Heart rate telemetry records of up to 5 days duration were obtained from pike living in Lochs Kinord and Davan, Scotland. Applying metabolic rate correlations it was found that mean metabolic rate (R) was 1.5 times standard metabolic rate (It?), The fish rarely worked near their metabolic limits. Activity metabolism (RJ was much higher than estimates based on mean swimming speed and comprised up to 10% of R. Most activity metabolism was the result of localized bursts of activity. Less than 10% of activity showed evidence of oxygen debt. Specific Dynamic Action or feeding metabolism (R,) comprised 15-25% of R. Food intake estimated from heart rate was 1.5% wet body weight day-', consumed in the form of small items captured during the day and digested during the afternoon and night.

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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 (λ1)] were calculated, and EEG spectrum and fractal exponent β 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, λ1 ∼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 λ1. 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.

We made use of multivariate nonlinear analysis methods to study the interdependence between the cardiac interval variability and both the respiratory activity and the systolic pressure in rats. The study was carried out in basal conditions and after the application of different drugs affecting the cardiovascular system. The results showed that there are changes both in the extent and in the directionality of such interdependences because of the drugs. The inhibition of the NO and the parasympathetic blockade changed the cardiovascular coordination, with the latter one also modifying the interdependence between the cardiac interval and the respiratory signal. This suggests that the nonlinear approach might be very helpful to explore the interaction between subsystems of the cardiovascular control system.

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This work aims at assessing the maturational changes in the interdependence between the activities of different cortical areas in neonates during active sleep (AS) and quiet sleep (QS). Eight electroencephalography (EEG) channels were recorded in 3 groups of neonates of increasing postmenstrual age. The average linear (AVL) and average nonlinear (AVN) interdependencies of each electrode region with the remaining ones were calculated using the coherence function and a recently developed index of nonlinear coupling between 2 signals in their state spaces, respectively. In theta band, AVL increased with neonate's age for central and temporal regions during QS. In beta band, AVL increased for most cortical regions during QS and a parallel decrease of AVL with neonate's age was found during AS. For all regions, beta AVL was greater in AS than in QS in preterm neonates but the reverse happened in older term neonates. Contrarily to AVL, AVN decreased with age during QS for most cortical regions. Surrogate data test showed that the interdependencies were nonlinear in preterm and younger term neonates but in older term both linear and nonlinear interdependencies coexisted. It is concluded that neonatal maturation is associated with changes in the magnitude and character of the EEG interdependencies during sleep.

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