The origin of electrophonic activity evoked by electrical stimulation of the cochlea
AuthorShepherd, R. K.; Maffi, C. L.; Clark, Graeme M.
Source TitleProceedings of the Australian Neuroscience Society
Document TypeConference Item
CitationsShepherd, R. K., Maffi, C. L., & Clark, G. M. (1992). The origin of electrophonic activity evoked by electrical stimulation of the cochlea. In Proceedings of the Australian Neuroscience Society, Adelaide, S.A.
Access StatusOpen Access
This is an abstract of a paper from Proceedings of the Australian Neuroscience Society 1992 published by Australian Neuroscience Society. This version is reproduced with the permission of publisher.
Electrophonic activation of auditory nerve fibres via electrical stimulation is only observed in cochleas with residual hair cells. While the generation of neural activity associated with this phenomenon is thought to ultimately occur at the inner hair cell synapse (1) it is unclear whether hair cells are activated directly by the electrical stimulus or mechanically via a travelling wave propagating along the basilar membrane. Support for the travelling wave hypothesis has recently come from a masking study using evoked potentials (2). To provide verification of these results, we measured the latency of the electrophonic activity recorded in single ventral cochlear nucleus (VCN) units of known characteristic frequency (CF). Stimulating electrodes were placed on, or just inside the round window of normal hearing anaesthetized cats (n=6). The response of single VCN units were recorded extracellularly and units exhibiting "primary like" activity (3) were analysed. Each unit's CF to acoustic stimulation and response properties to biphasic electric pulses were determined. Electrophonic activity was identified by its long latency (> 2.5 ms) and poor synchronization compared with the response evoked by direct electrical stimulation. Electrophonic activity was observed in 20 units -approximately 25% of the units isolated. These responses were more commonly recorded from cochleas in which the round window had not been opened. The latency of the electrophonic response varied inversely with CF, implying that the response is generated at the basilar membrane and results in a mechanical travelling wave. Finally, no electrophonic activity was observed in units with CFs greater than 10 kHz. Our data would predict that the latency of electrophonic activity in these units -if present -would be very short. Presumably its absence is a result of refractoriness within auditory nerve fibres following activity evoked by direct electrical stimulation.
Keywordsotolaryngology; electrical stimulation; electrophonic activity
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