Intracortical impedance changes during spreading depression

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Abstract
Specific impedance at various depths in the cerebral cortex of the rat was measured using a newly developed thin film coaxial microelectrode. This novel electrode has the advantage of measuring specific impedance of extremely small volumes of tissue, and thus of making highly localized measurements.The resting level of cortical impedance in the rat was found to be stable, but to vary for different sites and animals from 200–700 ohm‐cm. During spreading depression, loop‐shaped impedance loci were consistently observed in the complex impedance plane with peak magnitude 2–3 times resting level. These unusual loop‐shaped loci are thought to represent distinct process differences during development and recovery phases of spreading depression.This preliminary investigation has demonstrated the feasibility of a technique for making highly localized impedance measurements in nervous tissue. Such measurements are useful for in vivo studies of such tissue parameters as extracellular space.