EEG power and coherence analysis of visually presented nouns and verbs reveals left frontal processing differences

Spectral power and coherence of the electroencephalogram was measured while subjects read either a verb or a noun which initiated a short meaningful phrase. For both types of words theta-power decreased substantially relative to a prestimulus baseline at left anterior electrode sites. All other frequency bands showed less (alpha, beta) or no effects at all (gamma). The theta-power attenuation was more pronounced for verbs than for nouns, thus indicating a stronger desynchronization for verbs at left frontal sites. Coherence of the theta-band revealed that these left anterior electrodes became decoupled from left and right posterior sites, again more for verbs than for nouns. These spectral changes are assumed to reflect processing differences due to the grammatical status of the two word categories.