title: Spike avalanches in vivo suggest a driven, slightly subcritical brain state.
abstract: In self-organized critical (SOC) systems avalanche size distributions follow power-laws. Power-laws have also been observed for neural activity, and so it has been proposed that SOC underlies brain organization as well. Surprisingly, for spiking activity in vivo, evidence for SOC is still lacking. Therefore, we analyzed highly parallel spike recordings from awake rats and monkeys, anesthetized cats, and also local field potentials from humans. We compared these to spiking activity from two established critical models: the Bak-Tang-Wiesenfeld model, and a stochastic branching model. We found fundamental differences between the neural and the model activity. These differences could be overcome for both models through a combination of three modifications: (1) subsampling, (2) increasing the input to the model (this way eliminating the separation of time scales, which is fundamental to SOC and its avalanche definition), and (3) making the model slightly sub-critical. The match between the neural activity and the modified models held not only for the classical avalanche size distributions and estimated branching parameters, but also for two novel measures (mean avalanche size, and frequency of single spikes), and for the dependence of all these measures on the temporal bin size. Our results suggest that neural activity in vivo shows a mélange of avalanches, and not temporally separated ones, and that their global activity propagation can be approximated by the principle that one spike on average triggers a little less than one spike in the next step. This implies that neural activity does not reflect a SOC state but a slightly sub-critical regime without a separation of time scales. Potential advantages of this regime may be faster information processing, and a safety margin from super-criticality, which has been linked to epilepsy.
authors.affiliation: Department of Non-linear Dynamics, Max Planck Institute for Dynamics and Self-Organization Göttingen, Germany ; Bernstein Center for Computational Neuroscience Göttingen, Germany ; Frankfurt Institute for Advanced Studies Frankfurt, Germany ; Department of Neurophysiology, Max Planck Institute for Brain Research Frankfurt, Germany.
authors.forename: Viola
authors.initials: V
authors.lastname: Priesemann
authors.affiliation: Magnetoencephalography Unit, Brain Imaging Center, Johann Wolfgang Goethe University Frankfurt, Germany ; Ernst Strüngmann Institute for Neuroscience in Cooperation with Max Planck Society Frankfurt, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Wibral
authors.affiliation: Department of Biomedical Engineering, University of Los Andes Bogotá, Colombia.
authors.forename: Mario
authors.initials: M
authors.lastname: Valderrama
authors.affiliation: Neural Information Processing Group, Department of Software Engineering and Theoretical Computer Science, TU Berlin Berlin, Germany ; Bernstein Center for Computational Neuroscience Berlin, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Pröpper
authors.affiliation: Centre de Recherche de l'Institut du Cerveau et de la Moelle épinière, Hôpital de la Pitié-Salpêtrière, INSERM UMRS 975-CNRS UMR 7225-UPMC Paris, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Le Van Quyen
authors.affiliation: Department of Non-linear Dynamics, Max Planck Institute for Dynamics and Self-Organization Göttingen, Germany ; Bernstein Center for Computational Neuroscience Göttingen, Germany.
authors.forename: Theo
authors.initials: T
authors.lastname: Geisel
authors.affiliation: Frankfurt Institute for Advanced Studies Frankfurt, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Triesch
authors.affiliation: Frankfurt Institute for Advanced Studies Frankfurt, Germany ; Department of Neurophysiology, Max Planck Institute for Brain Research Frankfurt, Germany ; Ernst Strüngmann Institute for Neuroscience in Cooperation with Max Planck Society Frankfurt, Germany ; Department of Psychology, Faculty of Humanities and Social Sciences, University of Zagreb Zagreb, Croatia.
authors.forename: Danko
authors.initials: D
authors.lastname: Nikolić
authors.affiliation: Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics Tübingen, Germany.
authors.forename: Matthias H J
authors.initials: MH
authors.lastname: Munk
keywords: cortex; highly parallel recordings; human intracranial recordings; monkeys; multiunit activity; self-organized criticality; spike train analysis; spiking neural networks