title: Response profiles of murine spiral ganglion neurons on multi-electrode arrays.
abstract: OBJECTIVE
  Cochlear implants (CIs) have become the gold standard treatment for deafness. These neuroprosthetic devices feature a linear electrode array, surgically inserted into the cochlea, and function by directly stimulating the auditory neurons located within the spiral ganglion, bypassing lost or not-functioning hair cells. Despite their success, some limitations still remain, including poor frequency resolution and high-energy consumption. In both cases, the anatomical gap between the electrode array and the spiral ganglion neurons (SGNs) is believed to be an important limiting factor. The final goal of the study is to characterize response profiles of SGNs growing in intimate contact with an electrode array, in view of designing novel CI devices and stimulation protocols, featuring a gapless interface with auditory neurons.
  
  
  METHODS
  We have characterized SGN responses to extracellular stimulation using multi-electrode arrays (MEAs). This setup allows, in our view, to optimize in vitro many of the limiting interface aspects between CIs and SGNs.
  
  
  RESULTS
  Early postnatal mouse SGN explants were analyzed after 6-18 days in culture. Different stimulation protocols were compared with the aim to lower the stimulation threshold and the energy needed to elicit a response. In the best case, a four-fold reduction of the energy was obtained by lengthening the biphasic stimulus from 40 μs to 160 μs. Similarly, quasi monophasic pulses were more effective than biphasic pulses and the insertion of an interphase gap moderately improved efficiency. Finally, the stimulation with an external electrode mounted on a micromanipulator showed that the energy needed to elicit a response could be reduced by a factor of five with decreasing its distance from 40 μm to 0 μm from the auditory neurons.
  
  
  CONCLUSIONS
  This study is the first to show electrical activity of SGNs on MEAs. Our findings may help to improve stimulation by and to reduce energy consumption of CIs and thereby contribute to the development of fully implantable devices with better auditory resolution in the future.
authors.affiliation: Inner Ear Research Laboratory, University Departments of Clinical Research and Otorhinolaryngology, Head & Neck Surgery, Inselspital, University of Bern, Switzerland. Regenerative Neuroscience Cluster, Department of Clinical Research, University of Bern, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Hahnewald
authors.forename: Anne
authors.initials: A
authors.lastname: Tscherter
authors.forename: Emanuele
authors.initials: E
authors.lastname: Marconi
authors.forename: Jürg
authors.initials: J
authors.lastname: Streit
authors.forename: Hans Rudolf
authors.initials: HR
authors.lastname: Widmer
authors.forename: Carolyn
authors.initials: C
authors.lastname: Garnham
authors.forename: Heval
authors.initials: H
authors.lastname: Benav
authors.forename: Marcus
authors.initials: M
authors.lastname: Mueller
authors.forename: Hubert
authors.initials: H
authors.lastname: Löwenheim
authors.forename: Marta
authors.initials: M
authors.lastname: Roccio
authors.forename: Pascal
authors.initials: P
authors.lastname: Senn
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D003054:Cochlear Implants; D004599:Electric Stimulation Therapy / Q000295:instrumentation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D051379:Mice; D008810:Mice, Inbred C57BL; D046228:Microarray Analysis / Q000295:instrumentation*; D008839:Microelectrodes; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013136:Spiral Ganglion / Q000166:cytology* / Q000502:physiology*