Electroencephalographic signals during anesthesia recorded from surface and depth electrodes

Area of Science:

• Neuroscience
• Anesthesiology
• Biophysics

Background:

• Anesthesiologists increasingly use electroencephalography (EEG)-based indexes to assess unconsciousness levels.
• The underlying physiology and biophysics of EEG monitoring during anesthesia remain poorly understood.

Purpose of the Study:

• To investigate the biophysical principles of EEG monitoring in anesthesia.
• To understand how EEG signals generated during anesthesia are recorded by surface and depth electrodes.

Main Methods:

• Recorded EEG from scalp and deep brain stimulation (DBS) electrodes.
• Employed mathematical modeling with a realistic head model to analyze electrode montage sensitivity.

Main Results:

• Anesthesia-induced EEG patterns, like burst-suppression, generate voltage gradients detectable throughout the head.
• EEG currents form closed loops, flowing from the cortex surface and returning via the brain's base and skull.
• Standard anesthesia monitoring electrodes are most sensitive to the basal frontal lobes and frontal/mesial temporal lobes.

Conclusions:

• EEG signals during anesthesia are volume-conducted throughout the entire head.
• Understanding EEG current flow explains the detectability of anesthesia patterns by both surface and depth electrodes.