Abstracts

Rationale: Evidence from animal models and patient data indicate that febrile status epilepticus (FSE) in early development can result in diminished cognitive abilities. To understand the variability in cognitive outcome following FSE, hippocampal EEG measurements were made in three groups of rats, control and FSE animals that were able to learn an active avoidance task and FSE animals that were unable to learn the task.Methods: We compared normalized mean amplitude and mean frequency of local field potentials in layer CA1 in all bandwidths for each of the three groups while foraging for food pellets and during an active avoidance task in order to find putative network differences with and without cognitive demands placed on the animal. We also compared normalized voltage correlations between hippocampal layers CA1 and CA3 as well as the preferred phase of firing within the theta cycle for cells in each region during foraging sessions.Results: Significant differences in local field potentials during foraging and avoidance were found in FSE learners whom exhibited a mean slow gamma frequency that was slower than controls and FSE non-learners. Compared to controls and FSE learners, FSE non-learners exhibited the fastest theta frequency during foraging but the slowest theta frequency during the avoidance task. While there were no apparent group differences with regard to preferred phase of firing of cells in CA3, CA1 cells in FSE learners were more likely to be phase-locked between 90-150° of local theta rhythm. Theta band voltage cross-correlations between CA1 and CA3 for FSE non-learners were much lower than FSE learners and controls.Conclusions: We hypothesize that the differences found in FSE learners with regard to CA1 LFPs and preferred firing phase for CA1 cells reflect a form of physiological compensation in hippocampal networks. We hypothesize that these alterations in hippocampal circuit function underlie differences in cognitive outcome following FSE.