A reduced level of consciousness affects non-conscious processes

Summary

Sedation with Propofol alters non-conscious brain processes as much as conscious ones, challenging the assumption that anesthetics selectively suppress consciousness. By manipulating both the content (conscious vs. non-conscious perception) and level (arousal via sedation) of consciousness during fMRI, the authors found that these two aspects are dissociable. This suggests that level and content of consciousness are separate phenomena, prompting a re-evaluation of what it means to be conscious.

Study at a glance

Abstract

Being conscious is a profound aspect of human existence, and understanding its function and its inception is considered one of the truly grand scientific challenges. However, the nature of consciousness remains enigmatic, to a large part because “being conscious” can refer to both the content (phenomenology) and the level (arousal) of consciousness, and how these different aspects are related remains unclear. To empirically assess the relation between level and content of consciousness, we manipulated these two aspects by presenting stimuli consciously or non-consciously and by using Propofol sedation, while brain activity was measured using fMRI. We observed that sedation greatly affected non-conscious processes, which starkly contrasts the notion that anesthetics selectively reduce consciousness. Our findings reveal that level and content of consciousness are separate phenomena, and imply that one may need to reconsider what “being conscious” means.