Neural and receptor cochlear potentials obtained by transtympanic electrocochleography in auditory neuropathy.
OBJECTIVE
Transtympanic electrocochleography (ECochG) was recorded bilaterally in children and adults with auditory neuropathy (AN) to evaluate receptor and neural generators.


METHODS
Test stimuli were clicks from 60 to 120dB p.e. SPL. Measures obtained from eight AN subjects were compared to 16 normally hearing children.


RESULTS
Receptor cochlear microphonics (CMs) in AN were of normal or enhanced amplitude. Neural compound action potentials (CAPs) and receptor summating potentials (SPs) were identified in five AN ears. ECochG potentials in those ears without CAPs were of negative polarity and of normal or prolonged duration. We used adaptation to rapid stimulus rates to distinguish whether the generators of the negative potentials were of neural or receptor origin. Adaptation in controls resulted in amplitude reduction of CAP twice that of SP without affecting the duration of ECochG potentials. In seven AN ears without CAP and with prolonged negative potential, adaptation was accompanied by reduction of both amplitude and duration of the negative potential to control values consistent with neural generation. In four ears without CAP and with normal duration potentials, adaptation was without effect consistent with receptor generation. In five AN ears with CAP, there was reduction in amplitude of CAP and SP as controls but with a significant decrease in response duration.


CONCLUSIONS
Three patterns of cochlear potentials were identified in AN: (1) presence of receptor SP without CAP consistent with pre-synaptic disorder of inner hair cells; (2) presence of both SP and CAP consistent with post-synaptic disorder of proximal auditory nerve; (3) presence of prolonged neural potentials without a CAP consistent with post-synaptic disorder of nerve terminals.


CONCLUSIONS
Cochlear potential measures may identify pre- and post-synaptic disorders of inner hair cells and auditory nerves in AN.
Santarelli
Rosamaria
R
Department of Medical and Surgical Specialities, Service of Audiology and Phoniatrics, University of Padua, Via Giustiniani 2, I-35128 Padua, Italy. rosamaria.santarelli@unipd.it
Starr
Arnold
A
Michalewski
Henry J
HJ
Arslan
Edoardo
E
D000222:Adaptation, Physiological / Q000502:physiology; D000293:Adolescent; D000328:Adult; D001300:Audiometry, Evoked Response; D001304:Auditory Diseases, Central / Q000503:physiopathology*; D002648:Child; D002675:Child, Preschool; D003051:Cochlea / Q000503:physiopathology*; D003056:Cochlear Nerve / Q000503:physiopathology*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D005260:Female; D006198:Hair Cells, Auditory / Q000502:physiology*; D006320:Hearing Tests; D006801:Humans; D008297:Male; D008875:Middle Aged