Vol. 277, Issue 1, R86-R93, July 1999
Nonlinear, fractal, and spectral analysis of the EEG of
lizard, Gallotia
galloti
Julián
González1,
Antoni
Gamundi2,
Rubén
Rial2,
M. Cristina
Nicolau2,
Luis
de
Vera1, and
Ernesto
Pereda1
1 Laboratorio de
Biofísica, Departamento de Fisiología, Facultad de
Medicina, Universidad de La Laguna, 38320 Tenerife; and
2 Laboratorio de
Fisiología, Departamento de Biología Fundamental y
Ciencias de la Salud, Universidad de las Islas Baleares, 07071 Mallorca, Spain
Electroencephalogram (EEG) from dorsal cortex of lizard
Gallotia
galloti was analyzed at different
temperatures to test the presence of fractal or nonlinear structure
during open (OE) and closed eyes (CE), with the aim of comparing these
results with those reported for human slow-wave sleep (SWS). Two
nonlinear parameters characterizing EEG complexity [correlation
dimension (D2)] and predictability
[largest Lyapunov exponent
(
1)] were calculated,
and EEG spectrum and fractal exponent 
were determined via coarse
graining spectral analysis. At 25°C, evidence of nonlinear structure was obtained by the surrogate data test, with EEG phase space
structure suggesting the presence of deterministic chaos (D2 ~6,
1 ~1.5). Both nonlinear
parameters were greater in OE than in CE and for the right hemisphere
in both situations. At 35°C the evidence of nonlinearity was not
conclusive and differences between states disappeared, whereas
interhemispheric differences remained for
1. Harmonic power always
increased with temperature within the band 8-30 Hz, but only with
OE within the band 0.3-7.5 Hz. Qualitative similarities found
between lizard and human SWS EEG support the hypothesis that reptilian
waking could evolve into mammalian SWS.
correlation dimension; largest Lyapunov exponent; fractal exponent; harmonic power; reptile telenchephalic activity
