Pre-stimulus Microstates and Bodily Signals Independently Influence Perceptual Awareness at the Discrimination Threshold.

Perceptual awareness of threshold or multi-stable stimuli varies with the pre-stimulus global state of the brain as indexed by EEG microstates. Similarly, awareness also varies with cyclic fluctuations of visceral signals across the cardiac and the respiratory cycle. It remains to be investigated whether the momentary state of the brain contributes to awareness jointly or independently of the bodily phase. We used an orientation discrimination task to determine to what degree the subjective awareness of a visual threshold stimulus varied with the pre-stimulus microstate, cardiac and respiratory phase and whether the brain and body exerted a joint or independent influence on fluctuations of subjective awareness. We compared the pre-stimulus EEG microstates preceding correct aware and unaware trials for the cardiac and respiratory phase. Our findings indicate that the canonical Microstate D was more prevalent in the unaware compared to the aware condition, and the canonical Microstate A accounted for more variance during inhalation compared to exhalation. The pre-stimulus activation of Microstate D, which is anticorrelated with attentional networks preceded trials in which the stimulus was not perceived. Inhalation was instead associated with Microstate A, suggesting increased arousal during this phase. However, we observed no interaction between the bodily phase and awareness, suggesting that the states of the brain and the body exert independent influence on perceptual awareness at the discrimination threshold.