The present study was designed to test differential hemispheric activation induced by emotional stimuli in the gamma band range (30±90 Hz). Subjects viewed slides with differing emotional content (from the International Affective Picture System). A signi®cant valence by hemisphere interaction emerged in the gamma band from 30±50 Hz. Other bands, including alpha and beta, did not show such an interaction. Previous hypotheses suggested that the left hemisphere is more involved in positive affective processing as compared to the right hemisphere, while the latter dominates during negative emotions. Contrary to this expectation, the 30±50 Hz band showed relatively more power for negative valence over the left temporal region as compared to the right and a laterality shift towards the right hemisphere for positive valence. In addition, emotional processing enhanced gamma band power at right frontal electrodes regardless of the particular valence as compared to processing neutral pictures. The extended distribution of speci®c activity in the gamma band may be the signature of cell assemblies with members in limbic, temporal and frontal neocortical structures that differ in spatial distribution depending on the particular type of emotional processing. q
Muller et al. REF reported increased gamma (30-50 Hz) power for a negative valence over the left temporal region.