Luis De Vera

Reptilian waking EEG: slow waves, spindles and evoked potentials

Signal spectral analysis procedures were used to compute the power spectrum of Gallotia galloti lizards EEG at different (5-35 degrees C) body temperatures. EEG power spectra were mainly characterized by a low frequency peak between 0.5 and 4 Hz which was present at the different body temperatures. A second spectral peak, corresponding to spindles of similar pattern to the sleep spindles of mammals, also appears in the spectra. The peak frequency of the spindles increased with the body temperature. Flash evoked potentials were characterized by a slow triphasic component upon which a spindle was superimposed, adopting a morphology similar to the K complexes of mammalian sleep. The characteristics of this EEG and evoked potentials support the hypothesis of homology between the waking state of the reptiles and the slow wave sleep of mammals.

Assessment of electroencephalographic functional connectivity in term and preterm neonates

OBJECTIVE To study how functional connectivity of neonate EEG during sleep is assessed by different interdependence indices and to analyze its dependence on conceptional (CA), gestational (GA) and/or chronological age (CRA). METHODS EEG data from eight cortical regions were recorded during active (AS) and quiet sleep (QS) in three groups of seven neonates each: preterm (PT; GA: 33-34 weeks; CA: 39-40 weeks), junior-term (JT; GA: 38-39 weeks; CA: 39-40 weeks) and senior-term neonates (ST; GA: 38-39 weeks; CA: 44-45 weeks). EEG functional connectivity was assessed by means of the coherence function (its magnitude (MSC) and its imaginary part (IMC)) and a measure of phase synchronization called phase lag index (PLI). RESULTS Inter-hemispheric connectivity: (a) during AS in the beta band, the MSC of the ST group was greater than that of the PT group for the temporal region; (b) during QS in the delta band, both PLI and IMC of the ST group were different to those of the PT group for the frontopolar and central regions, whereas ST-JT differences were only found for PLI. Intra-hemispheric connectivity: (a) during AS in the beta band the MSC of the ST group was greater than that of the PT group for the left frontopolar-centrotemporal and right occipital-centrotemporal regions; (b) during QS in the beta band, both IMC and PLI were different for the JT group than for the PT and the ST groups for the right and left occipital-centrotemporal regions. CONCLUSIONS EEG inter- and intra-hemispheric functional connectivity in neonates during sleep changes with the CA and CRA in delta and beta bands. SIGNIFICANCE The neonates brain development during the first weeks of life can be traced from changes in the characteristics of EEG functional connectivity.

Evolution of wakefulness, sleep and hibernation: From reptiles to mammals

Thus far, most hypotheses on the evolutionary origin of sleep only addressed the probable origin of its main states, REM and NREM. Our article presents the origin of the whole continuum of mammalian vigilance states including waking, sleep and hibernation and the causes of the alternation NREM-REM in a sleeping episode. We propose: (1) the active state of reptiles is a form of subcortical waking, without homology with the cortical waking of mammals; (2) reptilian waking gave origin to mammalian sleep; (3) reptilian basking behaviour evolved into NREM; (4) post-basking risk assessment behaviour, with motor suspension, head dipping movements, eye scanning and stretch attending postures, evolved into phasic REM; (5) post-basking, goal directed behaviour evolved into tonic REM and (6) nocturnal rest evolved to shallow torpor. A small number of changes from previous reptilian stages explain these transformations.

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

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.

Comparing generalized and phase synchronization in cardiovascular and cardiorespiratory signals

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.

Power spectral analysis of short-term RR interval and arterial blood pressure oscillations in lizard (Gallotia galloti): Effects of parasympathetic blockade☆

Spontaneous short-term oscillations in consecutive beat-to-beat RR interval (RRI) and systolic blood pressure (SBP) values of lizards (Gallotia galloti) in basal conditions and under parasympathetic blockade with atropine at 23°C body temperature were investigated using spectral analysis. In control conditions, both RRI and SBP spectra exhibited two major oscillations in very low (VLF 0.008–0.030 Hz) and low (LF 0.030–0.100 Hz) frequencies. Most lizards presented a high frequency (HF) respiratory peak in the SBP spectra whenever the lizards ventilatory pattern was rhythmic. Parasympathetic blockade decreased all RRI oscillations and LF and HF oscillationsof SBP. VLF and LF oscillations of RRI and SBP were still clearly present after blockade, which shows that other neural or humoral systems different from parasympathetic could mediate also low frequency RRI and SBP variability. SBP-RRI cross-spectral analysis showed in control conditions a linear relationship between SBP and RRI variations in the VLF, LF and HF bands, with SBP variations leading RRI; the parasympathetic limb of the baroreflex seems to be involved in maintaining the SBP-RRI coherence in the LF and perhaps in the HF band.

