Noninvasive electrodes for electrocochleography in the chinchilla
K. C. Campbell, K. M. Faloon and L. P. Rybak
Division of Otolaryngology, Southern Illinois University School of Medicine, Springfield 62794-9230.
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.(ABSTRACT TRUNCATED AT 250 WORDS)
