Characterization of network structure in stereoEEG data using consensus-based partial coherence.

Coherence is a widely used measure to determine the frequency-resolved functional connectivity between pairs of recording sites, but this measure is confounded by shared inputs to the pair. To remove shared inputs, the 'partial coherence' can be computed by conditioning the spectral matrices of the pair on all other recorded channels, which involves the calculation of a matrix (pseudo-) inverse. It has so far remained a challenge to use the time-resolved partial coherence to analyze intracranial recordings with a large number of recording sites. For instance, calculating the partial coherence using a pseudoinverse method produces a high number of false positives when it is applied to a large number of channels. To address this challenge, we developed a new method that randomly aggregated channels into a smaller number of effective channels on which the calculation of partial coherence was based. We obtained a 'consensus' partial coherence (cPCOH) by repeating this approach for several random aggregations of channels (permutations) and only accepting those activations in time and frequency with a high enough consensus. Using model data we show that the cPCOH method effectively filters out the effect of shared inputs and performs substantially better than the pseudo-inverse. We successfully applied the cPCOH procedure to human stereotactic EEG data and demonstrated three key advantages of this method relative to alternative procedures. First, it reduces the number of false positives relative to the pseudo-inverse method. Second, it allows for titration of the amount of false positives relative to the false negatives by adjusting the consensus threshold, thus allowing the data-analyst to prioritize one over the other to meet specific analysis demands. Third, it substantially reduced the number of identified interactions compared to coherence, providing a sparser network of connections from which clear spatial patterns emerged. These patterns can serve as a starting point of further analyses that provide insight into network dynamics during cognitive processes. These advantages likely generalize to other modalities in which shared inputs introduce confounds, such as electroencephalography (EEG) and magneto-encephalography (MEG).

Long-duration epilepsy affects cell morphology and glutamatergic synapses in type IIB focal cortical dysplasia.

To investigate hypothesized effects of severe epilepsy on malformed cortex, we analyzed surgical samples from eight patients with type IIB focal cortical dysplasia (FCD) in comparison with samples from nine non-dysplastic controls. We investigated, using stereological quantification methods, where appropriate, dysplastic neurons, neuronal density, balloon cells, glia, glutamatergic synaptic input, and the expression of N-methyl-D-aspartate (NMDA) receptor subunits and associated membrane-associated guanylate kinase (MAGUK). In all FCD patients, the dysplastic areas giving rise to epileptic discharges were characterized by larger dysmorphic neurons, reduced neuronal density, and increased glutamatergic inputs, compared to adjacent areas with normal cytology. The duration of epilepsy was found to correlate directly (a) with dysmorphic neuron size, (b) reduced neuronal cell density, and (c) extent of reactive gliosis in epileptogenic/dysplastic areas. Consistent with increased glutamatergic input, western blot revealed that NMDA regulatory subunits and related MAGUK proteins were up-regulated in epileptogenic/dysplastic areas of all FCD patients examined. Taken together, these results support the hypothesis that epilepsy itself alters morphology-and probably also function-in the malformed epileptic brain. They also suggest that glutamate/NMDA/MAGUK dysregulation might be the intracellular trigger that modifies brain morphology and induces cell death.

Epilepsy surgery in children: evaluation of seizure outcome and predictive elements.

PURPOSE: To analyze the clinical outcome of epilepsy surgery in children, and to identify the factors related with a favorable seizure control among several presurgical, surgical and postsurgical variables. METHODS: One-hundred twenty children, younger than 16 years (69 male and 51 female), operated on for medically refractory focal epilepsy at the "C.Munari" Epilepsy Surgery Center of the Niguarda Hospital in Milan from 1998 to 2009, were identified. Seizure outcome was assessed according to the Engel's classification. Statistical analysis was performed to identify predictive elements of seizure outcome among several presurgical, surgical, and postsurgical variables. KEY FINDINGS: There were 84 (70%) seizure-free patients (Engel's classes Ia and Ic), 93 (77.5%) in class I, 8 (6.7%) in class II, 9 in class III (7.5%), and 10 (8.3%) in class IV. SIGNIFICANCE: Our study confirms that epilepsy surgery is an established and effective treatment for partial epilepsy in children and suggest criteria to help identify early potential surgical candidates.

Health Technology Assessment report on the presurgical evaluation and surgical treatment of drug-resistant epilepsy.

