Now you'll feel it - now you won't: EEG rhythms predict the effectiveness of perceptual masking
Do ongoing brain states determine conscious perception of an upcoming stimulus? Using the high temporal resolution of EEG, we investigated the relationship between pre-stimulus neuronal oscillations and the perceptibility of two competing somatosensory stimuli embedded in a backward masking paradigm. We identified two pre-stimulus EEG signatures predictive for a supra-threshold yet weak target stimulus to become perceptually resistant against masking by a stronger distractor stimulus: (i) 500 ms prior to a target which will withstand masking the left frontal cortex becomes active, as indexed by desynchronization of the regional beta rhythm at ~ 20 Hz, and (ii) an additional attenuation of both mu (~ 10 Hz) and beta 'idling' rhythms is following at those pericentral sensorimotor cortices which are going to process the upcoming target stimulus. Furthermore, the probability for target perception strongly correlates with the individual level of pre-target amplitudes in these bands and locations. We suggest that the early activation of left frontal areas involved in top-down attentional control is critical for preventing backward masking and leads the preparation of primary sensory cortices: The ensuing pre-stimulus suppression of sensory idling rhythms warrants an intensified post-stimulus processing and thus effectively promotes conscious perception of supra-threshold target stimuli embedded into an ecologically relevant condition featuring competing environmental stimuli.