Mourad Akaârir

University of the Balearic Islands, Palma, Balearic Islands, Spain

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Publications (21)77.99 Total impact

  • [Show abstract] [Hide abstract] ABSTRACT: Unilateral sleep in marine mammals has been considered as a defence against airway obstruction, as a sentinel for pod maintenance, and as a thermoregulatory mechanism. Birds also show asymmetric sleep, probably to avoid predation. The variable function of asymmetric sleep suggests a general capability for independence between brain hemispheres. Patients with obstructive sleep apnea share similar problems with diving mammals, but their eventual sleep asymmetry received little attention. The present report shows that human sleep apnea patients also present temporary interhemispheric variations in dominance during sleep, with significant differences when comparing periods of open and closed airways. The Magnitude of Squared Coherence, an index of interhemispheric EEG interdependence in phase and amplitude rises in the delta EEG range during apneic episodes, while the Phase Lag Index, a measure of linear and non-linear interhemispheric phase synchrony, drops to zero. The L index, which measures generalized nonlinear EEG interhemispheric synchronization, increases during apneic events. Thus, the three indexes show significant and congruent changes in interhemispheric symmetry depending on the state of the airways. In conclusion, when confronted with a respiratory challenge, sleeping humans undergo small but significant breathing-related oscillations in interhemispheric dominance, similar to those observed in marine mammals. The evidence points to a relation between cetacean unihemispheric sleep and their respiratory challenges.
    No preview · Article · Nov 2012 · AJP Regulatory Integrative and Comparative Physiology
  • No preview · Article · Dec 2011 · Sleep Medicine Reviews
  • [Show abstract] [Hide abstract] ABSTRACT: Five Wistar rats were surgically implanted with cortical and parietal electrodes for conventional polysomnography to test for sleep-related EEG asymmetries during 48 hours of continuous recording. When the animals were grouped not according to right-left dominance (which would represent a population bias) but instead according to preferred vs non-preferred hemisphere, significant light/dark circadian changes in side dominance were found in delta power during NREM; in theta and beta power during REM; and in alpha 1, alpha 2, and theta power during wakefulness. The changes have been interpreted as a response to temporal variations in the capability to respond to environmental challenges.
    No preview · Article · May 2011 · Laterality
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    [Show abstract] [Hide abstract] ABSTRACT: 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.
    Full-text · Article · Jul 2010 · Neuroscience & Biobehavioral Reviews
  • R.V. Rial · M. Akaârir · A. Gamund · M.C. Nicolau · S. Esteban
    [Show abstract] [Hide abstract] ABSTRACT: The evolution of sleep has been the subject of several studies and reviews (Allison & Cicchetti, 1976; Allison & Van Twyver, 1970; Hartse, 1994; Karmanova, 1982; Meddis, 1983; Monnier, 1980; Tauber, 1974). However, corresponding studies on the evolution of wakefulness have been fewer (Esteban, Nicolau, Gamundí, et al., 2005; Nicolau, Akaârir, Gamundí, et al., 2000), despite a number of reasons supporting the greater importance of waking in animal adaptation. First of all, waking and sleep are inseparable, an obvious assertion that, notwithstanding, has been ignored in most reviews (see, for instance, Zepelin, 1994; Zepelin & Rechtschaffen, 1974; Zepelin, Siegel, & Tobler, 2005). These reviews compute correlations between the main traits of sleep and ecological variables while forgetting that high correlations of a given trait with total sleep time also imply high correlations with waking time. The present review proposes a change of paradigm from sleep centeredness to waking centeredness. Let us give an example of the paradigm change: there might be two possible viewpoints related to the high danger of a particular species' exposure within an environment, namely: Sleep is a dangerous state. Therefore natural selection must have reduced sleep in dangerous environments. Alertness is necessary to cope with danger. Therefore natural selection must have increased waking time in dangerous environments. The difference between the two alternatives might seem subtle: but the former focuses on sleep as a key adaptive factor, while the latter is waking-centered.