PURPOSE: Epilepsy is a neurologic disorder with major social impact. Surgery is a valuable option in patients who are not responding to antiepileptic drugs. The literature reports demonstrate that a proportion ranging from 40 to 100% of patients with epilepsy achieve seizure remission after surgery. A presurgical evaluation (clinical and instrumental) must be performed in all patients with drug-resistant epilepsy to assess their suitability for surgical intervention. Health Technology Assessment (HTA) represents a modern approach to the analysis of technologies used for health care. HTA could be considered a bridge between science that produces evidence and the decisions that can be taken on the basis of that evidence at different levels of the health care system. The aim of this study is the HTA of epilepsy surgery including clinical, ethical, social, and economic features. METHODS: The present study includes an analysis of the diagnostic and surgical workup performed at the Italian centers for the diagnosis and treatment of drug-resistant epilepsy (DRE). The study includes the following issues: (1) social, ethical impact, and costs of the disease; (2) clinical results, efficacy, and safety of surgery; (3) ethics and quality of life after surgery; and (4) economic impact and productivity regained after surgery. The cost of managing a patient with DRE included in the presurgical study was estimated by the bottom-up microcosting technique that starts from a detailed collection of data on consumption of resources and full costing. The phases analyzed were (1) noninvasive diagnostic workup; (2) neurosurgical intervention; and (3) follow-up. KEY FINDINGS: The literature reports indicate epilepsy surgery as an effective treatment both on clinical results and on ethical, social, and quality of life aspects. The workup including the noninvasive presurgical study followed by surgery has a total cost of €20,827. Management of short-term follow-up increases the overhead to €22,291 at the first year, and then to €23,571 after 5 years. According to the estimates made in this survey, funding based on diagnosis-related group (DRG) tariff for the noninvasive diagnostic stage involving hospital admission is not remunerative in Italy either at regional or national levels. Effectively the difference between full cost and DRG has a delta of €3,402 and €2,537 respectively. The total cost of the presurgical, surgical, and follow-up evaluation is not remunerative for €10,554 (national data). SIGNIFICANCE: Economic surveys in Italy have shown that surgery for DRE is an advantageous treatment from the standpoint of third-party payers and is cost-effective for society. DRE presurgical evaluation and surgery are not remunerative either at regional or national levels.

Dissociated local arousal states underlying essential clinical features of non-rapid eye movement arousal parasomnia: an intracerebral stereo-electroencephalographic study.

Sleep has been shown to be a global phenomenon in which the presence of local processes of both activation and deactivation are finely orchestrated. Dysfunctional and independent action of the systems involved in non-rapid eye movement (NREM) sleep and wakefulness is deemed to be at the basis of arousal parasomnias. We show, in a patient with confusional arousals, persistence of sleep in the hippocampal and frontal associative cortices in contrast to the presence of awakening in the motor, cingulate, insular, amygdalar and temporopolar cortices. The clinical features of the confusional arousals in this patient are highly consistent with a dysfunctional coexistence of local cortical arousal and local cortical sleep.

Human stereoEEG recordings reveal network dynamics of decision-making in a rule-switching task.

The processing steps that lead up to a decision, i.e., the transformation of sensory evidence into motor output, are not fully understood. Here, we combine stereoEEG recordings from the human cortex, with single-lead and time-resolved decoding, using a wide range of temporal frequencies, to characterize decision processing during a rule-switching task. Our data reveal the contribution of rostral inferior parietal lobule (IPL) regions, in particular PFt, and the parietal opercular regions in decision processing and demonstrate that the network representing the decision is common to both task rules. We reconstruct the sequence in which regions engage in decision processing on single trials, thereby providing a detailed picture of the network dynamics involved in decision-making. The reconstructed timeline suggests that the supramarginal gyrus in IPL links decision regions in prefrontal cortex with premotor regions, where the motor plan for the response is elaborated.

Could the 2017 ILAE and the four-dimensional epilepsy classifications be merged to a new "Integrated Epilepsy Classification"?