Non-linear asymmetric interdependencies in the electroencephalogram of healthy term neonates during sleep.

The multichannel electroencephalograph (EEG) of six healthy term neonates was recorded during awake as well as during active and quiet sleep. The existence and nature of the interdependencies among the different brain areas were studied by means of a multivariate variant of the surrogate data method. Such interdependencies were then quantified by using the coherence function and a newly developed non-linear index. The results showed that during quiet sleep these interdependencies were mostly non-linear, asymmetric and greater than those found during both awake and active sleep. We conclude that the index might be useful to define patterns of EEG interdependencies in healthy neonates, thereby allowing the early detection of brain dysfunctions.

Performance analysis of univariate and multivariate EEG measurements in the diagnosis of ADHD

OBJECTIVE To investigate the performance of univariate and multivariate EEG measurements in diagnosing ADHD subjects in a broad age range. METHODS EEG from eight cortical regions were recorded at rest during eyes open and eyes closed in 22 male ADHD subjects of combined type and 21 healthy male controls (age range 4-15 years). Univariate and interdependence measurements calculated from the frequency domain and from the reconstructed state spaces of EEG signals were computed, and their performance in discriminating ADHD from healthy subjects was analyzed. RESULTS Significant between-group differences in univariate measures were age-dependent. However, certain interdependence inter-hemispheric measures during eyes closed showed significant, age-independent between-groups differences. Among them, coherence in the beta band between inter-occipital regions and between left/occipital-right/central regions provided an overall accuracy classification rate of 74.4%. Even greater accuracy (86.7%) was obtained by an interdependence index of generalized synchronization between left/occipital-right/central regions and left/central-right/temporal regions. CONCLUSIONS EEG beta coherence and especially the degree of generalized synchronization between a few inter-hemispheric regions during resting state with eyes closed allow a high accuracy classification rate of ADHD subjects. SIGNIFICANCE Changes in inter-hemispheric EEG functional brain connectivity at rest are useful for ADHD diagnosis in a broad age range.

Nonlinearity and fractality in the variability of cardiac period in the lizard, Gallotia galloti: effects of autonomic blockade.

Both nonlinear and fractal properties of beat-to-beat R-R interval variability signal (RRV) of freely moving lizards (Gallotia galloti) were studied in baseline and under autonomic nervous system blockade. Nonlinear techniques allowed us to study the complexity, chaotic behavior, nonlinearity, stationarity, and regularity over time of RRV. Scaling behavior of RRV was studied by means of fractal techniques. The autonomic nervous system blockers used were atropine, propranolol, prazosin, and yohimbine. The nature of RRV was linear in baseline and under beta-, alpha(1)- and alpha(2)-adrenoceptor blockades. Atropine changed the linear nature of RRV to nonlinear and increased its stationarity, regularity and fractality. Propranolol increased the complexity and chaotic behavior, and decreased the stationarity, regularity, and fractality of RRV. Both prazosin and yohimbine did not change any of the nonlinear and fractal properties of RRV. It is suggested that 1) the use of both nonlinear and fractal analysis is an appropriate approach for studying cardiac period variability in reptiles; 2) the cholinergic activity, which seems to make the alpha(1)-, alpha(2)- and beta-adrenergic activity interaction unnecessary, determines the linear behavior in basal RRV; 3) fractality, as well as both RRV regularity and stationarity over time, may result from the balance between cholinergic and beta-adrenergic activities opposing actions; 4) beta-adrenergic activity may buffer both the complexity and chaotic behavior of RRV, and 5) neither the alpha(1)- nor the alpha(2)-adrenergic activity seem to be involved in the mediation of either nonlinear or fractal components of RRV.

Ultradian oscillation in the heart rate of rainbow trout (Oncorhynchus mykiss)

Abstract 1. 1. Ultradian oscillations in the min and hr range on long-term (24-hr) computerized recordings of heart rate in rainbow trout Oncorhynchus mykiss , acclimated to 5, 10 and 15°C water temperature, were investigated. Eight-hour duration time series derived from the heart rate recordings were analysed for their harmonic content in the ultradian band by spectral analysis. 2. 2. A significant ultradian rhythm at around 0.011 cycles/min (approximately 91-min period) was detected in the power spectral density functions of all the 8-hr duration time series derived from the heart rate recordings at the three experimental water temperatures. 3. 3. The spectral power of the ultradian oscillation detected in heart rate of trout was found to increase significantly with increasing temperature. 4. 4. The possible endogenous origin of the ultradian rhythm detected in heart rate of Oncorhynchus mykiss is discussed.