Characterizing chaotic behavior of REM sleep EEG using Lyapunov exponent

The Lyapunov exponent of the hippocampal EEG was calculated to examine its chaotic behavior. In particular, we study the REM sleep EEG of rats from hippocampal subfields cornu ammonis (CA1) and dentate gyrus (DG) that show prominent theta activity. Our main goal is to characterize, through nonlinear dynamics analysis, the ontogenetic variation between the granule cells of the DG and the pyramidal cells of the CA1 as the animal matures. We examined the hippocampal REM sleep EEG from rats of 15-day and 90-day of age. Our results show that the Lyapunov exponents of the hippocampal REM sleep EEG from both CA1 and DG are positive in 15-day and 90-day age groups, a strong evidence confirming their chaotic behavior. While the estimated Lyapunov exponents of hippocampal REM sleep EEG of CA1 and DG from 90-day rats are similar, the Lyapunov exponents of CA1 and DG from 15-day rats are significantly different.