Over the last few decades the ILAE classifications for seizures and epilepsies (ILAE-EC) have been updated repeatedly to reflect the substantial progress that has been made in diagnosis and understanding of the etiology of epilepsies and seizures and to correct some of the shortcomings of the terminology used by the original taxonomy from the 1980s. However, these proposals have not been universally accepted or used in routine clinical practice. During the same period, a separate classification known as the "Four-dimensional epilepsy classification" (4D-EC) was developed which includes a seizure classification based exclusively on ictal symptomatology, which has been tested and adapted over the years. The extensive arguments for and against these two classification systems made in the past have mainly focused on the shortcomings of each system, presuming that they are incompatible. As a further more detailed discussion of the differences seemed relatively unproductive, we here review and assess the concordance between these two approaches that has evolved over time, to consider whether a classification incorporating the best aspects of the two approaches is feasible. To facilitate further discussion in this direction we outline a concrete proposal showing how such a compromise could be accomplished, the "Integrated Epilepsy Classification". This consists of five categories derived to different degrees from both of the classification systems: 1) a "Headline" summarizing localization and etiology for the less specialized users, 2) "Seizure type(s)", 3) "Epilepsy type" (focal, generalized or unknown allowing to add the epilepsy syndrome if available), 4) "Etiology", and 5) "Comorbidities & patient preferences".

Evidence of dissociated arousal states during NREM parasomnia from an intracerebral neurophysiological study.

STUDY OBJECTIVES: Arousal parasomnias are expressions of sleep/ wake state dissociations in which wakefulness and NREM sleep seem to coexist. We describe the results of a neurophysiological (intracerebral EEG) investigation that captured an episode of confusional arousal. DESIGN: Observational analysis. SETTING: Tertiary sleep center. SUBJECT: A 20-year-old male with refractory focal epilepsy. MEASUREMENTS AND RESULTS: The intracerebral EEG findings documented the presence of a local arousal of the motor and cingulate cortices associated with increased delta activity in the frontoparietal associative cortices; these findings were noted preceding the onset and persisting throughout the episode. CONCLUSIONS: The presence of dissociated sleep/wake states in confusional arousals is the expression not of a global phenomenon, but rather of the coexistence of different local states of being: arousal of the motor and cingulate cortices and inhibition of the associative ones. Whether this is an exclusive feature of NREM parasomnias, or a common substrate on which other triggering elements act, needs to be clarified.

Rapid and specific processing of person-related information in human anterior temporal lobe.

The anterior temporal lobe (ATL), located at the tip of the human temporal lobes, has been heavily implicated in semantic processing by neuropsychological and functional imaging studies. These techniques have revealed a hemispheric specialization of ATL, but little about the time scale on which it operates. Here we show that ATL is specifically activated in intracerebral recordings when subjects discriminate the gender of an actor presented in a static frame followed by a video. ATL recording sites respond briefly (100 ms duration) to the visual static presentation of an actor in a task-, but not in a stimulus-duration-dependent way. Their response latencies correlate with subjects' reaction times, as do their activity levels, but oppositely in the two hemispheres operating in a push-pull fashion. Comparison of ATL time courses with those of more posterior, less specific regions emphasizes the role of inhibitory operations sculpting the fast ATL responses underlying semantic processing.

NMDA receptor composition differs among anatomically diverse malformations of cortical development.

Altered excitatory synaptic activity is likely a key factor in the neuronal hyperexcitability of developmental cerebral malformations. Using a combined morphologic and molecular approach, we investigated the NMDA receptor and related protein composition in human epileptic patients affected by periventricular nodular heterotopia, subcortical band heterotopia, or focal cortical dysplasia. Our results indicate that expression levels of specific NMDA receptor subunits are altered in both cerebral heterotopia and cortical dysplasia. A selective increase in the NR2B subunit was present in all cortical dysplasia, whereas the expression level of NR2A and NR2B subunits was significantly downregulated in all patients with heterotopia. NR2B upregulation in cortical dysplasia was greater in the total homogenate than the postsynaptic membrane fraction, suggesting that mechanisms other than increased ionic influx through the postsynaptic membrane may sustain hyperexcitability in dysplastic neurons. In cerebral heterotopia, the NR2A and NR2B downregulation was accompanied by less evident reduction of the SAP97 and PSD-95 proteins of the MAGUK family, thus suggesting that NMDA impairment was associated with altered molecular structure of the postsynaptic membrane. Our results demonstrate that diverse human developmental malformations are associated with different alterations of the NMDA receptor, which may contribute to the genesis of epileptic phenomena.

