Gamma and beta frequency oscillations in response to novel auditory stimuli: A comparison of human electroencephalogram (EEG) data with in vitro models

Investigations using hippocampal slices maintained in vitro have demonstrat ed that bursts of oscillatory field potentials in the gamma frequency range (30-80 Hz) are followed by a slower oscillation in the beta 1 range (12-20 Hz). In this study, we demonstrate that a comparable gamma-to-beta transit ion is seen in the human electroencephalogram (EEC) in response to novel au ditory stimuli. Correlations between gamma and beta 1 activity revealed a h igh degree of interdependence of synchronized oscillations in these bands i n the human EEC, Evoked (stimulus-locked) gamma oscillations preceded beta 1 oscillations in response to novel stimuli, suggesting that this may be an alogous to the gamma-to-beta shift observed in vitro. Beta 1 oscillations w ere the earliest discriminatory responses to show enhancement to novel stim uli, preceding changes in the broad-band event-related potential (mismatch negativity). Later peaks of induced beta activity over the parietal cortex were always accompanied by an underlying gamma frequency oscillation as see n in vitro. A further analogy between in vitro and human recordings was tha t both gamma and beta oscillations habituated markedly after the initial no vel stimulus presentation.