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1. The University of Sydney Page 0
Predicting specificity
of neural activation
during cochlear
implant stimulation
Presented by
Luke Zhao
BE/BSc (Bioelectronics, Neuroscience)
Supervisors
Dr Paul Wong, Dr Paul Carter & A/Prof.
Alistair McEwan

2. The University of Sydney Page 1
Hearing loss
– Statistics
– Australia: 1 in 61 (4 million)
– Worldwide: 360 million2
– Quality of life3
– Social isolation
– Mental health
– Lower employment rate
1 http://www.and.org.au/pages/disability-
statistics.html
2
http://www.who.int/mediacentre/factsheets/fs300/en/
3 http://hearforyou.com.au/statsandresearch/
– Speech perception
– ~80% correct
– Plateau4
– Less satisfactory:
– Music perception5
– Speech perception with
tonal languages6
– Prosody, emotion7
Speech perception scores.
Source: Zeng et al. (2008)
The cochlear implant (CI)
4 Zeng et al. (2008)
5 Swanson (2008)
6 Xu et al. (2012)
7 Chatterjee et al. (2015)

3. The University of Sydney Page 2
CI stimulation & current spread
3. Neural
highway
Nerve
trunk
1. Electrical
stimulation
Electrode
array
2. Neural
transduction
Cochlear
Partition
Original model:
Wong (2015)
Peripheral
Central

4. The University of Sydney Page 3
Specificity in the cochlea
– Tonotopic organisation
– Like most musical instruments
– Specificity = hearing resolution?
Cochlear tonotopy.
Source:
http://www.medel.com/img/c77aa8a6d6c03
004f744541102389157.jpg
Photomicrograph of human cochlea.
Source: Erixon et al. (2009)
Peripheral
Central
BasalApical

5. The University of Sydney Page 4
Key questions
1. How does current spread in CI stimulation affect
neural activity?
2. How does electrode proximity affect current spread?
3. How do common CI stimulation modes compare in
terms of excitation specificity?
– Monopolar (MP)
– Bipolar (BP, BP+1, BP+2)
– Tripolar (TP, pTP)
Monopolar, bipolar & tripolar stimulation modes.
Source: adapted from Tran et al. (2015)

6. The University of Sydney Page 5
Thesis workflow
I. Nerve
geometry
II.
Electrical
response
III. Neural
response
STAR
T
Nerve fibre morphology.
Source: Kalkman et al. (2014)
Nerve trajectories of a
guinea pig cochlea.
Source: Wong (2015)
Detailed FEM human
cochlea.
Source: Wong et al.
(2015).
Cochlear implant stimulation modes.
Source: adapted from Tran et al. (2015)
FEM of the whole head.
Source: Tran et al.
(2015)
KQ.1KQ.2
KQ.3
MyworkPastwork
Electrical model of a human
neuron & activating function.
Source: Rattay et al. (1999)

7. The University of Sydney Page 6
Ia. Nerve segments
BasalApical
Nerve fibre
anatomy
Source: Kalkman et al.
(2014)
“Unrolled cochlea”
or
“Node-fibre plane”
Peripheral
Central
Nodes
of
Ranvier

8. The University of Sydney Page 7
Electrode
s
Cell
bodies
Ib. Geometric interpolation

9. The University of Sydney Page 8
Bipolar+1: E5 (+), E3 (-)
II. Simulations
142 simulations = 48 hours
I. Nerve trajectories
KQ. 2

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III. Neural response
– Visualisation:
– Electrode proximity (not to
scale)
– Activation function (AF)
values
– Predicted nerve activity
– Animated comparisons
– 1frame = 1 configuration
– Basal to apical
– Same current(s)
– Large side lobes?
– Electrodes 17-19
Peripheral
Central
Basal Apical
KQ.
1

11. The University of Sydney Page 10
III. Neural response
– Visualisation:
– Electrode proximity (not to
scale)
– Activation function (AF)
values
– Predicted nerve activity
– Animated comparisons
– 1frame = 1 configuration
– Basal to apical
– Same current(s)
– Large side lobes?
– Electrodes 17-19
Peripheral
Central
Basal Apical
KQ.
1

