Ultrahigh Field fMRI Reveals Different Roles of the Temporal and Frontoparietal Cortices in Subjective Awareness

Whether conscious perception is an all-or-none or a gradual phenomenon depends on the brain region involved. In a 7T fMRI study, participants performed an emotion discrimination task under continuous flash suppression. Recognition sensitivity increased linearly with stimulus awareness, and threat stimuli slowed heart rate during near-clear perception. Brain activity in occipitotemporal, parietal, and frontal regions and the amygdala increased with awareness, while early visual areas showed the opposite pattern. Temporal area activity best fit a gradual model, whereas frontoparietal activity fit a dichotomous model. Specific experimental decisions, such as stimulus type and awareness evaluation method, significantly influence findings in consciousness research.

Study at a glance

Abstract

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 the occipitotemporal, parietal, and frontal regions as well as in the 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 frontoparietal areas fitted a dichotomous model. Furthermore, our findings illustrate 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.