Abstracts

Gradual, progressive preictal dynamical convergence among brain regions has been reported in human epilepsy (IEEE TBME 2003; 50; 616-27) and in an animal model of chronic limbic epilepsy (CLE) (Epilepsia 45 (S7): 211-212). We have used a spontaneously seizing animal model of limbic epilepsy to investigate the occurrence of spatiotemporal transitions involving such dynamical convergence among different regions in an epileptogenic brain. We hypothesize that the frequency of these transitions increases progressively from the time of initial insult to the subsequent manifestation of epilepsy., Young adult male Sprague Dawley rats (N=4) were used in the study. The model was developed using chronic hippocampal stimulation (CHS). The animals animals, after allowing sufficient time for recovery from the stimulation procedure,were connected to an automated system that monitored the T-index calculated from short-term maximum Lyapunov exponents estimated from multiple brain regions. A (dynamical convergence (transition) was defined as a drop in T-index value from a preset upper threshold (U[sub]T[/sub]=10) to a lower threshold (L[sub]T[/sub]=2.662). The time leading to the first seizure was divided into blocks of 12 hours and the frequency of transitions in each block was calculated. The null hypothesis is rejected if the regression slope is found to be significantly positive (p [lt] 0.05)., Two out of the four animals developed spontaneous seizures after CHS. The first showed a progressive increase in frequency of spatiotemporal transitions leading up to the first seizure (recording time before seizure[sim]232.9 hrs, slope=0.09, p=0.0005), the second animal showed an abrupt increase in incidence immediately preceding the seizure (recording time before seizure[sim]142.5 hrs, slope=0.07, p=0.0228). No dynamical transitions were observed in the two animals that did not develop spontaneous seizures., These results suggest that spatiotemporal transitions involving convergence of dynamical values among brain regions may be a marker for epileptogenesis., (Supported by NIH grant R01EB002089, Children s Miracle Network, University of Florida Division of Sponsored Research and Development and Department of Veterans Affairs.)