Presentation title Presentation sub-title
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.
0
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)
The University of SydneyPage #20 s
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
The University of SydneyPage #17 s
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)
The University of SydneyPage #55 s5
Ia. Nerve segments
BasalApicalNerve fibre anatomy
Source: Kalkman et al. (2014)
Unrolled cochlea orNode-fibre planePeripheralCentral
Nodes of Ranvier
The University of SydneyPage #12 s
https://www.youtube.com/watch?v=i30Bv_E0qAU 6
PeripheralCentral
ElectrodesCell bodiesIb. Geometric interpolation
The University of SydneyPage #8 s7
Bipolar+1: E5 (+), E3 (-)
II. Simulations142 simulations = 48 hoursI. Nerve trajectoriesKQ. 2
The University of SydneyPage #15 s8
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
The University of SydneyPage #35 s9
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
The University of SydneyPage #35 s10
Gfeller et al. (2000)
http://www.soundonsound.com/sound-advice/implanting-awareness
Shapiro et al. (2012)
The University of SydneyPage #30 s11
KQ.3
The University of SydneyPage #17 s12
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
The University of SydneyPage #45 s13
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
The University of SydneyPage #30 s16
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)
The University of SydneyPage #15 s17
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 #
21
2 mm radial proximity from electrode 5
The University of SydneyPage #
The University of SydneyPage #
The University of SydneyPage #Node potentials by stimulation mode
Electrode 17 Fibre vs potentialElectrode 11Fibre vs potentialBP+2BP+1BP
VKQ.2Stimulationmode
The University of SydneyPage #17 s25
Node potentials by stimulation mode
Electrode 17 Fibre vs potentialElectrode 11Fibre vs potentialVKQ.2Stimulationmode
The University of SydneyPage #17 s26
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
The University of SydneyPage #
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
The University of SydneyPage #
31
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
The University of SydneyPage #