Processing of positive versus negative emotional words is incorporated in anterior versus posterior brain areas : an ERP microstate LORETA study

The spatio-temporal organization of the neural activity that underlies perception of emotional valence was studied analyzing 33-channel event-related potential maps (ERP maps) from 21 normals while reading a sequence of emotional positive, negative and neutral words; subjects were asked to repeat the last word if a question mark followed; they were not informed that the study concerned emotions. Brain electric activity to emotional positive and negative words was compared. Microstate segmentation of the 113 ERP maps (corresponding to the 448 ms of word presentation) identified 14 microstates, i.e. putative steps of information processing. Three microstates, #4 (90-122 ms), #7 (178-202 ms) and #9 (242-274 ms) showed global map topography differences between emotional positive and negative words. During these three microstates, the involved brain areas were identified using Low Resolution Electromagnetic Tomography (LORETA). The results showed that the extraction of valence during the three emotion-sensitive microstates was incorporated in different brain areas: positive as well as negative emotional words caused predominant left-hemispheric activation in #4 and #9, but predominant right-hemispheric activation in #7. The striking communality across the three microstates however was that in each of them, positive words compared to negative words clearly evoked significantly more anterior brain activity.