Positive and negative performance feedbacks have been shown to differentially modulate amplitudes of the associated electroencephalographic (EEG) brain activity. In the present study, we tested whether feedback also modulates the organization of neuronal oscillations. Ten college students serially tested hypotheses concerning a hidden rule by judging its presence or absence in triplets of digits and revised them on the basis of an exogenous performance feedback. The EEG signal time-locked to feedback was convolved with a family of complex wavelets. The time-varying spectral entropy of the resulting time-frequency representation was then computed. The results showed that feedback differentially modulated spectral organization at frontal and posterior scalp regions around 200 ms and in the 300-500 ms range. Spatio-temporal principal component analysis (PCA) indicated that feedback-specific modulations essentially resulted from the interplay between fronto-polar, fronto-central, and parieto-occipital components. Functional and methodological implications were discussed. (c) 2007 Elsevier B.V. All rights reserved.