Figure 3.

Evidence showing the effect of placebo treatment from the partitions of EEG data during pain perception rating and after rating. (A) A trend toward significant interaction effect was identified from frequency analyses including EEG data during the rating period (left panel); the mean values of the amplitudes of alpha oscillation (measured at FCz) from each condition are shown (F: F value of the interaction effect between the factors “pain” and “placebo”; corr.: corrected for multiple comparisons; middle panel); a significant correlation was observed between decrease in pain intensity during noxious stimulation after placebo treatment (II–IV) and the increase in the amplitude of alpha oscillation measured at FCz (IV–II; right panel). (B) No significant interaction effect was identified from frequency analyses that included EEG data of the time periods after rating (left panel); the corresponding results of mean amplitude values are shown (middle panel); marginally significant correlation was observed (right panel).