    No preview · Article · Jan 2009
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    [Show abstract] [Hide abstract] ABSTRACT: Letter to Editor
    Full-text · Article · Mar 2008 · Journal of Pineal Research
  • [Show abstract] [Hide abstract] ABSTRACT: The problem of an objective definition of consciousness increases several orders of magnitude when trying to recognize the physical basis of consciousness and the existence of conscious entities different from human beings. A viewpoint proposes that consciousness appeared in response to the need to develop a central control taking behavioral decisions based on motivational, sensory-spatial, and motor circumstances. To make such a decision, the organism should distinguish the sensory changes produced in the environment from those produced as a consequence of its own behavioral output. Some animals can such distinctions only using peripheral controls, while in animals with multiple spatial senses (vision, audition, olfaction, somesthesis) a central unification in form of central motor control is needed to produce a multisensory representation of the environment. A different viewpoint has been proposed, postulating that consciousness is the evolutionary result of sensation, and therefore retains the properties of sensation, that is, quality, intensity, affectivity, and duration. This review tries to develop an evolutionary tree of consciousness. It first discusses which adaptive advantage animals have acquired by consciousness. Behavior of sufficient complexity to consider the existence of consciousness could be found in three groups: arthropods, mollusks and vertebrates. The chapter analyzes the question on the adaptability of consciousness, provides a summary on the empirical proofs supporting (or rejecting) the existence of consciousness in the arthropods and mollusks is provided, examines the existence of consciousness in vertebrates.
    No preview · Article · Dec 2007
  • [Show abstract] [Hide abstract] ABSTRACT: Introduction Our main interest in writing a review on the trivial nature of sleep1 was asserting that the main function of sleep is merely adapting the activity of the organism to the light-dark cyclic changes of the planet but also to confront the triviality of sleep with the non-trivial functions of wakefulness. We are happy to see that our viewpoint has provoked a discussion on many aspects of sleep which in our opinion are taken for granted but actually lack sufficient objective support. We are thus grateful to Rattenborg and co-workers2 for having accepted the invitation to criticize our review. We examine next these criticisms.
    No preview · Article · Oct 2007 · Sleep Medicine Reviews
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    [Show abstract] [Hide abstract] ABSTRACT: Rest in poikilothermic animals is an adaptation of the organism to adjust to the geophysical cycles, a doubtless valuable function for all animals. In this review, we argue that the function of sleep could be trivial for mammals and birds because sleep does not provide additional advantages over simple rest. This conclusion can be reached by using the null hypothesis and parsimony arguments. First, we develop some theoretical and empirical considerations supporting the absence of specific effects after sleep deprivation. Then, we question the adaptive value of sleep traits by using non-coding DNA as a metaphor that shows that the complexity in the design is not a definitive proof of adaptation. We then propose that few, if any, phenotypic selectable traits do exist in sleep. Instead, the selection of efficient waking has been the major determinant of the most significant aspects in sleep structure. In addition, we suggest that the regulation of sleep is only a mechanism to enforce rest, a state that was challenged after the development of homeothermy. As a general conclusion, there is no direct answer to the problem of why we sleep; only an explanation of why such a complex set of mechanisms is used to perform what seems to be a simple function. This explanation should be reached by following the evolution of wakefulness rather than that of sleep. Sleep could have additional functions secondarily added to the trivial one, although, in this case, the necessity and sufficiency of these sleep functions should be demonstrated.
    Full-text · Article · Sep 2007 · Sleep Medicine Reviews
  • [Show abstract] [Hide abstract] ABSTRACT: This commentary is referred to the review signed by Rattemborg [N.C. Rattenborg, Evolution of slow wave sleep and palliopallial connectivity in mammals and birds. A hypothesis. Brain Res. Bull. 69 (2006) 20-29]. We propose that the review missed important aspects in relation to the characteristics of sleep in poikilotherm vertebrates and in the evolution of sleep. Poikilotherms continuously show an EEG dominated by slow waves, but its highest amplitude appears not during sleep, but during active waking. In addition, they show an arousal reaction which consists in an increase in EEG amplitude and synchrony, opposite to mammals and birds. As a consequence, most of the conclusions proposed in the review should be rejected.
    No preview · Article · Jun 2007 · Brain Research Bulletin
  • No preview · Article · Jan 2007
  • No preview · Chapter · Oct 2005
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    [Show abstract] [Hide abstract] ABSTRACT: The adaptive value of sleep remains unknown in spite of the intense research performed throughout the last decades. However, few sleep researchers are aware of the difficulties posed by the blind acceptance of an extreme adaptationist viewpoint. Under this philosophy, every anatomical and functional detail present in a living being should have a positive adaptive value, a position that has been considered as rather doubtful. In this report, it is proposed that most of the physiological changes used for mammalian sleep definition could be mere by-products of other true adaptations, such as the ontogenetic and phylogenetic development of the nervous system. As a result, complex mammalian sleep could have no adaptive value over that of the simplest forms of rest-activity cycles present in all living forms. In addition, it is proposed that the absence of adaptive value should, by default, be the first option regarding the function of sleep. Besides, the burden of the proof should be always charged over the proponents of every particular adaptive function. As this proof has not been reached, it is the absence of function for sleep which should be taken for granted.
