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Objective: We recently proposed a spectrum-based model of the awake intracranial electroencephalogram (iEEG) (Kalamangalam et al., 2020), based on a publicly-available normative database (Frauscher et al., 2018). The latter has been expanded to include data from non-rapid eye movement (NREM) and rapid eye movement (REM) sleep (von Ellenrieder et al., 2020), and the present work extends our methods to those data., Methods: Normalized amplitude spectra on semi-logarithmic axes from all four arousal states (wake, N2, N3 and REM) were averaged region-wise and fitted to a multi-component Gaussian distribution. A reduced model comprising five key parameters per brain region was color-coded on to cortical surface models., Results: The lognormal Gaussian mixture model described the iEEG accurately from all brain regions, in all sleep-wake states. There was smooth variation in model parameters as sleep and wake states yielded to each other. Specific observations unrelated to the model were that the primary cortical areas of vision, motor function and audition, in addition to the hippocampus, did not participate in the 'awakening' of the cortex during REM sleep., Conclusions: Despite the significant differences in the appearance of the time-domain EEG in wakefulness and sleep, the iEEG in all arousal states was successfully described by a parametric spectral model of low dimension., Significance: Spectral variation in the iEEG is continuous in space (across different cortical regions) and time (stage of circadian cycle), arguing for a 'continuum' hypothesis in the generative processes of sleep and wakefulness in human brain., Competing Interests: Declaration of Competing Interest None., (Copyright © 2021 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)

Analysis of scalp electroencephalogram (EEG) findings is indispensable to investigation of epilepsy surgery candidates. Maxima of slowing and epileptiform spiking on interictal EEG reflect gross localization of core epileptogenic regions within a network. Important negative scalp EEG findings are those associated with deep foci. Ictal EEG is important in confirming concordance with interictal EEG and other ancillary data. Generalized interictal and ictal EEG findings may occur in epilepsies that are otherwise focal. Detailed individual analyses of scalp EEG features are prelude to a more global synthesis, whose coherence in suggesting plausible network hypothesis presage a subsequently successful scalp EEG evaluation., Competing Interests: Disclosure The author has nothing to disclose., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Objective: A library of intracranial electroencephalography (iEEG) from the normal human brain has recently been made publicly available (Frauscher et al., 2018). The library - which we term the Montreal Neurological Institute Atlas (MNIA) - comprises 30 hours of iEEG from over a hundred epilepsy patients. We present a Fourier spectrum-based model of low dimension that summarizes all of MNIA into a neurophysiological 'brain map'., Methods: Normalized amplitude spectra of the MNIA data were modelled as log-normal distributions around individual canonical Berger frequencies. The latter were concatenated to yield the composite spectrum with high accuracy. Key model parameters were color-coded into a visual representation on cortical surface models., Results: Each brain region has its own spectral characteristics that together yield a novel composite intracranial EEG brain map., Conclusions: iEEG from normal brain regions can be accurately modelled with a small number of independent parameters. Our model is based in the canonical Berger bands and naturally suits clinical electroencephalography., Significance: Due to its applicability to iEEG from all sampled regions, the model suggests a certain universality to brain rhythm generation that is independent of precise cortical location. More generally, our results are a novel abstraction of resting cortical dynamics that may help diagnostics in epileptology, in addition to informing structure-function relationships in the field of human brain mapping., Competing Interests: Declaration of Competing Interests None., (Copyright © 2019 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)

Identifying the localization, distribution, and polarity of waveforms are the prime goals of clinical scalp EEG analysis. Appropriate choices of bipolar and referential montages are keys to emphasizing the diagnostic features of interest, and demand some understanding of the spatiotemporal physical behavior of the underlying neuronal generators. Several examples drawn from canonical epilepsy syndromes are used to illustrate this general message.