12. The University of Sydney Page 11
Gfeller et al. (2000)
http://www.soundonsound.com/sound-advice/implanting-awareness
Shapiro et al. (2012)

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KQ.
3

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Specificity
KQ.
3
– MP < BP ≈ TP*
– 1-way ANOVA, Tukey’s HSD
– BP < BP+1 < BP+2 †
– MP < pTP(0.33) < pTP(0.67) <
TP‡
– Apical activation broader†
Consistencies with the literature
* Zhu et al. (2012)
† Snyder et al. (2008)
‡ Kalkman et al. (2014)

15. The University of Sydney Page 14
Assumptions/limitations
This model
– Geometry
– Intact fibres
– Homogeneous nerve diameter
– Simulation
– Quasi-static assumption
– Perfect electrode insertion
– Neural activation
– No neuron degeneration
– Simple AF threshold
The field
– Imaging technology
– Live vs cadaveric imaging
– Image processing
– Physiological data
– Electrical properties
– Neural activity

16. The University of Sydney Page 15
Future steps
– Refine
– GSEF description of ion
channels
• Frijns et al. (1995)
– Time-dependent simulation
• Inguva et al. (2015)
– Minimise manual input
– Validate
– Psychoacoustics
– Extend
– New stimulation
configurations?
– New stimulation waveforms?
– New electrode arrays?
Cochlea
imaging
FEM
modelling
Predicting
neural
activity
Clinical
verificatio
n
• Pre-surgical
insights
• Future CI
designs
Refine
Me
Dr Paul Wong
Dr Phillip Tran
Prof. Peter Santi
& colleagues

17. The University of Sydney Page 16
Conclusio
ns
– Improved workflow for predicting neural activity from
individual cochlea morphology
– Electrode proximity → current spread  breath of neural activity
– Specificity: MP < pTP(0.67) < BP+2 < BP+1 < pTP(0.33) < BP <
TP
– Simulation outputs consistent with literature
– Identified possible factor contributing to “tinny”
characteristic of CI hearing
KQ. 1,
2
KQ. 3

18. The University of Sydney Page 17
Acknowledgements
– A/Prof. Alistair McEwan
– Drs Paul Wong, Phillip Tran, Andrian Wong (Bioelectric
Modelling Group)
– Dr Paul Carter, Dr Nick Pawsey, Matt Zygorodimos,
A/Prof. Jim Patrick AO (Cochlear Ltd)

19. The University of Sydney Page 18
References
1. F. G. Zeng, S. Rebscher, W. Harrison, X. Sun, and H. Feng,
“Cochlear implants: system design, integration, and
evaluation,” IEEE The Annual Review of Biomedical
Engineering, vol. 1, pp. 115–142, 2008.
2. B. A. Swanson, “Pitch perception with cochlear implants,” The
University of Melbourne, 2008.
3. L. Xu and N. Zhou, “Tonal Languages and Cochlear
Implants,” in Auditory Prostheses: New Horizons, F.-G. Zeng,
N. A. Popper, and R. R. Fay, Eds. New York, NY: Springer
New York, 2012, pp. 341–364.
4. M. Chatterjee, A. M. Kulkarni, J. A. Christensen, M. L.
Deroche, and C. J. Limb, “Voice emotion recognition and
production by individuals with normal hearing and with
cochlear implants,” Journal of the Acoustical Society of
America, vol. 137, no. 4, p. 2205, 2015.
5. P. C. H. Wong, “High Fidelity Bioelectric Modelling of the
Implanted Cochlea,” PhD Thesis, The University of Sydney,
2015.
6. E. Erixon et al., “Variational anatomy of the human cochlea:
Implications for cochlear implantation,” Otology and
Neurotology, vol. 30, no. 1, pp. 14–22, 2009.
7. P. Tran, “Investigations of Cochlear Implant Stimulation Using
a Finite Element Head Model,” PhD Thesis, The University of
Sydney, 2015.
8. R. L. Snyder, J. C. Middlebrooks, and B. H. Bonham,
“Cochlear implant electrode configuration effects on activation
threshold and tonotopic selectivity,” Hearing Research, vol.
235, no. 1, pp. 23–38, 2008.
9. D. Strelioff, “A computer simulation of the generation and
distribution of cochlear potentials,” The Journal of the
Acoustical Society of America, vol. 54, no. 3, pp. 620–629,
1973.
10. R. K. Kalkman, J. J. Briaire, and J. H. M. Frijns, “Current
focussing in cochlear implants: An analysis of neural
recruitment in a computational model,” Hearing Research, vol.
322, pp. 89–98, 2014.
11. F. Rattay, “The basic mechanism for the electrical stimulation
of the nervous system,” Neuroscience, vol. 89, no. 2, pp. 335–
346, 1999.
12. Z. Zhu, Q. Tang, F.-G. Zeng, T. Guan, and D. Ye, “Cochlear-
implant spatial selectivity with monopolar, bipolar and tripolar
stimulation,” Hearing Research, vol. 283, no. 1, pp. 45–58,
2012.
13. J. H. M. Frijns, S. L. de Snoo, and R. Schoonhoven, “Potential
distributions and neural excitation patterns in a rotationally
symmetric model of the electrically stimulated cochlea,”
Hearing Research, vol. 87, no. 1–2, pp. 170–186, 1995.
14. C. Inguva, P. Wong, A. Sue, A. McEwan, and P. Carter,
“Frequency-dependent simulation of volume conduction in a
linear model of the implanted cochlea,” in 2015 7th
International IEEE/EMBS Conference on Neural Engineering
(NER), pp. 426–429.

