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Modeling the Auditory Pathway

Research Advisor:

Aditya Mathur

School of Industrial Engineering

Department of Computer Science

Purdue University

Graduate Student:

Alok Bakshi

SERC Showcase, Ball Sate University, November 15-16, 2006Sponsor: National Science Foundation

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Objective

To construct and validate a model of the

auditory pathway to understand the effect of various treatments on children with auditory disorders.

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Background and Problem

Children with some forms of auditory disorders are unable to discriminate rapid acoustic changes in speech.

It has been observed that “auditory training” improves the ability

to discriminate and identify an unfamiliar sound. Computational model desired to reproduce this observation.

A validated model would assist in assessing the impact of disorders in the auditory pathway on brainstem potential. This would be useful for diagnosis. [This appears related to fault diagnosis and tolerance in software systems. It might have an impact on the design of redundant software systems.]

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Methodology

Study physiology of the auditory system. Simulate the auditory pathway by constructing new models,

or using existing models, of individual components along the auditory pathway.

Validate the model against experimental results pertaining to the auditory system.

Mimic experimental results of auditory processing tasks in children with disabilities and gain insight into the causes of malfunction.

Experiment with the validated model to assess the effects of treatments on children with auditory/learning disabilities.

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Characteristics of our approach

Systems, holistic, approach. Detailed versus aggregate models. Explicit modeling of inherent anatomical and

physiological parallelism.

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Progress

Synaptic model is implemented for connection between two neurons

Following (existing) models incorporated for the simulation of the Auditory pathway

Phenomenological model for the response of Auditory nerve fibers

Computational model of the Cochlear Nucleus Octopus Cell

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Brainstem Evoked Auditory Potential

http://www.iurc.montp.inserm.fr/cric/audition/english/audiometry/ex_ptw/e_pea2_ok.gif

http://www.iurc.montp.inserm.fr/cric/audition/english/audiometry/ex_ptw/voies_potentiel.jpg

Normal children

Language impaired children

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Auditory Pathway Modeling

Auditory Nerve fiber model by Zhang et. al.

•Octopus Cell model by Levy et. al.

•Models of other cells being implemented

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K+ ion channel

http://personal.tmlp.com/Jimr57/textbook/chapter3/images/pro5.gif

Outside

Iext

IK INa IL

gK gNa gL

VK VNa VL

C

Inside

( At potential V )4ngg KK =

hmgg NaNa3=( ) ( ) ( ) ( )tIVVgVVgVVg

dt

dVC extLLNaNaKK +−+−+−=

m, n and h depend on V

Hodgkin Huxley Model

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Hodgkin Huxley Model (contd.)

http://www.bbraunusa.com/stimuplex/graphics/low_speed_nerve.jpg

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Auditory Neuron Model

(Zhang et al., 2001)(Heinz et al., 2001)(Bruce et al., 2003)

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Cochlear Nucleus

Consist of 13 types of cells Single cell responses differ based on

# of excitatory/inhibitory inputs Input waveform pattern

Onset response

Buildup response

Input tone

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Octopus Cell

Octopus Cell

Receives excitatory input from 60-120 AN

fibers

AN discharge

rate

Time

Octopus Cell

discharge

rate

TimeLatent period

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Schematic of a typical Octopus Cell

http://www.ship.edu/~cgboeree/neuron.gif

Representative Cell• Has four dendrites

• Receives 60 AN fibers with 1.4 - 4 kHz CF

•Majority of input from high SA fibers, medium SA fibers denoted

by superscript ‘m’

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Octopus Cell Model Simplifications

Four dendrites replaced by a single cylinder Active axon lumped into soma Synaptic transmission delay taken as constant 0.5 ms Compartmental model employed with

15 equal length dendritic compartments 2 equal length somatic compartments

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Octopus Cell Model

2 somatic compartments and 15 dendritic compartments modeled by the same circuit with different parameters

Different number of dendritic compartments depending on number of synapses with AN fibers

Soma Dendrite

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Octopus Cell - Output

The output of the model implemented by Levy et. al. is compared against our model on the right side of the figure for a tone given at CF in figure A

