Neural correlates of consciousness in an auditory no-report fMRI study

In the search for neural correlates of consciousness (NCCs), prominent theories disagree about the role of sensory versus widespread fronto-parietal brain activity. Research on auditory awareness has been widely neglected, and disentangling NCCs from correlates of task-related post-perceptual processes (e.g., report) is an ongoing challenge. In the present study, we addressed these issues using functional magnetic resonance imaging (fMRI) during a no-report inattentional deafness paradigm. Sixty-three healthy human participants performed an auditory distractor task while supra-threshold but task-irrelevant critical sounds were presented in the background. Whereas one group was aware of them, another group remained unaware. Whole-brain responses were analyzed using frequentist and Bayesian inference. During unaware processing, significant activations were restricted to auditory regions in the superior temporal gyrus (STG) and Heschl's gyrus. Aware processing additionally significantly recruited the superior temporal sulcus (STS), the middle temporal gyrus (MTG), and nodes of the ventral and dorsal attention networks. To isolate auditory NCCs, brain responses to the physically identical, task-irrelevant critical sounds were compared between aware and unaware participants, thereby controlling for non-conscious processing while avoiding task-related processing. Auditory awareness was associated with strong, extensive, significant activation in secondary auditory regions (STG, STS, MTG). In comparison, activation in the insula, the inferior, middle, and superior frontal gyrus, as well as the precuneus, was weaker, more spatially confined, and only detected in the Bayesian analysis. These findings suggest a dominant role of stimulus-specific sensory compared to fronto-parietal brain activity in conscious auditory perception.