title: Self-organized dynamical complexity in human wakefulness and sleep: different critical brain-activity feedback for conscious and unconscious states.
abstract: Criticality reportedly describes brain dynamics. The main critical feature is the presence of scale-free neural avalanches, whose auto-organization is determined by a critical branching ratio of neural-excitation spreading. Other features, directly associated to second-order phase transitions, are: (i) scale-free-network topology of functional connectivity, stemming from suprathreshold pairwise correlations, superimposable, in waking brain activity, with that of ferromagnets at Curie temperature; (ii) temporal long-range memory associated to renewal intermittency driven by abrupt fluctuations in the order parameters, detectable in human brain via spatially distributed phase or amplitude changes in EEG activity. Herein we study intermittent events, extracted from 29 night EEG recordings, including presleep wakefulness and all phases of sleep, where different levels of mentation and consciousness are present. We show that while critical avalanching is unchanged, at least qualitatively, intermittency and functional connectivity, present during conscious phases (wakefulness and REM sleep), break down during both shallow and deep non-REM sleep. We provide a theory for fragmentation-induced intermittency breakdown and suggest that the main difference between conscious and unconscious states resides in the backwards causation, namely on the constraints that the emerging properties at large scale induce to the lower scales. In particular, while in conscious states this backwards causation induces a critical slowing down, preserving spatiotemporal correlations, in dreamless sleep we see a self-organized maintenance of moduli working in parallel. Critical avalanches are still present, and establish transient auto-organization, whose enhanced fluctuations are able to trigger sleep-protecting mechanisms that reinstate parallel activity. The plausible role of critical avalanches in dreamless sleep is to provide a rapid recovery of consciousness, if stimuli are highly arousing.
authors.affiliation: Istituto di Scienze della Vita, Scuola Superiore Sant'Anna, Piazza Martiri della Libertà 7, 56127 Pisa, Italy.|Istituto di Fisiologia Clinica (IFC-CNR), Via Moruzzi 1, 56124 Pisa, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Allegrini
authors.affiliation: Istituto di Scienza e Tecnologie dell'Informazione "A. Faedo" (ISTI-CNR), Via Moruzzi 1, 56124 Pisa, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Paradisi
authors.affiliation: Istituto di Fisiologia Clinica (IFC-CNR), Via Moruzzi 1, 56124 Pisa, Italy.|Dipartimento di Ricerca Traslazionale e delle Nuove Tecnologie in Medicina e Chirurgia, Via Savi 10, 56126 Pisa, Italy.
authors.forename: Danilo
authors.initials: D
authors.lastname: Menicucci
authors.affiliation: Istituto di Scienze della Vita, Scuola Superiore Sant'Anna, Piazza Martiri della Libertà 7, 56127 Pisa, Italy.|Istituto di Fisiologia Clinica (IFC-CNR), Via Moruzzi 1, 56124 Pisa, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Laurino
authors.affiliation: PERCRO laboratory, Scuola Superiore Sant'Anna, Piazza Martiri della Libertà 7, 56127 Pisa, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Piarulli
authors.affiliation: Istituto di Scienze della Vita, Scuola Superiore Sant'Anna, Piazza Martiri della Libertà 7, 56127 Pisa, Italy.|Istituto di Fisiologia Clinica (IFC-CNR), Via Moruzzi 1, 56124 Pisa, Italy.|Dipartimento di Patologia Chirurgica, Medica, Molecolare e dell'Area Critica, Università di Pisa, Via Savi 10, 56126 Pisa, Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: Gemignani
mesh_terms: D001921:Brain / Q000502:physiology*; D003243:Consciousness / Q000502:physiology*; D004569:Electroencephalography; D025461:Feedback, Physiological / Q000502:physiology*; D006801:Humans; D009434:Neural Pathways / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D012890:Sleep / Q000502:physiology*; D014474:Unconsciousness / Q000503:physiopathology*; D014851:Wakefulness / Q000502:physiology*