Advances of Electrophysiological Techniques in Pediatric Epilepsy

Recent advances in physics, engineering, signal, and image processing technologies have provided a unique opportunity to understand, diagnose, and assist with the treatment of severe neurological conditions, such as epilepsy. This special issue of the Journal of Pediatric Epilepsy reviews the innovative state-of-the art electrophysiological approaches applied in pediatric epilepsy. The following methods are discussed: magnetoencephalography (MEG) and magnetic source imaging (MSI), transcranial magnetic stimulation (TMS), simultaneous electroencephalography and functional magnetic resonance imaging (simultaneous EEG/fMRI), and real-time functional mapping (RTFM) together with other electrocorticography (ECoG)-based functional mapping modalities.

We begin with “Magnetoencephalography for clinical pediatrics: Recent advances in hardware, methods and clinical applications” article, where Gaetz et al provide a comprehensive overview of MEG as a completely non-invasive technique for studying the brain function. When combined with patient's MRI information, it results in MSI, an approach that allows detection of brain events with highly precise temporal and spatial resolution.[1] Importantly, this technique offers one-of-a-kind opportunity to visualize brain function from the first days of a child's development[2] and even in utero.[3]

The topic of identifying an irritative zone in epilepsy is thoroughly discussed in a distinctive contribution “High frequency oscillations in pediatric epilepsy: Methodology and clinical application.” Xiang et al provide their valuable expertise on the pioneering studies of high frequency oscillations (HFOs) and their applications to pediatric epilepsy and epilepsy in general. They discuss the most recent findings in invasive ECoG recordings, scalp EEG and MEG. The clinical importance of HFOs as markers of epileptogenicity and their application in different types of epilepsies are emphasized. From this review, it becomes evident that the utilization of HFOs in the identification of epileptogenic zone and presurgical evaluation[4] has strong potential to improve surgical outcomes.

Another field of electrophysiological approaches in epilepsy, TMS is reviewed in “Application of transcranial magnetic stimulation for diagnosis, treatment, and functional mapping in pediatric epilepsy.” Griskova-Bulanova focuses on three major areas of TMS application in pediatric epilepsy: (1) diagnostic measures of cortical excitability; (2) noninvasive presurgical functional mapping of epileptogenic zone and eloquent cortex; and (3) possible epilepsy treatment options through modulation of cortical excitability. This review supports current attempts to replace invasive technology used for presurgical epilepsy evaluation with noninvasive approaches.[5]

An innovative technology, combining electrophysiology and metabolic blood oxygenation-dependent imaging is presented in “Simultaneous EEG/fMRI and the identification of epileptic networks in children.” Malloy et al illustrate how the most recent advancements in data analysis approaches (e.g., Granger causality) combined with an EEG/fMRI methodology improve understanding of the mechanisms involved in the generation and propagation of ictal and interictal activity in epilepsy patients.[6] The unique property of simultaneous EEG/fRMI to provide high temporal resolution of EEG and exceptional spatial resolution of fMRI is highlighted.

The most recent developments in functional brain mapping technology applied to pediatric epilepsy are reviewed in “ECoG-based real-time functional mapping (RTFM) for pediatric epilepsy surgery.” Korostenskaja et al present a summary of ECoG-based functional mapping and developed by Schalk and Brunner RTFM techniques.[7] [8] The RTFM has a strong potential to become a valid alternative to the current gold standard of functional mapping—electrical cortical stimulation and reduce postsurgical morbidity.

Next is a data-driven review article “Contributions of magnetoencephalography to characterizing brain function in pediatric epilepsy: Evidences of validity and added value.” Castillo et al present data from 800 clinical cases that support the clinical validity of MEG procedure compared with the gold standards for the localization of both irritative zone and eloquent cortex.[9]

The special issue concludes with the review, where Stafstrom presents “Imaging anatomy of the human brain” book by Borden et al.[10] The review describes the major advantage of this book—utilization of images derived from various brain imaging techniques (such as fMRI, diffusion tensor imaging [DTI], positron emission tomography [PET], and others)—to help with understanding of human neuroanatomy. Stafstrom also offers suggestions about the use of this book by pediatric epileptologists.

As an invited editor of this special issue, I am very pleased that it received international contributions by invited authors from Japan, China, Austria, Lithuania, and different locations within the United States. I would like to express my gratitude to all of the contributing authors for their outstanding reviews. I hope that this special issue will help disseminate knowledge about the progress that has been made in the field of electrophysiology, advancing our understanding of pediatric epilepsy, its diagnosis, and lead to improved treatment outcomes.

• References

• 1 Wheless JW, Castillo E, Maggio V , et al. Magnetoencephalography (MEG) and magnetic source imaging (MSI). Neurologist 2004; 10 (3) 138-153
• 2 Okada Y, Pratt K, Atwood C , et al. BabySQUID: A mobile, high-resolution multichannel magnetoencephalography system for neonatal brain assessment. Rev Sci Instrum 2006; 77: 24301
• 3 Sheridan CJ, Matuz T, Draganova R, Eswaran H, Preissl H. Fetal Magnetoencephalography - Achievements and Challenges in the Study of Prenatal and Early Postnatal Brain Responses: A Review. Infant Child Dev 2010; 19 (1) 80-93
• 4 Leung H, Zhu CX, Chan DT , et al. Ictal high-frequency oscillations and hyperexcitability in refractory epilepsy. Clin Neurophysiol 2015;
• 5 Papanicolaou AC, Rezaie R, Narayana S , et al. Is it time to replace the Wada test and put awake craniotomy to sleep?. Epilepsia 2014; 55 (5) 629-632
• 6 Boor R, Jacobs J, Hinzmann A , et al. Combined spike-related functional MRI and multiple source analysis in the non-invasive spike localization of benign rolandic epilepsy. Clin Neurophysiol 2007; 118 (4) 901-909
• 7 Schalk G, Leuthardt EC, Brunner P, Ojemann JG, Gerhardt LA, Wolpaw JR. Real-time detection of event-related brain activity. Neuroimage 2008; 43 (2) 245-249
• 8 Brunner P, Ritaccio AL, Lynch TM , et al. A practical procedure for real-time functional mapping of eloquent cortex using electrocorticographic signals in humans. Epilepsy Behav 2009; 15 (3) 278-286
• 9 Papanicolaou AC, Pataraia E, Billingsley-Marshall R , et al. Toward the substitution of invasive electroencephalography in epilepsy surgery. J Clin Neurophysiol 2005; 22 (4) 231-237
• 10 Borden NM, Stefan C, Forseen SE. Imaging Anatomy of the Human Brain. New York, NY: Demos Medical; 2005