Spikes and Epilepsy

Abstract

Digital EEG analysis provides significantly more information to the clinical electroencephalographer (EEGer) for scalp as well as for intracranial monitoring than is currently being routinely utilized. When modern data analysis software is used, interictal spikes contain considerably more information than had previously been ascribed to them. To optimize the diagnostic value of the EEG, sleep recordings after sleep deprivation is valuable because focal spikes, unless abundant, are relatively rare in the waking state. Recording time should also be sufficiently long to allow spikes to emerge. Spikes are always pathologic and can be associated with impaired cerebral perfusion, metabolic changes and concomitant behavioral changes. They can also be separated into simple and complex forms which may allow prognostic statements. The simplest way to accomplish this is by placing a cursor on the peak of the spike and see whether or not other channels show latency differences. More precise methods are: comparisons of voltage maps with current source density maps, principal component analysis and distinctions between stationary versus moving dipoles. Averaging of spikes is valuable but care must be taken that only those spikes which have the same distribution are averaged, and when the average is obtained only from the spike peak, propagation may already have occurred. It has been recommended that the midpoint of the ascending negative phase be used as the point for averaging. In intracranial recordings the frequencies above the gamma range should also be assessed. Their small electrical field allows a differentiation between locally generated events from those which are volume conducted and can thereby more accurately reflect the epileptogenic zone(s). High frequency activity can also be recorded from foramen ovale electrodes which enhances their diagnostic utility. It is emphasized that for centers which perform pre-surgical evaluations the software supplied by instrument manufacturers is inadequate and needs to be supplemented by additional commercially available programs. Furthermore, archived data should be used for retrospective investigations and follow-up studies of patients who have undergone either excisions, resections, or multiple subpial transections to evaluate the success rates by taking into account all the properties of interictal and ictal recordings which are mentioned in this article.

Aberrant Cortical Activity In Multiple GCaMP6-Expressing Transgenic Mouse Lines

“…In epileptic patients and animal models, interictal spikes are a commonly observed phenomenon. These large, brief electrical events are observable in EEG, ECoG, and intracranial recordings, and are considered to always be pathological (Rodin et al, 2009). Whether they merely represent a symptom of a damaged brain, actively induce future seizures, or even act preventatively remains disputed (Staley et al, 2011).…”

Epileptic Neuronal Networks: Methods of Identification and Clinical Relevance

“…Indeed inter-ictal EEG (reviewed in Rodin et al, 2009) and MEG spikes (Tanaka et al, 2010) may be considered biomarkers of epileptogenic networks; more recently, in the same context, a novel kind of biomarker – High Frequency Oscillations, i.e., HFOs (ripples and fast ripples), – has raised a lot of interest and its role is the object of investigation, reviewed by Jacobs et al (2012). In order to perform this kind of analyses using scalp EEG and/or MEG recordings it is necessary to combine information about electric and/or magnetic fields with anatomical information obtained from MRI.…”

Layer‐ and Cell‐Specific Recruitment Dynamics during Epileptic Seizures In Vivo

“…The difference between layer 2/3 PNs and PV‐expressing INs is also manifested in the relative increase of the peak calcium response and Pearson correlation coefficient between the onset of spikes and seizures. In layer 2/3 PNs, the averaged peak calcium responses during onset of seizures was 145 ± 31% larger than during onset of spikes (50 spikes and 40 seizures, 7 mice, SEM estimated by bootstrap with 10 resamples), compared to only 14 ± 12% in PV‐expressing INs (50 spikes and 32 seizures, 5 mice). Importantly, the difference between the dynamics of layer 2/3 PNs and PV‐expressing INs was not caused by saturation of the fluorescent signals or buffering of the intracellular calcium concentrations, as in all cases of both layer 2/3 PNs and PV‐expressing INs the fluorescent signals reached higher values as seizures evolved.…”

“…Although crucial for predicting seizures and developing new therapies, the process of interictal to ictal state transition is not well understood. In addition to seizures, epileptic cortical networks also generate brief abnormal discharges, termed spikes and sharp waves, which are unaccompanied by any noticeable clinical features . The relationship between brief interictal spikes and seizures is unclear .…”