title: Evaluation of cortical local field potential diffusion in stereotactic electro-encephalography recordings: A glimpse on white matter signal.
abstract: While there is a strong interest in meso-scale field potential recording using intracranial electroencephalography with penetrating depth electrodes (i.e. stereotactic EEG or S-EEG) in humans, the signal recorded in the white matter remains ignored. White matter is generally considered electrically neutral and often included in the reference montage. Moreover, re-referencing electrophysiological data is a critical preprocessing choice that could drastically impact signal content and consequently the results of any given analysis. In the present stereotactic electroencephalography study, we first illustrate empirically the consequences of commonly used references (subdermal, white matter, global average, local montage) on inter-electrode signal correlation. Since most of these reference montages incorporate white matter signal, we next consider the difference between signals recorded in cortical gray matter and white matter. Our results reveal that electrode contacts located in the white matter record a mixture of activity, with part arising from the volume conduction (zero time delay) of activity from nearby gray matter. Furthermore, our analysis shows that white matter signal may be correlated with distant gray matter signal. While residual passive electrical spread from nearby matter may account for this relationship, our results suggest the possibility that this long distance correlation arises from the white matter fiber tracts themselves (i.e. activity from distant gray matter traveling along axonal fibers with time lag larger than zero); yet definitive conclusions about the origin of the white matter signal would require further experimental substantiation. By characterizing the properties of signals recorded in white matter and in gray matter, this study illustrates the importance of including anatomical prior knowledge when analyzing S-EEG data.
authors.affiliation: Department of Neurology, Montefiore Medical Center, 111 East 210th Street, Bronx, NY 10467, USA; Department of Neuroscience, Albert Einstein College of Medicine, 1410 Pelham Parkway South, Bronx, NY 10461, USA; Centre de Recherche Cerveau et Cognition (CerCo), CNRS, UMR5549, Pavillon Baudot CHU Purpan, BP 25202, 31052 Toulouse Cedex, France.
authors.forename: Manuel R
authors.initials: MR
authors.lastname: Mercier
authors.affiliation: Department of Neurology, Montefiore Medical Center, 111 East 210th Street, Bronx, NY 10467, USA.
authors.forename: Stephan
authors.initials: S
authors.lastname: Bickel
authors.affiliation: Department of Neurosurgery, Hofstra-Northwell School of Medicine and Feinstein Institute for Medical Research, Manhasset, New York, NY 11030, USA.
authors.forename: Pierre
authors.initials: P
authors.lastname: Megevand
authors.affiliation: Department of Neurosurgery, Hofstra-Northwell School of Medicine and Feinstein Institute for Medical Research, Manhasset, New York, NY 11030, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Groppe
authors.affiliation: Cognitive Neuroscience and Schizophrenia Program, Nathan Kline Institute, Orangeburg, NY 10962, USA; Department of Neurosurgery, Columbia College of Physicians and Surgeons, New York, NY 10032, USA.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Schroeder
authors.affiliation: Department of Neurosurgery, Hofstra-Northwell School of Medicine and Feinstein Institute for Medical Research, Manhasset, New York, NY 11030, USA.
authors.forename: Ashesh D
authors.initials: AD
authors.lastname: Mehta
authors.affiliation: Department of Neurology, Montefiore Medical Center, 111 East 210th Street, Bronx, NY 10467, USA; Department of Neuroscience, Albert Einstein College of Medicine, 1410 Pelham Parkway South, Bronx, NY 10461, USA. Electronic address: flado@montefiore.org.
authors.forename: Fred A
authors.initials: FA
authors.lastname: Lado
mesh_terms: D000328:Adult; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000379:methods*; D004827:Epilepsy / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery; D005260:Female; D066128:Gray Matter / Q000502:physiology*; D006801:Humans; D008297:Male; D013238:Stereotaxic Techniques; D066127:White Matter / Q000502:physiology*; D055815:Young Adult
keywords: Brain state; Epilepsy; Gray matter; Intracranial reference; Stereotactic electroencephalography; White matter