Dependence of EEG spectral power density on the meaning of stimuli

Spectrum analysis of event-related brain activity periods was done in the 2-32 Hz frequency band. Three tests were performed in which the flash acted as an attention requiring stimulus or as a negative or a positive reinforcement. EEG was recorded from 8 scalp leads on 24 human subjects. During the performance-adapted time conditioning task, with the flash acting as a negative reinforcer, there was a marked increase of densities for frequencies 2-7 Hz and a decrease for 8-13 Hz in the fronto-centro-parietal leads. Power shifts are discussed in relation to the different meaning of the flashes.