UG thesis presentation

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Predicting specificity of neural activation during cochlear implant stimulationPresented byLuke ZhaoBE/BSc (Bioelectronics, Neuroscience)SupervisorsDr Paul Wong, Dr Paul Carter & A/Prof. Alistair McEwan

The University of SydneyPage #15 s

Good morning everyone. My names Luke and this year Ive been looking at the cochlear implant for the profoundly deaf. In particular, the specificity of neural activation.

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Hearing lossStatisticsAustralia: 1 in 61 (4 million)Worldwide: 360 million2Quality of life3Social isolationMental healthLower employment rate1 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% correctPlateau4Less satisfactory:Music perception5Speech perception with tonal languages6Prosody, 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)


Millions of profoundly deaf miss out on many aspects of life.

Cochlear implants have largely restored speech perception, allowing them to communicate and connect again, which is nothing short of a miracle. However, as this begins to plateau, there are other aspects of hearing yet to be comprehensively addressed.1

CI stimulation & current spread

3. Neural highwayNerve trunk

1. Electrical stimulationElectrode array2. Neural transductionCochlear PartitionOriginal model:Wong (2015)

PeripheralCentral

The University of SydneyPage #17s

At the core of the device, electrodes stimulate neurons to fire signals towards the brain, creating the perception of sound.

One of the challenges is the spread of current, because its not a laser beam and you might stimulate very broadly.2

Specificity in the cochleaTonotopic organisationLike most musical instrumentsSpecificity = hearing resolution?

Cochlear tonotopy.Source: http://www.medel.com/img/c77aa8a6d6c03004f744541102389157.jpg

Photomicrograph of human cochlea.Source: Erixon et al. (2009)

PeripheralCentral

BasalApical


Why might that be a problem? The cochlea is tonotopically organised, which means one end caters for high frequencies and the other end low frequencies.

And if I may take this piano analogy further, the specificity of excitation might be the difference between this, this and that.3

Key questionsHow does current spread in CI stimulation affect neural activity?How does electrode proximity affect current spread?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)

The University of SydneyPage #17 s4

Thesis workflowSTART

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.2KQ.3My workPast workElectrical model of a human neuron & activating function.Source: Rattay et al. (1999)


Ia. Nerve segments

BasalApicalNerve fibre anatomy

Source: Kalkman et al. (2014)

Unrolled cochlea orNode-fibre planePeripheralCentral

Nodes of Ranvier


https://www.youtube.com/watch?v=i30Bv_E0qAU 6

PeripheralCentral

ElectrodesCell bodiesIb. Geometric interpolation


Bipolar+1: E5 (+), E3 (-)

II. Simulations142 simulations = 48 hoursI. Nerve trajectoriesKQ. 2


III. Neural responseVisualisation:Electrode proximity (not to scale)Activation function (AF) valuesPredicted nerve activityAnimated comparisons1frame = 1 configurationBasal to apicalSame current(s)Large side lobes?Electrodes 17-19

PeripheralCentral

BasalApical

KQ.1


III. Neural responseVisualisation:Electrode proximity (not to scale)Activation function (AF) valuesPredicted nerve activityAnimated comparisons1frame = 1 configurationBasal to apicalSame current(s)Large side lobes?Electrodes 17-19

PeripheralCentral

BasalApical

KQ.1


Gfeller et al. (2000)

http://www.soundonsound.com/sound-advice/implanting-awareness

Shapiro et al. (2012)


KQ.3


SpecificityKQ.3MP < BP TP*1-way ANOVA, Tukeys HSDBP < BP+1 < BP+2

MP < pTP(0.33) < pTP(0.67) < TP

Apical activation broaderConsistencies with the literature* Zhu et al. (2012) Snyder et al. (2008) Kalkman et al. (2014)

pTP demo


Assumptions/limitationsThis modelGeometryIntact fibresHomogeneous nerve diameterSimulationQuasi-static assumptionPerfect electrode insertionNeural activationNo neuron degenerationSimple AF threshold

