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. 3 phases, based on typical waveshape and frequency.

Data analysis: Wavelet transformation Time (s) Frequency (Hz) Amplitude

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 topographic connections 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 epilepticus could be obtained Seizures could be eliminated by increasing the strength of 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 Mg 2+ -free solution (MFR):Eliminates the Mg 2+ blockades of the NMDA-receptors, thus strenghtens the excitatory synapses

Measurement of spatio-temporal potential patterns by micro-electrode systems

In electrolyte volume conductor the potential satisfies the Poisson-equation Potentials are driven by Poisson-equation J(r)=  E(r) Low 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 IV th lamina A large sink from the top of the VI. th lamina to the V th 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