Propofol-induced Unresponsiveness Is Associated with a Brain Network Phase Transition

Area of Science:

• Neuroscience
• Complex Systems
• Anesthesiology

Background:

• The human brain operates near criticality, enabling flexible state coordination.
• Anesthesia is known to disrupt electroencephalogram (EEG) waveform criticality.
• The impact of anesthesia on brain network connectivity criticality remains less understood.

Purpose of the Study:

• To investigate the hypothesis that propofol anesthesia induces abrupt, divergent changes in brain network connectivity across frequencies and time scales.
• To characterize these changes as a potential phase transition, indicative of lost criticality.

Main Methods:

• Analyzed 31-channel EEG data from 16 volunteers receiving propofol.
• Calculated functional connectivity using phase and amplitude metrics (1-20 Hz) across millisecond to minute time scales.
• Assessed network global efficiency, clustering coefficient, and statistical complexity, comparing with a Kuramoto network model.

Main Results:

• Propofol-induced anesthesia showed critical slowing and decreased global network efficiency for 2 Hz power envelope metrics (long time scales).
• Conversely, global network efficiency increased for the 10 Hz weighted phase lag index (phase-based connectivity).
• Network complexity decreased significantly for both hypersynchronous (10 Hz) and asynchronous (2 Hz) states, mirroring a phase transition.

Conclusions:

• Propofol anesthesia triggers a brain network phase transition around the loss of behavioral responsiveness.
• This transition involves a collapse of long-time scale connectivity and an increase in phase-based connectivity.
• Findings support the concept of anesthesia-induced loss of criticality in brain network dynamics.