20. The University of Sydney Page 19
Questions

21. The University of Sydney Page 20
Supplementary
Source: Kalkman et al. (2015)

22. The University of Sydney Page 21
Partial tripolar mode
σ
1
0
Back to
specificit
y
MP
TP
TP pTP(σ)

23. The University of Sydney Page 22
2 mm radial proximity from electrode 5

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Node potentials by stimulation mode
Electrode 17
Fibre vs potential
Electrode 11
Fibre vs potential
BP+2
BP+1
BP
MP
pTP
2
3
pTP
1
3
TP
V
KQ.
2
Stimulation
mode

27. The University of Sydney Page 26
Node potentials by stimulation mode
Electrode 17
Fibre vs potential
Electrode 11
Fibre vs potential
V
KQ.
2
Stimulation
mode

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29. The University of Sydney Page 28
Node potentials by stimulation mode
E17
NF-plane vs
potential
E17
Fibre vs potential
E11
Fibre vs potential

30. The University of Sydney Page 29
AF maps by electrode (synchronised)
TP
pTP
(0.67)
pTP
(0.33)
MP BP BP+1 BP+2

31. The University of Sydney Page 30
AF maps by electrode (not synchronised)
TP
pTP
(0.67)
pTP
(0.33)
MP BP BP+1 BP+2

32. The University of Sydney Page 31
Specificity: one-way ANOVA + Tukey’s HSD

33. The University of Sydney Page 32
Literature – CI modes
– The original
– Monopolar (MP)
– Higher specificity
– Bipolar (BP/BP+1/BP+2)
– Tripolar (TP)
– Partial tripolar (pTP)
Source: adapted from Tran et al. (2015)
Activity patterns in the brain stem from CI stimulation in the guinea pig.
Source: adapted from Snyder et al. (2008)
Tonotopic axis
Stimuluslevel

34. The University of Sydney Page 33
FEM of the whole head with a focus on the cochlea (Human
Electro-Anatomical Total HEad Reconstruction, “HEATHER”).
Source: Tran et al. (2015)
Literature – models of the cochlea
Lumped element model.
Source: Strelioff (1973).
HEATHERHEATHER+
Recent addition of detailed cochlea (“HEATHER+”).
Source: Wong et al. (2015).

35. The University of Sydney Page 34
Ib. Geometry: nerve
trajectories
Dots = red
Interpolation (splines) = blue
Peripheral
Central
Step 1 Step 2
(connect-the-dots)
Electrod
es Cell
bodie
s

36. The University of Sydney Page 35
Stimulation mode comparisons

37. The University of Sydney Page 36
Questions?
Cochlea
imaging
FEM
modelling
Predicting
neural
activity
Clinical
verificatio
n
• Pre-surgical
insights
• Future CI
designs
Refine
Me
Dr Paul Wong
Dr Phillip Tran
Prof. Peter Santi
& colleagues
Potentials
E1
1
E1
7
Activating function