Frequency synchronization reveals that spike-wave discharges in wag/rij rats are significantly nonlinear phenomenon

In this work, we studied the time-frequency dynamics of spike-wave discharges in rats with predisposition to absence epilepsy (WAG/Rij line) in two frequency ranges: 7-12Hz and 14-24Hz. The first and the second harmonics of the seizure main frequency lie in these ranges. Recordings of brain local field potentials of eight animals in eleven experiments of eight hour duration were analyzed. The method was based on the fast Fourier transform with a Hann's window, and skeletons were constructed based on the obtained spectrograms. Using the skeletons, a visual and automated numerical assessment of the main frequency evolution was performed. As a result of this analysis, it was shown that temporal dynamics of the main frequency in the range 14-24Hz follows the dynamics of the main frequency in the range 7-12Hz. Since during the baseline activity the main frequencies in two considered ranges were developing independently, our finding indicates that the discharge is a significantly nonlinear process.