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