FRONTAL GAMMA-BAND ENHANCEMENT DURING MULTISTABLE VISUAL-PERCEPTION

The aim of our study was to find out whether an increase in the gamma band may be related to the reversal phase during viewing of an ambiguo us pattern. The present study describes the significant gamma band (30 -50 Hz) activity increase in EEG during states of perceptual switching (reversal state). In our experiments the multistability was induced w ith an ambiguous stimulus pattern, known as stroboscopic alternative m otion (SAM). The investigations carried out in ii subjects included a measuring strategy with three different experimental conditions: (1) r ecording of spontaneous EEG as baseline; (2) recording of the EEG duri ng naive observation of the ambiguous pattern; (3) recording of EEG du ring active observation of SAM. The results indicate that the multista ble perception is one of the multifold cognitive processes giving rise to 40 Hz enhancement in the entire cortex. The most significant 40 Hz enhancements were measured in frontal areas and can reach increases o f 40 to 50% in states of naive and active observations of SAM, respect ively, in comparison to spontaneous EEG recordings. The results indica te that the increase of frontal gamma band is related to the destabili zation of the perceptual system when viewing multistable patterns.