Scalp electrical potentials reflect regional cerebral blood flow responses during processing of written words

Functional brain imaging studies with positron emission tomography (PET) have identified blood flow changes in widely separated areas of the brain during the performance of word-related tasks. In the present study, we have utilized event-related electrical potentials (ERPs) to investigate the temporal relationships among cortical areas previously identified by PET to be differentially activated when performing a task involving generating the uses of visually presented nouns versus reading aloud. ERPs showed strong task-related differences over left and middle inferior frontal and left parietotemporal regions. Frontal and left parietotemporal channels revealed these differences around 200 and 700 msec, respectively, after word presentation. These results provide the time course for parts of the anatomical circuit involved in generating the meaning of a word. Our results also demonstrate how combining the spatial localization of PET with the temporal resolution of ERPs greatly enhances the capacity to understand the mechanisms involved in human cognition.