Abstract
In cognitive neuroscience, prerequisites of consciousness are of high interest. Within recent years it has become more commonly understood that ongoing brain activity, mainly measured with electrophysiology, can predict whether an upcoming stimulus is consciously perceived. One approach to investigate the relationship between ongoing brain activity and conscious perception is to conduct near-threshold (NT) experiments and focus on the pre-stimulus period. The current review will, in the first part, summarize main findings of pre-stimulus research from NT experiments, mainly focusing on the alpha band (8–14 Hz). It is probable that the most prominent finding is that local (mostly sensory) areas show enhanced excitatory states prior to detection of upcoming NT stimuli, as putatively reflected by decreased alpha band power. However, the view of a solely local excitability change seems to be too narrow. In a recent paper, using a somatosensory NT task, Weisz et al. (2014) replicated the common alpha finding and, furthermore, conceptually embedded this finding into a more global framework called “Windows to Consciousness” (Win2Con). In this review, we want to further elaborate on the crucial assumption of “open windows” to conscious perception, determined by pre-established pathways connecting sensory and higher order areas. Methodologically, connectivity and graph theoretical analyses are applied to source-imaging magnetoencephalographic data to uncover brain regions with strong network integration as well as their connection patterns. Sensory regions with stronger network integration will more likely distribute information when confronted with weak NT stimuli, favoring its subsequent conscious perception. First experimental evidence confirms our aforementioned “open window” hypothesis. We therefore emphasize that future research on prerequisites of consciousness needs to move on from investigating solely local excitability to a more global view of network connectivity.
Highlights
Consciousness is one of the main enigmas of philosophy and has always been of great interest to experimental psychology
Since advancing a mechanistic understanding of how phenomenological states emerge from neural activity patterns appears not currently feasible, a popular strategy in cognitive neuroscience has been to first identify the so-called neural correlates of consciousness (NCC), defined as “the minimal set of neural events that give rise to a specific aspect of a conscious percept” (Crick and Koch, 1998)
RESEARCH QUESTIONS In the current review we gave an overview of previous work regarding factors determining conscious perception with a focus on oscillatory alpha modulations prior to NT stimulation
Summary
Consciousness is one of the main enigmas of philosophy and has always been of great interest to experimental psychology. Electrophysiological research found ongoing brain activity in the alpha range preceding upcoming stimuli that can predict whether the stimulus can be reported (i.e., consciously accessed) or not (e.g., Hanslmayr et al, 2007; van Dijk et al, 2008).
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