This revealed a hublike structure in which the right posterior parietal cortex synchronized most prominently with other nodes of the
network. Thus, in contrast to the widespread stimulus-related decrease in local AG 14699 beta-band activity (compare Figure 2B), long-range beta-synchrony was enhanced in a highly structured network during stimulus presentation. If beta-band synchronization within this network was functionally relevant for processing of the sensory stimulus, intrinsic fluctuations of synchrony may predict the subjects’ alternating perception of the constant physical stimulus. Indeed, we found that beta-synchrony was not only enhanced during stimulus processing but also predicted the subjects’ percept of the stimulus. We compared coherence within the identified network for trials in which the subjects perceived the stimulus as “bouncing” or “passing.” This yielded a highly significant difference (Figure 3D, permutation-test, p < 0.0001) with enhanced beta-coherence for bounce trials. Receiver operating characteristic (ROC) analysis revealed that, even on a single-trial
level, the strength of beta-coherence significantly predicted the subjects’ percept (permutation-test, p < 0.0001). In other words, when large-scale beta-band synchronization was enhanced between frontal, parietal, and extrastriate areas, subjects were more likely to perceive the same sensory stimulus as bouncing rather than passing. Although this percept-predictive difference in synchronization overall had a network structure similar to the stimulus-related increase in synchrony,
we found the strongest perception-related effects Estrogen antagonist for synchronization with frontal regions (Figure 3E). In principle, differences in neural activity between bounce and pass trials may either reflect neural processes directly causing the subjects’ percepts or, alternatively, may reflect only secondary processes ensuing from the alternating percept. The time course of neural activity relative to the perceptual ambiguity provides critical evidence to resolve this question. We GPX6 thus exploited the temporal resolution of EEG and tested whether the difference in coherence temporally preceded the time when the stimulus became ambiguous (t = 0 s). Indeed, we found that already before the time of bar overlap (time < −0.125 s; accounting for the size of the analysis window) coherence significantly predicted the subjects’ percepts (ROC analysis, permutation-test, p = 0.0002). This provides strong evidence that, rather than merely being a consequence of the different percepts, fluctuations of large-scale beta-synchrony in fact determined the perceptual interpretation of the stimulus. Modulations of neural synchronization in the beta-network could not simply be explained by changes in signal power. We first compared power within the identified beta-synchrony network between bounce and pass trials (Figure 3F).