Comparative Study of Terminal Cortical Potentials Using Iridium and Ag/AgCl Electrodes

Area of Science:

• Neuroscience
• Electrophysiology
• Brain Injury Research

Background:

• Brain ischemia causes cortical voltage shifts, including spreading depolarization (SD) and negative ultraslow potentials (NUPs), as markers of brain injury.
• Electrode material and placement significantly influence the recorded features of SD and NUP.

Purpose of the Study:

• To compare terminal cortical events during anesthetic euthanasia using iridium (Ir) and silver/silver chloride (Ag/AgCl) electrodes.
• To investigate the differences in recording spreading depolarization (SD) and negative ultraslow potentials (NUPs) between electrode types.

Main Methods:

• Utilized intracortical linear iridium electrode arrays and Ag/AgCl-based electrodes in the rat somatosensory cortex.
• Recorded cortical electrical activity during isoflurane or sevoflurane euthanasia, monitoring hyperpolarization, SD, and NUPs.

Main Results:

• Both electrode types detected hyperpolarization, SD, and an early NUP phase post-anesthetic-induced respiratory arrest.
• Ag/AgCl electrodes recorded bell-shaped NUPs that diminished within 30 minutes.
• Iridium electrodes recorded biphasic NUPs, including the early phase and a late, progressive depolarizing shift reaching -100 mV over two hours, with greater amplitude in deeper cortical layers.

Conclusions:

• Intracortical Ag/AgCl and Ir electrodes reliably detect early brain injury markers like hyperpolarization, SD, and early NUP.
• The late, large-amplitude NUP phase observed exclusively with Ir electrodes suggests sensitivity to an unidentified factor associated with brain death.