    Full-text · Article · Feb 2005 · Medical Hypotheses
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    [Show abstract] [Hide abstract] ABSTRACT: The phenomenological evidence for distinguishing between REM and NREM sleep is overwhelming. However, this difference has only been found thanks to electrophysiological analytical methods, and is practically non existent in phenotypic terms, i.e., observable with the naked eye. It is well accepted that the selective pressure determining evolutionary changes can only work upon phenotypic differences. Hence, it follows that the differences between REM and NREM could not have been selected through evolution and this implies that, in functional terms, both states could be equivalent.
    Full-text · Article · Feb 2003 · Medical Hypotheses
  • R V Rial · M C Nicolau · S Esteban · A Gamundí · M Akaârir
    No preview · Article · Dec 2001 · Sleep
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    M C Nicolau · M Akaârir · A Gamundí · J González · R V Rial
    [Show abstract] [Hide abstract] ABSTRACT: The cause of sleep is a complex question, which needs first, a clear distinction amongst the different meanings of a causal relationship in the study of a given behavior, second, the requisites to be met by a suggested cause, and third, a precise definition of sleep to distinguish behavioral from polygraphic sleep. This review aims at clarifying the meaning of the question and at showing the phylogenetic origin of the mammalian and avian sleep. The phylogenetic appearance of sleep can be approached through a study of the evolution of the vertebrate brain. This began as an undifferentiated dorsal nerve, which was followed by the development of an anterior simplified brain and ended with the formation of the multilayered mammalian neocortex or the avian neostriate. The successive stages in the differentiation of the vertebrate brain produced, at least, two different waking types. The oldest one is the diurnal activity, bound to the light phase of the circadian cycle. Poikilotherms control the waking from the whole brainstem, where their main sensorymotor areas lie. Mammals developed the thalamocortical lines, which displaced the waking up to the cortex after acquiring homeothermy and nocturnal lifestyle. In order to avoid competence between duplicate systems, the early waking type, controlled from the brainstem, was suppressed, and by necessity was turned into inactivity, probably slow wave sleep. On the other hand, the nocturnal rest of poikilotherms most probably resulted in rapid eye movement sleep. The complex structure of the mammalian sleep should thus be considered an evolutionary remnant; the true acquisition of mammals is the cortical waking and not the sleep.
    Full-text · Article · Dec 2000 · Progress in Neurobiology
  • [Show abstract] [Hide abstract] ABSTRACT: Adaptations to survive periods of limited access to oxygen should have been favored along the evolution of vertebrates. Paradigmatic examples of this adaptation are the diving animals, which can sustain prolonged and repetitive periods of anoxia. These animals support what would be considered a severe gas imbalance in their internal environment thanks to three main strategies: increased oxygen stores, resistance to asphyxia, and reduced metabolic expenditure during the apneic intervals. However, diving animals developed their abilities from very old life-sustaining responses that should have been used on many other occasions. Humans with sleep apneas perhaps share many physiological adaptations with diving animals. We review here the extent of such similarities and offer clear evidence of its existence and suggest possible research lines that could improve the clinical knowledge about this condition.
    No preview · Article · Feb 2000 · Sleep And Breathing
  • G Alemany · M Akaârir · A Gamundí · M C Nicolau
    [Show abstract] [Hide abstract] ABSTRACT: A review of methodology for separation, detection, and quantitative determination of catecholamines, 5-hydroxytryptamine, and their acidic metabolites in biological tissue and fluids by thin-layer chromatography is presented. Selected procedures, including fluorometric scanning densitometry for catecholamine acetyl derivatives and color scanning densitometry for acids, are described.
    No preview · Article · Jan 1999 · Journal of AOAC International
  • G Alemany · M Akaârir · C Rosselló · A Gamundi
    [Show abstract] [Hide abstract] ABSTRACT: A TLC method for the quantitative determination of epinephrine, norepinephrine and dopamine in rat plasma is described. After deprotenization, catecholamines were adsorbed on acid-alumina and acetylated. The acetyl derivatives were extracted using a C18 minicolumn, resolved on HPTLC plates and quantitated by fluorescence densitometry at 415 nm, using isoprenaline as internal standard.
    No preview · Article · Sep 1996 · Biomedical Chromatography
  • R Rial · A Gamundi · M Akaarir · C Rossello · JM Rayo · MC Nicolau
    No preview · Article · May 1996 · The Journal of Physiology