Nonlinear dynamic properties of low calcium induced epileptiform activity

The study of dynamic properties of epileptiform can help understand the mechanism of seizure initiation and synchronization. It would be a useful tool to predict the onset of seizure. In this project, we induced epileptiform activity in rat hippocampal brain slices by reducing [Ca²⁺]₀. The low calcium model of epilepsy is particularly interesting since neurons can synchronize in the absence of synaptic transmission. DC electric fields were applied on the slice to modulate neuronal activity. Lyapunov exponent, global embedding dimension and the local dimension were calculated for two experiment conditions: (1) epileptiform activity formation course: from onset, transition state to completed developed state; (2) in the presence of various level DC electric fields. The global and local dimensions increased rapidly when low calcium induced epileptiform activity was initiated, but it did not change after that, even in the presence of the electric field. The Lyapunov exponent increased during the activity formation process and during application of small, hyperpolarizing electric fields, but decreased when the applied electric field is big enough to partially suppress the activity. These findings suggest that the maximum Lyapunov exponent can be a good method for distinguishing states of the systems and might be important in seizure prediction and control