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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
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
Local field potential during seizure
An experimental epilepsy model:seizure evoked by 4-Aminopyridin.
6s10s
24s
3 phases, based on typical waveshape and frequency.
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
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
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.
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
Comparison of the measured and the simulated pseudo-attractors
Simulated
Measured
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
Measurement of spatio-temporal potential patterns by micro-electrode systems
1.5
mm
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:
Spatio temporal dynamics of epileptic spikes evoked by 4-
AP
Spatio temporal dynamics of epileptic spikes evoked by BIC
Spatio temporal dynamics of epileptic spikes evoked by
MFR
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
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