Rogue bioelectrical waves in the brain: the Hurst exponent as a potential measure for presurgical mapping in epilepsy

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Abstract

OBJECTIVE: Brain electromagnetic activity in patients with epilepsy is characterized by abnormal high-amplitude transient events (spikes) and abnormal patterns of synchronization of brain rhythms that accompany epileptic seizures. With the aim of improving methods for identifying epileptogenic sources in magnetoencephalographic (MEG) recordings of brain data, we applied methods previously used in the study of oceanic 'rogue waves' and other freak events in complex systems 
 Approach. For data from 3 patients who were awaiting surgical treatment for epilepsy, we used a beamformer source-model to produce volumetric maps showing areas with a high proportion of spikes that could be classified as 'rogue waves', and areas with high Hurst Exponent (HE). The HE describes the extent to which a system is exhibiting persistent behavior, may predict the likelihood of freak events. These measures were compared with the more standard measure of kurtosis, known to be a reliable method for localizing interictal spikes.
 Main Results. There was partial concordance between the 3 different volumetric maps indicating that each measure provides different information about the underlying brain data. The HE, when combined with a simple connectivity analysis based on phase slope index, could identify the probable epileptogenic zone in all 3 patients, despite very different patterns of abnormal activity. The differences between distributions of high HE and high kurtosis values indicate that while spikes are propagated through cortex from the epileptogenic zone, the persistent dynamical conditions under which the spikes are generated may not be propagated in a similar way. Finally, patterns of persistent activity, indicating a departure from 'healthy criticality' in brain networks may explain the wide range of social and cognitive impairments that are seen in epilepsy patients. 
 Significance. The HE is a potentially useful addition to the clinician's battery of measures which may be used convergently to guide surgical intervention.
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  • bioelectrical waves in the brain

    Rights statement: © 2018 IOP Publishing Ltd. As the Version of Record of this article is going to be/has been published on a subscription basis, this Accepted Manuscript will be available for reuse under a CC BY-NC-ND 3.0 licence after a 12 month embargo period.

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Original languageEnglish
JournalJournal of Neural Engineering
Early online date17 May 2019
DOIs
Publication statusE-pub ahead of print - 17 May 2019

Bibliographic note

© 2018 IOP Publishing Ltd. As the Version of Record of this article is going to be/has been published on a subscription basis, this Accepted Manuscript will be available for reuse under a CC BY-NC-ND 3.0 licence after a 12 month embargo period. After the embargo period, everyone is permitted to use copy and redistribute this article for non-commercial purposes only, provided that they adhere to all the terms of the licence https://creativecommons.org/licences/by-nc-nd/3.0. Funding: Dr Hadwen Trust for Humane Research, Leverhulme Trust (Grant ref: RPG-2014-304), H2020-MSCA-RISE-20165 project CARDIALLY.

    Keywords

  • magetoencephalography, epilepsy, Hurst, Nonlinear dynamics

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