Nonlinear, fractal, and spectral analysis of the EEG of lizard, Gallotia galloti

Electroencephalogram (EEG) from dorsal cortex of lizard Gallotia galloti wa s analyzed at different temperatures to test the presence of fractal or non linear structure during open (OE) and closed eyes (CE), with the aim of com paring these results with those reported for human slow-wave sleep (SWS). T wo nonlinear parameters characterizing EEG complexity [correlation dimensio n (D2)] and predictability [largest Lyapunov exponent (lambda(1))] were cal culated, and EEG spectrum and fractal exponent beta were determined via coa rse graining spectral analysis. At 25 degrees C, evidence of nonlinear stru cture was obtained by the surrogate data test, with EEG phase space structu re suggesting the presence of deterministic chaos (D2 similar to 6, lambda( 1) similar to 1.5). Both nonlinear parameters were greater in OE than in CE and for the right hemisphere in both situations. At 35 degrees C the evide nce of nonlinearity was not conclusive and differences between states disap peared, whereas interhemispheric differences remained for lambda(1). Harmon ic power always increased with temperature within the band 8-30 Hz, but onl y with OE within the band 0.3-7.5 Hz. Qualitative similarities found betwee n lizard and human SWS EEG support the hypothesis that reptilian waking cou ld evolve into mammalian SWS.