State-Dependent Cortical Unit Activity Reflects Dynamic Brain State Transitions in Anesthesia.

Area of Science:

• Neuroscience
• Anesthesiology
• Computational Neuroscience

Background:

• Brain states under anesthesia are not static and can change spontaneously.
• Cortical unit activity dynamics during these transitions remain poorly understood.

Purpose of the Study:

• To investigate how cortical neuronal spiking and information transfer change with dynamically transitioning brain states under anesthesia.
• To identify distinct brain states associated with anesthetic levels and neuronal activity patterns.

Main Methods:

• Extracellular unit activity was recorded from rat visual cortex using microelectrode arrays.
• Desflurane anesthetic levels were stepwise reduced (6% to 0%).
• Unsupervised machine learning analyzed multiunit spike patterns to identify distinct brain states.

Main Results:

• Five distinct brain states were identified, showing a non-linear relationship with anesthetic concentration.
• A novel desynchronized brain state with high spike variability and EMG activity occurred at 6% desflurane.
• Synchronous fragmentation of neuronal spiking characterized anesthetic-induced unconsciousness, while a paradoxical desynchronized state emerged in deep anesthesia.

Conclusions:

• Anesthetic effects on neuronal firing rate differ from sleep.
• Synchronous, fragmented spiking is a signature of anesthetic-induced unconsciousness.
• The findings challenge the presumed monotonic, dose-dependent anesthetic effect on the brain.