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J Neurosci. 2014 May 7;34(19):6557-72. doi: 10.1523/JNEUROSCI.4701-13.2014.

Scale-free bursting in human cortex following hypoxia at birth.

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  • 1Systems Neuroscience Group, QIMR Berghofer Medical Research Institute, Brisbane, Queensland 4006, Australia, Faculty of Health Sciences, School of Medicine, University of Queensland, Brisbane, Queensland 4029, Australia, The University of Queensland Centre for Clinical Research and Perinatal Research Centre, Brisbane, Queensland 4006, Australia, Department of Children's Clinical Neurophysiology, Helsinki University Central Hospital and University of Helsinki, Helsinki HUS 00029, Finland, Royal Brisbane and Women's Hospital, Herston, Queensland 4006, Australia, and School of Psychiatry, University of New South Wales and The Black Dog Institute, Randwick, New South Wales 2031, Australia.


The human brain is fragile in the face of oxygen deprivation. Even a brief interruption of metabolic supply at birth challenges an otherwise healthy neonatal cortex, leading to a cascade of homeostatic responses. During recovery from hypoxia, cortical activity exhibits a period of highly irregular electrical fluctuations known as burst suppression. Here we show that these bursts have fractal properties, with power-law scaling of burst sizes across a remarkable 5 orders of magnitude and a scale-free relationship between burst sizes and durations. Although burst waveforms vary greatly, their average shape converges to a simple form that is asymmetric at long time scales. Using a simple computational model, we argue that this asymmetry reflects activity-dependent changes in the excitatory-inhibitory balance of cortical neurons. Bursts become more symmetric following the resumption of normal activity, with a corresponding reorganization of burst scaling relationships. These findings place burst suppression in the broad class of scale-free physical processes termed crackling noise and suggest that the resumption of healthy activity reflects a fundamental reorganization in the relationship between neuronal activity and its underlying metabolic constraints.


EEG; burst suppression; hypoxia; neonates; neuronal avalanches; scale-free

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