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Brain-State Dependent Perception: Finding the Windows to Consciousness

Final Report Summary - WIN2CON (Brain-State Dependent Perception: Finding the Windows to Consciousness)

The fact that our brain can produce conscious states has captured the imagination of scientists and the public alike for centuries. Since this question is too broad and complex to be answered in a definitive manner, neuroscientists have commonly opted for a more tractable approach by searching for so-called Neural Correlates of Consciousness. Applying this approach e.g. to experiments in which sensory stimuli are matched to threshold for perceptual report (so-called near threshold paradigms) or in which sensory stimuli can yield alternative categorial perceptions (so-called bistable paradigms), has yielded important insights. In particular it showed that conscious perception was accompanied by increased neural activity in relevant sensory as well as fronto-parietal regions following the stimulation. However, in a relatively independent line of research, neuroscientists also discovered that excitability in task-relevant sensory regions was already increased prior to the stimulation. To fill this conceptual gap, between postimulus NCCs and putative prestimulus predispositions, we developed a framework that we labeled "Windows to Consciousness" (Win2Con). The crucial assumption within this framework was that distinct patterns of integration of relevant sensory regions into a distributed neural network at prestimulus periods will determine their influence on downstream processing regions, ultimately leading to perceptual reports. In order to test our framework we largely relied on methods that can non-invasively measure neural activity at a large spatial scale in healthy humans at a fine temporal resolution (Magnetoencephalography, MEG) and their combination with electrical neurostimulation techniques, that can putatively modify neural states in a desired direction. These methods were applied to conventional near-threshold and bistable paradigms, as mentioned above. The main outcomes generated by the project were:

1. Next to prestimulus locally-expressed levels of neural excitability, integration of relevant sensory regions into distributed cortical networks shapes upcoming conscious perception. This provides an important link between pre- and poststimulus differences in conscious perception experiments, that have been the original motivation for the Win2Con framework.
2. Our framework is also causally supported by electrical neurostimulation experiments, in particular the illustration that long-range effects are driven by the magnitude of network integration of brain regions in the vicinity of the stimulation site. Beside of the direct relevance for the project, this effect has far reaching consequences for attempts to understand and predict the impact of electrical brain stimulation (including clinical applications).
3. We have provided first evidence within the same subjects that neural correlates of conscious perception generalize across different sensory modalities (an assumption usually implicitly made but never directly tested). Importantly, we show that this includes a late (~200-400 ms) broadcasting of information into early sensory regions of putatively task-irrelevent sensory modalities (e.g. when you consciously perceive a visual near-threshold stimulus, your auditory cortex will "know" at this late interval).

Beside of its general impact in advancing our understanding of the neural underpinnings and predispositions of conscious perception our project could have far-reaching implications in better understanding clinical (neural and mental) disorders marked by abnormal sensory perception.