The fieldImaging technologyLive vs cadaveric imagingImage processingPhysiological dataElectrical propertiesNeural activity

The University of SydneyPage #Future stepsRefineGSEF description of ion channelsFrijns et al. (1995)Time-dependent simulationInguva et al. (2015)Minimise manual inputValidatePsychoacousticsExtendNew stimulation configurations?New stimulation waveforms?New electrode arrays?RefineMeDr Paul WongDr Phillip TranProf. Peter Santi & colleagues

The University of SydneyPage #ConclusionsImproved workflow for predicting neural activity from individual cochlea morphology

Electrode proximity current spread breath of neural activitySpecificity: MP < pTP(0.67) < BP+2 < BP+1 < pTP(0.33) < BP < TPSimulation outputs consistent with literatureIdentified possible factor contributing to tinny characteristic of CI hearing

KQ. 1, 2KQ. 3


AcknowledgementsA/Prof. Alistair McEwanDrs Paul Wong, Phillip Tran, Andrian Wong (Bioelectric Modelling Group)Dr Paul Carter, Dr Nick Pawsey, Matt Zygorodimos, A/Prof. Jim Patrick AO (Cochlear Ltd)


ReferencesF. 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. 115142, 2008.B. A. Swanson, Pitch perception with cochlear implants, The University of Melbourne, 2008.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. 341364.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.P. C. H. Wong, High Fidelity Bioelectric Modelling of the Implanted Cochlea, PhD Thesis, The University of Sydney, 2015.E. Erixon et al., Variational anatomy of the human cochlea: Implications for cochlear implantation, Otology and Neurotology, vol. 30, no. 1, pp. 1422, 2009.P. Tran, Investigations of Cochlear Implant Stimulation Using a Finite Element Head Model, PhD Thesis, The University of Sydney, 2015.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. 2338, 2008.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. 620629, 1973.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. 8998, 2014.F. Rattay, The basic mechanism for the electrical stimulation of the nervous system, Neuroscience, vol. 89, no. 2, pp. 335346, 1999.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. 4558, 2012.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. 12, pp. 170186, 1995.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. 426429.

The University of SydneyPage #Questions

The University of SydneyPage #Supplementary

Source: Kalkman et al. (2015)

The University of SydneyPage #Partial tripolar mode

Back to specificityMPTPTPpTP()

The University of SydneyPage #

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2 mm radial proximity from electrode 5



The University of SydneyPage #Node potentials by stimulation mode

Electrode 17 Fibre vs potentialElectrode 11Fibre vs potentialBP+2BP+1BP

VKQ.2Stimulationmode


Node potentials by stimulation mode

Electrode 17 Fibre vs potentialElectrode 11Fibre vs potentialVKQ.2Stimulationmode


The University of SydneyPage #Node potentials by stimulation mode

E17 NF-plane vs potentialE17 Fibre vs potentialE11Fibre vs potential

The University of SydneyPage #AF maps by electrode (synchronised)

TPpTP (0.67)pTP (0.33)MPBPBP+1BP+2


AF maps by electrode (not synchronised)TPpTP (0.67)pTP (0.33)MPBPBP+1BP+2

The University of SydneyPage #Specificity: one-way ANOVA + Tukeys HSD


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Literature CI modesThe originalMonopolar (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 axisStimulus level

The University of SydneyPage #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 cochleaLumped element model.Source: Strelioff (1973).

HEATHERHEATHER+Recent addition of detailed cochlea (HEATHER+).Source: Wong et al. (2015).

The University of SydneyPage #Ib. Geometry: nerve trajectoriesDots = redInterpolation (splines) = blue

PeripheralCentral

Step 1Step 2

(connect-the-dots)

ElectrodesCell bodies

The University of SydneyPage #Stimulation mode comparisons

The University of SydneyPage #Questions?Refine

MeDr Paul WongDr Phillip TranProf. Peter Santi & colleagues

Potentials

E11E17Activating function


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