The Tactile Window to Consciousness is Characterized by Frequency-Specific Integration and Segregation of the Primary Somatosensory Cortex.

Julia Natascha Frey,Nathan Weisz,Markus Siegel,Sabine Leske,Philipp Ruhnau,Christoph Braun

doi:10.1038/srep20805

Abstract

We recently proposed that besides levels of local cortical excitability, also distinct pre-stimulus network states (windows to consciousness) determine whether a near-threshold stimulus will be consciously perceived. In the present magnetoencephalography study, we scrutinised these pre-stimulus network states with a focus on the primary somatosensory cortex. For this purpose participants performed a simple near-threshold tactile detection task. Confirming previous studies, we found reduced alpha and beta power in the somatosensory region contralateral to stimulation prior to correct stimulus detection as compared to undetected stimuli, and stronger event-related responses following successful stimulus detection. As expected, using graph theoretical measures, we also observed modulated pre-stimulus network level integration. Specifically, the right primary somatosensory cortex contralateral to stimulation showed an increased integration in the theta band, and additionally, a decreased integration in the beta band. Overall, these results underline the importance of network states for enabling conscious perception. Moreover, they indicate that also a reduction of irrelevant functional connections contributes to the window to consciousness by tuning pre-stimulus pathways of information flow.

Highlights

Studies investigating pre-stimulus effects in near-threshold (NT) paradigms observed that correctly perceived stimuli are preceded by low alpha power in task-relevant areas
By extending the straightforward interpretation of pre-stimulus effects in terms of local cortical excitability, our framework adds a conceptual contribution to bridge the gap between the pre- and post-stimulus divide
In addition to previously described power decreases in the alpha and beta band in sensory areas prior to conscious perception, here we report for the first time simultaneous functional integration and segregation patterns for the relevant sensory areas

Summary

Introduction

Studies investigating pre-stimulus effects in near-threshold (NT) paradigms observed that correctly perceived stimuli are preceded by low alpha power in task-relevant areas. Despite providing an intuitive explanation of pre-stimulus determinants of conscious perception that are well linked to a strong conceptual framework, this interpretation has a major shortcoming As this viewpoint emphasizes local pre-stimulus cortical excitability, it predicts that successful stimulus detection depends on a bottom-up input sweep. By extending the straightforward interpretation of pre-stimulus effects in terms of local cortical excitability, our framework adds a conceptual contribution to bridge the gap between the pre- and post-stimulus divide (i.e. what would be predicted based on a local excitability hypothesis, and what is observed in the post-stimulus period) It does not predict early activation in sensory regions to determine conscious perception (for detailed argumentation, see[15]). The exact roles, of SI and SII in the window to consciousness have not been explored so far, regarding pre-established functional pathways

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Conclusion