The term "ictal-interictal" continuum has seen wide adoption in the critical care EEG domain, referring to the presence of abnormal periodic activity on the scalp EEG variably associated with seizures. The historical origin of the ictal-interictal continuum concept is discussed with a review of known and surmised physiological mechanisms for their origin and relationship to seizures. Therapeutic approaches to patients exhibiting ictal-interictal continuum EEG patterns are reviewed, and some open scientific questions highlighted. Further understanding of the ictal-interictal continuum is likely to significantly improve the care of the critically ill neurological patient.

Objective: Visually-obvious abnormalities in the resting baseline EEG--slowing, spiking and high-frequency oscillations (HFOs)--are cardinal, though incompletely understood, features of the seizure onset zone in focal epilepsy. We hypothesized that evidence of cortical network dysfunction in temporal lobe epilepsy (TLE) would persist in the absence of visually-classifiable abnormalities in the baseline EEG recorded within the conventional passband, and that metrics of such dysfunction could serve as a lateralizing diagnostic in TLE., Methods: Epochs of resting EEG without significant abnormalities in light sleep over several days were compared between a group of 10 patients with proven TLE and 10 subjects without epilepsy. A novel laterality metric computed from the line length of normalized power spectra from the temporal channels was compared between the two groups., Results: Significant group differences in spectral line length laterality metric were found between the TLE and control group. At the individual level, seven of 10 TLE patients had highly significant laterality metrics, all concordant with the known laterality of their disease., Significance: Detailed spectral analysis offers novel insight into TLE network behavior, independent of the orthodox abnormalities of EEG slowing, spikes or HFOs. The results may be deployed in a practical diagnostic manner, offer insight into the EEG manifestations of disordered cellular network architecture in TLE, and maybe understood through simple analogy with the theory of linear time-invariant physical systems., (Copyright © 2014 Elsevier B.V. All rights reserved.)

We explored the diagnostic value of oxygen-enhanced MRI, a novel technique for measuring regional brain metabolism, in a set of normal adult volunteers and temporal lobe epilepsy patients. Eight right-handed adult normal volunteers and ten right-handed patients with temporal lobe epilepsy were studied. Six patients had lesions concordant with their epilepsy on high-resolution (3T) structural MRI. Four patients were nonlesional. Hyperoxia (oxygen enhancement, OE) was carried out by administering 100% O(2) in epochs by mask or cannula interleaved with breathing of normal atmospheric air. The T2* (blood oxygen level dependent, BOLD) signal was recorded in continuously acquired echo-planar images. Data from nine temporal lobe subregions were subjected to spectral analysis and statistical testing. OE resulted in unambiguous concordant positive T2* signal change in all subjects. Analysis of the distribution of spectral power within the temporal lobe revealed a significant (p<0.025, one-sided) group difference between normals and epilepsy patients, with seven patients exhibiting large deviations from normalcy that lateralized their disease. Two such patients had nonlesional MRIs. Oxygen-enhanced MRI is a promising metabolic imaging modality for the diagnosis and lateralization of oxidative metabolic derangement associated with lesional and nonlesional temporal lobe epilepsy., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Purpose: The early phase of motor seizures in focal epilepsy produces asymmetry of scalp electromyogram (ASEMG), observable as right-left inequality in muscle artifact on EEG. ASEMG is concordant with clinical lateralization when the seizure has clearly unilateral motor features (tonic, clonic, or versive movements), with higher electromyogram contralateral to the hemisphere of seizure onset. The authors explored whether ASEMG was also present in motor seizures without visible lateralizing signs., Methods: Seizure classification by video telemetry data in a group of 106 focal epilepsy patients by semiology and ictal EEG. Assessment of ASEMG laterality by two reviewers. Computation of the κ index of interobserver reliability. Calculation of the sensitivity and positive predictive value of ASEMG in motor seizures with regard to the laterality of the epileptogenic zone., Results: Forty-eight of 106 patients had at least 1 motor seizure recorded. Of the total of 257 seizures recorded in the former, 174 (≈68%) had a motor component. Forty such seizures had no clinical or EEG lateralization; ASEMG was, however, identified and accurate in 39 (97.5%). Generally, ASEMG was identified in 158 (90.8%) of all motor seizures, correctly lateralizing 156 (89.6%). The next most common lateralizing sign was unilateral tonic, clonic, or dystonic posturing (44.8%)., Conclusions: ASEMG is an accurate lateralizing sign, useful in seizures that have no alternative clinical lateralizing signs or ictal EEG lateralization. ASEMG was present in >90% of all motor seizures in this series, with a positive predictive value of 156 (>98%) of 158.

