Local wakefulness-like activity of layer 5 cortex under general anaesthesia

Area of Science:

• Neuroscience
• Anesthesiology
• Consciousness Studies

Background:

• Consciousness is typically lost during general anesthesia, with recent theories linking unconsciousness to widespread brain synchrony in specific neurons.
• The interplay between global and local brain states, including local wakefulness, is not fully understood in the context of general anesthesia.

Purpose of the Study:

• To investigate whether local wakefulness in specific cortical neurons is compatible with deep general anesthesia.
• To test the hypothesis that global synchrony of layer 5 cortical neurons is a necessary condition for anesthesia-induced unconsciousness.

Main Methods:

• Utilized chemogenetics to unilaterally activate layer 5 pyramidal neurons in the sensorimotor cortex of isoflurane-anesthetized mice.
• Monitored local brain activity for state transitions and assessed the level of unconsciousness and interhemispheric synchrony.

Main Results:

• Chemogenetic activation induced local wakefulness-like activity (tonic firing) in the targeted hemisphere without altering the depth of anesthesia.
• This local wakefulness disrupted interhemispheric synchrony but did not reduce unconsciousness or affect transitions into or out of anesthesia.
• Global layer 5 synchrony appears sufficient, but not necessary, for isoflurane-induced unconsciousness.

Conclusions:

• Local wakefulness-like activity in layer 5 cortical neurons can be maintained under deep general anesthesia.
• Global layer 5 synchrony is not a necessary condition for anesthesia-induced unconsciousness, challenging existing models.
• Findings encourage further research into the complex local and global dynamics underlying anesthesia and consciousness.