Same comparison is made in figure B but with a tone of different intensity

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Bushy Cell

Bushy Cell

Receives excitatory input from 1-20 AN

fibers

AN spikes

Time

Bushy Cell spikes

TimeLatent period

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Bushy Cell Model

Representative Cell• Has no dendrites and axon

• The soma is equipotential

• Receives 1-20 AN fibers with different characteristic frequency

•Inhibitory inputs ignored in the model

Soma

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Bushy Cell Model Characteristics

As the number and conductance of inputs is varied, the

full range of response seen in VCN Bushy cell are

reproduced

For inputs with low frequency(< 1 kHz), the model

shows stronger phase locking than AN fibers, thus

preserving the precise temporal information about the

acoustic stimuli

The model simulates the spherical bushy cell, but

doesn’t reproduce all characteristics of globular bushy

cell

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Bushy Cell Model - Output

Response of Bushy cell for different number of input AN fibers (N), and synaptic conductance (A)

Fig. A shows the response of our implemented model for N=1 and A= 9.1, while the output obtained by Rothman et. al. is shown in D for same parameter.

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Bushy Cell Model - Output

Similarly for N=5 and A=9.1, our implemented model’s response is shown in B, while response of model by Rothman et. al. is shown in E

Finally, the fig. C shows response of our model for N=1, A=18.2 and the corresponding response of model by Rothman et. al. is shown in fig. F

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Fusiform Cell

Fusiform Cell

Receives different inhibitory inputs from

DCN

AN discharge

rate

Time

Fusiform Cell

discharge

rate

TimeLatent period

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Fusiform Cell Model Exhibit buildup and

pauser response and nonlinear voltage/current relationship

The model simulates the soma of fusiform cell with three K+ and two Na+ voltage dependent ion channels

The model doesn’t take into account the Calcium conductance

Doesn’t model the synaptic inputElectrical model of fusiform

cell

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Fusiform Cell Model Characteristics

Predicts the electrophysiological properties of the fusiform cell by using basic Hodgkin-Huxley equations

Simulates the pauser and buildup response by virtue of intrinsic membrane properties

Synaptic organization of cells in DCN is not understood presently, so this model doesn’t model synapse and take direct current as the input instead

Doesn’t rule out the possibility of inhibitory inputs as the reason for pauser and buildup response

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Next Steps Verify the models of Pyramidal and Stellate cell in the

cochlear nucleus. Identify structural connections of different types of cells

in the cochlear nucleus. Modify the models if they ignore few inputs for the sake

of simplification, to account for such inputs. Determine the response of the cochlear nucleus as a

whole with different input waveforms.

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References Hiroyuki M.; Jay T.R.; John A.W. Comparison of algorithms for the

simulation of action potentials with stochastic sodium channels. Annals of Biomedical Engineering, 30:578–587, 2002.

Kim D.O.; Ghoshal S.; Khant S.L.; Parham K. A computational model with ionic conductances for the fusiform cell of the dorsal cochlear nucleus. The Journal of the Acoustical Society of America, 96:1501–1514, 1994.

Levy K.L.; Kipke D.R. A computational model of the cochlear nucleus octopus cell. The Journal of the Acoustical Society of America, 102:391–402, 1997.

Rothman J.S.; Young E.D.; Manis P.B. Convergence of auditory nerve fibers onto bushy cells in the ventral cochlear nucleus: Implications of a computational model. The Journal of Neurophysiology, 70:2562–2583, 1993.

Zhang X.;Heinz M.G.;Bruce I.C.; Carney L.H. A phenomenological model for the responses of auditory-nerve fibers: 1. nonlinear tuning with compression and suppression. The Journal of the Acoustical Society of America, 109:648–670, 2001.

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References

• Drawing/image/animation from "Promenade around the cochlea" <www.cochlea.org> EDU website by R. Pujol et al., INSERM and University Montpellier

• Gunter E. and Raymond R. , The central Auditory System’ 1997

• Kraus N. et. al, 1996 Auditory Neurophysiologic Responses and Discrimination Deficits in Children with Learning Problems. Science Vol. 273. no. 5277, pp. 971 – 973

• Purves et al, Neuroscience 3rd edition• P. O. James, An introduction to physiology of hearing 2nd

edition• Tremblay K., 1997 Central auditory system plasticity:

generalization to novel stimuli following listening training. J Acoust Soc Am. 102(6):3762-73