Feedback modulates gamma oscillations in a hypothesis testing paradigm

We analyzed the time-varying modulation of gamma (> 30 Hz) electroencephalographic (EEG) activity exerted by positive and negative feedback in a hypothesis testing paradigm. 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 was convolved with a family of complex wavelets and brain potentials were extracted in the gamma range. Feedback-related modulations were found as early as 100 ms after feedback onset, as well as in the 300–600 ms time-window. The results were discussed in terms of functional and neurophysiological models of feedback.