Evoked Alpha Power is Reduced in Disconnected Consciousness During Sleep and Anesthesia

Area of Science:

• Neuroscience
• Cognitive Science
• Sleep Medicine

Background:

• Conscious experience is altered during sleep and anesthesia, leading to unconsciousness or disconnected consciousness (e.g., dreaming).
• Cortical activity distinguishes conscious from unconscious states, but differences in disconnected states remain less understood.
• Alpha activity is implicated in regulating sensory perception.

Purpose of the Study:

• To investigate differences in evoked cortical activity between states of disconnected consciousness and wakefulness.
• To determine if alpha activity is altered in disconnected states like REM sleep and ketamine anesthesia.
• To identify potential biomarkers for sensory disconnection.

Main Methods:

• Utilized transcranial magnetic stimulation-electroencephalography (TMS-EEG) over parietal regions.
• Recorded evoked oscillatory activity during wakefulness, REM sleep, NREM sleep, and ketamine/propofol anesthesia.
• Correlated electrophysiological findings with dream reports obtained during NREM sleep awakenings.

Main Results:

• Evoked alpha power (8-12 Hz) was decreased during disconnected consciousness (REM sleep, ketamine anesthesia) compared to wakefulness.
• Evoked low-gamma power (30-40 Hz) was decreased in unconscious states (NREM sleep, propofol anesthesia) versus wakefulness or disconnected states.
• Findings were consistent with dream reports from NREM sleep.

Conclusions:

• Suppression of evoked alpha activity is a potential marker for sensory disconnection.
• Distinct patterns of altered oscillatory activity characterize different states of consciousness.
• TMS-EEG provides insights into neural signatures of altered awareness during sleep and anesthesia.