Cochlear implant: From theoretical neuroscience to clinical application

Abstract

Event Abstract Back to Event Cochlear implant: From theoretical neuroscience to clinical application Andreas Bahmer1*, Gerald Langner2, Werner Hemmert3, 4 and Uwe Baumann5 1 Goethe University, Audiological Acoustics, Germany 2 Technical University Darmstadt, Germany 3 Bernstein Center for Computational Neuroscience, Germany 4 Technische Universität München, Institute of Medical Engineering, Germany 5 Goethe University, Germany Cochlear implants are the first and until now the only existing prosthesis that can restore a malfunctioning sensory organ – the inner ear – nearly completely. After implantation and a period of rehabilitation, most previously deaf patients are able to use the telephone or listen to the radio with their cochlear implant system. However, although top performing cochlear implant subjects understand speech nearly perfectly in quiet, large difficulties remain in acoustically complex environments. These difficulties are probably due to the rather artificial electrical stimulation from distinct locations of the electrode. We therefore propose stimulation techniques which account for neurophysiological and neuroanatomical properties not only of the auditory nerve but also of the subsequent cochlear nucleus. The cochlear nucleus shows a variety of cells that combine different encoding mechanisms. Chopper neurons which are the main projecting cells of the ascending subsequent auditory system build an important shunting yard in the cochlear nucleus. The periodicity encoding of those cells is outstanding throughout the cochlear nucleus because they represent frequency tuning and periodicity at the same time by integration of broadband input [1].We have carried out simulations of a physiologically inspired neuronal network including chopper neurons. In our simulation, chopper neurons receive input from both auditory nerve fibers and onset neurons [2,3]. With this topology, the model has the advantage of explaining the large dynamic range of periodicity encoding of chopper neurons in combination with their narrow frequency tuning. Like the models investigated previously, the present model is able to simulate interspike intervals of spike trains of the chopper responses with high precision [3]. Moreover, the simulation can explain essential properties of real chopper neurons by an additional input from onset neurons. Simulations show that variations of the integration widths of onset neurons results in corresponding variations of the spectral resolution and periodicity encoding of chopper neurons [3,4]. Physiological evidence supports our assumption that periodicity information coded by chopper neurons is conveyed via onset neurons [1]. These simulations gave rise for a test of a new stimulation paradigm for cochlear implants.To investigate the influence of the width of the area of stimulation on the accuracy of temporal pitch encoding, synchronous multi-electrode stimulation with biphasic electrical pulse trains was compared to single-electrode stimulation. Temporal pitch discrimination performance was determined by means of a 2-AFC experiment in human cochlear implant subjects at different base rates (100, 200, 283, 400, 566 pps) in both conditions (single- vs. multi-electrode). Overall performance deteriorated with increasing base rate. Although multi-electrode parallel stimulation showed significantly improved pitch discrimination in some subjects at certain base rates, no general enhancement compared to single electrode performance appeared. We will discuss whether the entrainment of the auditory nerve spike pattern to electrical pulsatile stimulation is responsible for the lack of pitch discrimination benefit in the multi-electrode parallel condition.