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Weisz N, Wühle AD, Monittola G, Demarchi G, Frey J, Popov T, Braun C (2014) Prestimulus oscillatory power and connectivity patterns predispose conscious somatosensory perception. Proceedings of the National Academy of Sciences USA, 111(4):E417-425    
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Experimental use of near-threshold stimuli is regarded as an important approach to study neural processes leading to conscious access (defined in operational terms as “reportability”). Looking to what extent prestimulus periods contribute to the variability of perceptual states has become increasingly popular, frequently pointing to an increased excitability of relevant sensory regions. Here, we aim to extend this “local” perspective by a network approach. A framework called “Windows to Consciousness” is introduced. We postulate that along with an enhanced excitability, preestablished pathways of information flow are a crucial ingredient, determining whether an upcoming near-threshold stimulus will be consciously perceived. Using magnetoencephalography combined with state-of-the-art source-imaging approaches, we are able to report supportive evidence
Abstract
Which aspects of our sensory environment enter conscious awareness does not only depend on physical features of the stimulus, but also critically on the so-called current brain state. Results from magnetoencephalography/EEG studies using near-threshold stimuli have consistently pointed to reduced levels of α- (8–12 Hz) power in relevant sensory areas to predict whether a stimulus will be consciously perceived or not. These findings have been mainly interpreted in strictly “local” terms of enhanced excitability of neuronal ensembles in respective cortical regions. The present study aims to introduce a framework that complements this rather local perspective, by stating that the functional connectivity architecture before stimulation will predetermine information flow. Thus, information computed at a local level will be distributed throughout a network, thereby becoming consciously accessible. Data from a previously published experiment on conscious somatosensory near-threshold perception was reanalyzed focusing on the prestimulus period. Analysis of spectral power showed reduced α-power mainly in the contralateral S2 and middle frontal gyrus to precede hits, thus overall supporting the current literature. Furthermore, differences between hits and misses were obtained on global network (graph theoretical) features in the same interval. Most importantly, in accordance with our framework, we could show that the somatosensory cortex is “more efficiently” integrated into a distributed network in the prestimulus period. This finding means that when a relevant sensory stimulus impinges upon the system, it will encounter preestablished pathways for information flow. In this sense, prestimulus functional connectivity patterns form “windows” to conscious perception