Measurement of temporal interaction due to neural dynamics with cochlear implants
-
1
Technische Universität München, Bio-Inspired Information Processing, IMETUM, Germany
In cochlear implants (neuroprosthesis for deaf) the auditory nerve is stimulated directly by electrical pulses. The general shortcoming of electrical stimulation is field spread and results in channel interaction. The independent information transmission to the brain is limited as the channels are not well separated which leads to poor frequency resolution and impaired speech understanding in noise. In this context the trend to encode auditory signals by low numbers of frequency channels but high stimulation pulse-rates arises the question: how good is the temporal resolution?To determine temporal interaction of electrical stimulation in humans, we measured the influence of a sub-threshold pre-pulse with fixed charge on the perception threshold of a subsequent probe pulse. The inter pulse distance IPD between pre-pulse and probe varied between 20µs to 20 ms to evaluate temporal interaction. The fixed charge of the pre-pulse was 80 % of threshold of the single pulse. The polarity of the two pulses covered all 4 possible cases. The electric stimulation was applied directly to the implant devices by the research interface box RIB II. The biphasic pulses had the parameters: phase width = 40 µs, inter-phase gap = 30 µs and stimulus rate = 4 Hz.In this study we tested 11 subjects (age ± std: 50,1 ± 13,9) with MED-EL PulsarCI100 device implanted for more than 1 year. We measured at two electrodes, one middle (6) and one apical (1). The experiment was in accordance with the ethical Declaration of Helsinki 1975 (clinic rechts der Isar vote no. 2126/08.The result of our measurements is that the temporal interaction leads to a threshold reduction of the probe pulse in all cases. This threshold reduction effect was significant up to 600 µs and in some subjects even interaction effects up to 1 ms were seen. The interaction effect was largest for small IPIs. Here it reaches up to 35 % ± 6% threshold reduction in relation to the single pulse threshold. The threshold reduction effect size depended on the polarity of pre-pulse and probe pulse. When both pulses had the same polarity the effect was smaller than if the pulses have different polarities.We suggest that this temporal interaction effect results from neuronal dynamics. The sub-threshold stimulation shifts the potential of the spiral ganglions. This shift out of resting state ,which depends on the polarity of the stimulation pulse influences the activation of the ion channels. The shift from the resting state is nonlinear, relaxation reaches long durations and causes temporal interactions.Concluding, we can say that significant temporal interaction on sub-threshold pulses occurs up to 600 µs, which is relevant in actual coding strategies because the inter pulse distances are often shorter. For CIS strategies the effects of field spread and channel interaction lead to even shorter IPIs between channels.Our results show that it is important in coding strategies to predict and correct not only simultaneous interactions but also temporal interactions.
Acknowledgements
Bernsteinzentrum for Computational Neuroscience München, MED-EL Innsbruck, Inst. für Ionenphysik und Angewandte Physik, Universität Innsbruck und Klinikum rechts der Isar HNO München
Keywords:
computational neuroscience
Conference:
Bernstein Conference on Computational Neuroscience, Berlin, Germany, 27 Sep - 1 Oct, 2010.
Presentation Type:
Presentation
Topic:
Bernstein Conference on Computational Neuroscience
Citation:
Karg
S,
Lackner
C and
Hemmert
W
(2010). Measurement of temporal interaction due to neural dynamics with cochlear implants.
Front. Comput. Neurosci.
Conference Abstract:
Bernstein Conference on Computational Neuroscience.
doi: 10.3389/conf.fncom.2010.51.00133
Copyright:
The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers.
They are made available through the Frontiers publishing platform as a service to conference organizers and presenters.
The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated.
Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed.
For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions.
Received:
24 Sep 2010;
Published Online:
24 Sep 2010.
*
Correspondence:
Dr. Sonja Karg, Technische Universität München, Bio-Inspired Information Processing, IMETUM, Munich, Germany, karg@tum.de