Abstracts

Rationale: Neuronal populations in the brain achieve levels of synchronous electrophysiological activity as a consequence of both normal brain function as well as during pathological states such as in epileptic seizures. Understanding the nature of this synchrony and the dynamics of neuronal oscillators in the brain is a critical component towards decoding such complex behaviors. We sought to achieve a more in-depth understanding of the dynamics underlying the evolutions of seizures in limbic epilepsy by analyzing recordings of local field potentials (LFPs) from three subcortical nuclei that are part of the circuit of Papez in a kainic acid (KA) rat model of temporal lobe epilepsy. Methods: Recurring spontaneous seizures were induced in six male Sprague-Dawley rats via microinjection of KA (20?l) in the focal hippocampus. LFPs were recorded from the focal hippocampus, contralateral hippocampus, and anteromedial thalamus of the rats. These recordings were analyzed using the empirical mode decomposition (EMD) technique. EMD allows for an adaptive and non-linear decomposition of the local field potentials into a series of finite oscillatory components. We calculated the frequencies, power, and measures of phase synchrony of these oscillatory components as spontaneous seizures evolved in the brain. Results: During a seizure, we observed a convergence of the frequencies of the various oscillatory components along with an increase in their average power. We also discovered patterns of high frequency transient phase synchrony in which the frequency of synchronization and specific brain structures involved varied between the stages of seizure initiation and natural termination. Conclusions: The spatio-temporal dynamics of phase synchrony obtained in this research may provide insight for both increased understanding of the mechanisms underlying limbic epilepsy and improved clinical management of the disease.