Ultrahigh field fMRI reveals different roles of temporal and fronto-parietal cortices in subjective awareness

A central question in consciousness theories is whether one is dealing with a dichotomous ("all-or-none") or a gradual phenomenon. In this 7T fMRI study we investigated whether dichotomy or gradualness in fact depends on the brain region associated with perceptual awareness reports. Both male and female human subjects performed an emotion discrimination task (fear vs neutral bodies) presented under continuous flash suppression with trial-based perceptual awareness measures. Behaviorally, recognition sensitivity increased linearly with increased stimuli awareness and was at chance level during perceptual unawareness. Physiologically, threat stimuli triggered a slower heart rate than neutral ones during 'almost clear' stimulus experience, indicating freezing behavior. Brain results showed that activity in occipito-temporal, parietal and frontal regions as well as in amygdala increased with increased stimulus awareness while early visual areas showed the opposite pattern. The relationship between temporal area activity and perceptual awareness best fitted a gradual model while the activity in fronto-parietal areas fitted a dichotomous model. Furthermore, our findings demonstrate that specific experimental decisions, such as stimulus type or the approach used to evaluate awareness, play pivotal roles in consciousness studies and warrant careful consideration.