Factoring the brain signatures of anesthesia concentration and level of arousal across individuals

• It is debated if thalamo-cortical or fronto-parietal circuits induce consciousness.
• We measured functional connectivity of awake and propofol-sedated healthy subjects.
• We factored out effects of drug concentration and arousal level of the participants.
• Fronto-parietal loops are related only to drug concentration in blood.
• In contrast, thalamic connectivity indexes individual’s level of arousal.

Combining resting-state functional magnetic resonance imaging (fMRI) connectivity and behavioral analysis during sedation, we factored out general effects of the anesthetic drug propofol and a specific index of conscious report, participants’ level of responsiveness. The factorial analysis shows that increasing concentration of propofol in blood specifically decreases the connectivity strength of fronto-parietal cortical loops. In contrast, loss of responsiveness is indexed by a functional disconnection between the thalamus and the frontal cortex, balanced by an increase in connectivity strength of the thalamus to the occipital and temporal regions of the cortex.