Harmonic analysis of nerve impedance in situ

A novel technique to assess electric activity of the whole nerve in situ is advanced based on harmonic analysis of impedance microvariations of femoral nerve in narcotized rats recorded with extracellular electrodes. The amplitude spectrum of nerve bioimpedance (Z-spectrum) made it possible to determine the level of neural asynchronous activity in the frequency band of 20–600 Hz with amplitude resolution of 1% and to reveal the rhythmic activity at Mayer (0.1 Hz) and respiration frequencies with amplitude resolution of 0.1%. Systemic administration of atropine used to shift the sympathovagal balance in favor of sympathetic system increased both rhythmic and unrhythmic (asynchronous) neural activity. The study demonstrated that harmonic analysis of nerve bioimpedance is a novel and potent tool to assess neural activity in the frequency domain.