Consciousness often persists even when unresponsiveness occurs. In two experiments involving 76 healthy males, brain activity was measured during varying states of consciousness induced by propofol and dexmedetomidine (n = 39) and during sleep-deprived wakefulness and non-REM sleep (n = 37). Most participants reported internally generated experiences while unresponsive. Key brain regions, including the thalamus and cingulate cortices, were found critical for consciousness, showing consistent activity patterns regardless of anesthetic type or sleep state, highlighting a core network essential for conscious awareness.
Anaesthetic-induced unresponsiveness and non-rapid eye movement (NREM) sleep share similar conscious experiences. In a within-subject study, 39 healthy males received either dexmedetomidine or propofol to induce unresponsiveness, and 37 were later awakened from NREM sleep. Most participants were rousable, with no difference between the two drugs. Lower drug concentrations were linked to being rousable but not to recall of experiences. Of interviews after anaesthesia and sleep, 69.7% and 64.4% included experiences, respectively, with no significant difference in recall. Disconnected dream-like experiences and memory incorporation of the research setting occurred equally often in both states, while awareness was rare. The findings suggest that both states involve disconnected conscious experiences with similar recall frequencies and content.
Anesthesia-induced disconnectedness—unresponsiveness and unawareness of external events—is linked to reduced activity in the thalamus, but not to widespread cortical suppression, which instead reflects drug exposure itself. In a study of 160 healthy men, four anesthetics (propofol, dexmedetomidine, sevoflurane, S-ketamine) or saline placebo were administered at doses designed to make half of subjects unresponsive. Positron emission tomography showed that, for all anesthetics except S-ketamine, lower thalamic metabolic activity distinguished disconnected from connected states. Widespread cortical metabolic suppression occurred in both connected and disconnected subjects compared with placebo, indicating it is necessary but insufficient for loss of consciousness.