NeuroPSI – Paris-Saclay University

Investigating the evoked responses in the primary auditory cortex obtained by electrical stimulations through a cochlear implant

Abstract
Cochlear implant, which restores hearing in cases of severe or profound deafness, is the most widely used neuroprosthesis in the world today. An increase in the number of implanted subjects should be expected in the future due to general aging and increase in noise pollution. Although the implanted subjects can have a good understanding of speech in silence, their understanding is usually poor in noisy environments. Considerable technical improvements and the search for objective measures are therefore necessary, making animal models mandatory for this purpose.
This thesis aims at studying the responses of cortical neurons during the use of different shapes of electrical pulses: the rectangular biphasic pulse, classically used in clinic and four shapes of biphasic ramped pulses, the first phase of these pulse was either anodic or cathodic.

With each ramped pulse, we observed:
(i) an increase in the cortical neurons maximum firing rate,
(ii) a decrease in response threshold,
(iii) a lower level of injected charge to reach the maximum firing rate,
(iv) no significant change in dynamic range,
(v) a decrease in response latencies as a function of the increase in injected charge and
(vi) a higher reproducibility compared to a rectangular pulse. Furthermore, when comparing the response to electrical stimulations and to acoustic stimulations, we showed that
(vii) neuronal firing rate was unchanged,
(viii) latencies were lower with electrical stimulation and
(viii) there was no difference in temporal reproducibility.
The use of ramped pulses in cochlear implants will be a promising strategy to explore in the incoming years.

Jury Members

• • Tania Barkat, Rapportrice (University of Basel, Suisse)
  • Daniel Pressnitzer, Rapporteur (LSP, Université Paris Sciences & Lettres)
  • Valérie Ego-Stengel, Examinatrice (NeuroPSI, Université Paris Saclay )
  • Micaela Galante, Examinatrice (NeuroPSI, Université Paris Saclay)
  • Olivier Macherey, Examinateur (LMA, Université Aix Marseille)

and

• Jean-Marc Edeline (Institut NeuroPSI, Saclay)