Purpose: To investigate reasons for patients not proceeding to resective epilepsy surgery after subdural grid evaluation (SDE). To correlate noninvasive investigation results with invasive EEG observations in a set of patients with nonlesional brain MRIs., Methods: Retrospective study of adult epilepsy patients undergoing SDE during an 8-year period at Cleveland Clinic. Construction of semiquantitative "scores" and Bayesian predictors summarizing the localizing value and concordance between noninvasive parameters in a subset with nonlesional MRIs., Results: One hundred forty patients underwent SDE, 25 of whom were subsequently denied resective surgery. In 10 of 25, this was caused by a nonlocalizing subdural ictal EEG onset. Eight of 10 such patients were nonlesional on MRI. Among all nonlesional patients (n = 34 of 140), n1 = 10 of 34 patients had nonlocalizing and n2 = 24 of 34 had localizing, subdural ictal onsets. As groups, n1 and n2 were statistically disjoint relative to their noninvasive scores. Bayesian measures predictive of focal invasive ictal EEG were highest for complete concordance of noninvasive parameters, decreasing with lesser degrees of concordance. A localizing scalp interictal EEG was a particularly good Bayesian prognosticator., Conclusions: A small but significant proportion of SDE patients are denied subsequent therapeutic resective surgery. This is due to several reasons, including a nonlocalizing intracranial ictal EEG. The majority of such patients have nonlesional MRIs. The noninvasive data may be summarized by a semiquantitative score, as well as Bayesian likelihood ratios, which correlate with subsequent invasive outcome. This approach may find use in the selection and counseling of potential surgical candidates offered SDE.

Purpose: We assessed neuroimaging lesion type and distribution in patients with periodic lateralized epileptiform discharges (PLEDs), with a view to identifying electrographic differences between PLEDs associated with differing lesion locations. Our observations led us to consider a conceptual synthesis between PLEDs and periodic complexes (PCs)., Methods: Retrospective review of acute neuroimaging results (CT/MRI) on patients identified to have EEG PLEDs, for the period 1999-2003 (n=106). Blinded classification of original EEG recordings., Results: Neuroimaging abnormalities were classified as acute or chronic cortical, or acute or chronic subcortical. Seven out of 106 scans were classified nonlesional. Overall approximately 70% of scans had cortical abnormalities, whether acute or chronic; approximately 23% had subcortical abnormalities. "Cortical" PLEDs were significantly longer in duration (p<0.05) and more variable in morphology (p<0.01) than "subcortical" PLEDs., Conclusions: Structural brain disease commonly, but not invariably, underlies PLEDs; lesion type is spatiotemporally variable. Cortical and subcortical PLEDs have distinct EEG signatures. There is evidence that these may relate to mechanisms for other pathological large-scale oscillatory brain synchronies (e.g., PCs).

The issue of human consciousness, in both its popular and neuroscientific sense, is considered from a clinical perspective. The ictal semiologies of the various epilepsies, together with associated clinical features, are demonstrated to highlight certain neuroanatomical and neurophysiological facets of consciousness. It is suggested that further insights into consciousness, even those bordering on the philosophical, may be led by clinical neurological phenomena and emerging neuroinvestigative techniques., (Copyright 2001 BEA Trading Ltd.)