zoltán somogyvári hungarian academy of sciences, kfki research institute for particle and nuclear...
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Zoltán Somogyvári
Hungarian Academy of Sciences,KFKI Research Institute for Particle and Nuclear Physics
Department of Biophysics
A model-based approach to the cortical dynamics
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Analysis of cortical dynamics via evoked epilepsy:
Altering the dynamics with pharmacological agents on a
more-or-less known way. Analysis of spatio-temporal
dynamics of the evoked seizure.
Chapter 1
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Local field potential during seizure
An experimental epilepsy model:seizure evoked by 4-Aminopyridin.
6s10s
24s
3 phases, based on typical waveshape and frequency.
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Data analysis: Wavelet transformation
0 8 16 24 32 40 48 56 64
50
40
30
20
10
0
Time (s)
Fre
quen
cy (
Hz)
Am
plit
ude
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A simple modell of cortical micro-circuits and populational dynamics
Four populations of McCulloch-Pitts type neuron models
Depressing excitatory and non-depressing inhibitory synapses
Noise on the input
Random or topographicconnections between populations
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The behaviour of the model: recurrent seizures and the dynamical attractors
The synaptic depression drives the system from the slowing fully activated regime to regime of the irregular or chaotic oscillation.
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Parameter dependence of dynamics
Changeing the relative force of excitation and inhibition, - epileptiform spikes- complex seizures- status epilepticuscould be obtained
Seizures could be eliminated by increasing the strengthof the inhibition
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Comparison of the measured and the simulated pseudo-attractors
Simulated
Measured
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Three epileptogen drug
4-aminopyridin (4AP): blocks K+-channels and increases thesynaptic transmission
bicuculin (BMI): GABA-receptor blocker, inhibits the inhibition
Mg2+-free solution (MFR): Eliminates the Mg2+ blockades of the NMDA-receptors, thus strenghtens theexcitatory synapses
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Measurement of spatio-temporal potential patterns by micro-electrode systems
1.5
mm
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In electrolyte volume conductor the potential satisfies the Poisson-equation
Potentials are driven by Poisson-equation
2 r Ir
E r r
J(r)=E(r)I r J rLow frequency approximation:
Ohm's law:Continuity equation:
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Spatio temporal dynamics of epileptic spikes evoked by 4-
AP
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Spatio temporal dynamics of epileptic spikes evoked by BIC
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Spatio temporal dynamics of epileptic spikes evoked by
MFR
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Characteristic features of the current source density maps
Common features in all three type :
A strong source in the IVth lamina
A large sink from the top of the VI.th lamina to the Vth lamina
Late components with small amplitudes
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Characteristic differences between the three CSD maps
Typical differences:
4AP: simple structure,
BMI: strong sink in the III. lamina
MFR: A large sink in the VI. lamina