wernic ke's area, The right anterior temporal negativity beginning around 800 ms and peaking around 1100 ms may reflect the activity of the right i nsula. The left occipital negativity around 200 ms is likely to reflec t activation of a visual word-form area in the left occipital lobe. Th ese results provide the time course for parts of the circuitry involve d in semantic processing of words and also demonstrate how combining t he spatial localization of PET with the temporal resolution of ERPs he lps to understand the brain mechanisms involved in human cognition. (C ) 1998 Academic Press.