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July 1993

Noninvasive Electrodes for Electrocochleography in the Chinchilla

Author Affiliations

From the Division of Otolaryngology, Southern Illinois University School of Medicine, Springfield.

Arch Otolaryngol Head Neck Surg. 1993;119(7):767-771. doi:10.1001/archotol.1993.01880190063013

• This study compares noninvasive vs invasive electrodes for electrocochleography in chinchillas. Summating potential (SP) amplitude, action potential (AP) amplitude, and AP threshold, recorded with five types of noninvasive electrodes, were compared with simultaneous bulla recordings. Noninvasive electrodes included a needle electrode over the bulla, gold Tiptrode (Etymotic Research, Elk Grove Village, Ill), Enhancer I (Nicolet Instrument Corp, Madison, Wis), Coats (Lifetech Inc, Austin, Tex) electrode, and a locally constructed tympanic membrane (TM) electrode. Stimuli included 100-microsecond clicks and 6000-Hz tone bursts (with a 1 millisecond rise/fall time and a 5 millisecond plateau). Stimuli were initially presented at 110 dB peak equivalent sound pressure level for the clicks and 100 dB peak equivalent sound pressure level for the tone bursts. Intensity was then decreased in 10-dB decrements until no replicable AP activity was observed. The TM damping for the TM electrode was measured with 0.5,1,2,4, and 6 kHz and click stimuli. The AP was clear and replicable for all electrodes used in the study, although the amplitude was substantially less for the noninvasive electrodes as opposed to the invasive electrode. The invasive electrode provided the largest amplitude SP recording, but SP could generally be clearly recorded with the needle electrode, Enhancer I, and the Coats electrode. The TM electrode and gold Tiptrode provided SP recordings less consistently. The AP threshold could be recorded with all the electrodes in the study and was generally within 10 dB of threshold recorded invasively. Electrode variables, including ease of electrode placement and potential injury, were examined. The Tiptrode and Enhancer I electrodes posed relatively few problems during placement. The needle electrode placed over the bulla occasionally caused some subdermal bleeding at the placement site. The Coats electrode was more difficult to place because of the marked bend in the chinchilla ear canal. The TM electrode occasionally perforated the TM. Tympanic membrane damping with this electrode ranged from 0 to 50 dB. Consequently, this electrode would not be recommended for use in the chinchilla unless further improved.

(Arch Otolaryngol Head Neck Surg. 1993;119:767-771)