Coupling of minor motor events and epileptiform discharges with arousal fluctuations in NFLE.

PURPOSE: We recently demonstrated that in nocturnal frontal lobe epilepsy (NFLE) highly stereotyped minor motor events (MMEs, in the form of short-lasting stereotyped movements involving the limbs, the axial musculature, and/or the head), could occur in either the presence or absence of an epileptiform discharge (ED). In lack of a systematic analysis, both MMEs and EDs were frequently observed to occur in association with arousal fluctuations. Hereby, in the same group of refractory NFLE subjects, we report a methodical neurophysiolgical investigation set out to investigate whether, and how, the arousal mechanism, monitored through visual scoring of the cyclic alternating pattern, modulates the expression of MMEs and EDs. METHODS: The relationship of MMEs, EDs and arousal fluctuation was assessed in subjects explored using implanted electrodes. RESULTS: The occurrence of both EDs and MMEs was associated with higher level of arousal (p < 0.0001). Multivariate logistic regression analysis shows a significant effect of interaction of EDs and MMEs during CAP sleep (p < 0.001). CONCLUSIONS: Both MMEs and EDs are associated with arousal. We suggest that recurrence of EDs in itself can induce an increase in arousal level, which in turn, through a gate effect, facilitate the occurrence of MMEs. Thus, MMEs wouldn't be a direct effect of EDs, but rather originate from an indirect effect related to loss of cortical inhibition, which is secondary to arousal. In this perspective MMEs may be regarded as the result of aspecific dishinibition, triggered by internal epileptiform stimuli, of innate motor patterns generated by central pattern generators (CPGs). The CPG system might represent, through arousal facilitation, the substrate of the heterogeneous expression of MMEs in NFLE.

Sleep-related minor motor events in nocturnal frontal lobe epilepsy.

PURPOSE: Nocturnal frontal lobe epilepsy (NFLE) is characterized by a wide spectrum of sleep-related motor manifestations of increasing complexity, ranging from major episodes to brief motor events (minor motor events, MMEs). NFLE patients may exhibit a large quantity of MMEs in the form of short-lasting stereotyped movements. Whereas major episodes are considered epileptiform manifestations, it remains unclear whether the MMEs are related to epileptiform discharges (EDs). METHODS: To study the relation between EDs and the occurrence of MMEs, we report a detailed neurophysiolgical evaluation in NFLE subjects explored by using implanted electrodes. RESULTS: The median value of ED-related movements was 71.8%. Motor expression in relation to epileptiform discharge was surprisingly variable; no peculiar expression of MMEs could be attributed to the presence of EDs. CONCLUSIONS: Our data suggest that ED-associated MMEs are extremely polymorphous, and no univocal relation to EDs can be identified. We hypothesize that MMEs are not a direct effect of epileptiform discharge (i.e., not epileptic in origin), but the result of aspecific disinhibition of innate motor patterns. We warn clinicians that the epileptic nature of minimal motor phenomena in NFLE cannot be established on the clinical phenomenology of the event.

AlphaCaMKII and NMDA-receptor subunit expression in epileptogenic cortex from human periventricular nodular heterotopia.

PURPOSE: Periventricular nodular heterotopia (PNH) is the most common human brain dysgenesis, very frequently characterized by focal drug-resistant epilepsy. To understand the cellular mechanisms underlying its intrinsic hyperexcitability, we investigated the expression of glutamate-receptor subunits and related proteins in four human patients affected by PNH. METHODS: PNH was diagnosed by means of magnetic resonance imaging. The epileptogenic area was revealed by depth electrode recordings and removed during epilepsy surgery. Sections from the removed cerebral tissue were analyzed by means of immunocytochemistry (ICC), with antibodies directed against N-methyl-d-aspartate (NMDA)-receptor subunits, the alpha subunit of the Ca2+/calmodulin-dependent kinase II (alphaCaMKII), and its active phosphorylated form. RESULTS: The ICC data demonstrated that the subcortical heterotopic nodules were consistently characterized by lower expression of alphaCaMKII and its activated form. In more pronounced cases (i.e., when the extension of the nodules to the neocortex determined clear layering abnormalities), the heterotopic tissue also was characterized by a decreased expression of NMDA-receptor subunits, which was particularly evident in the dendritic compartment. CONCLUSIONS: These data suggest the existence of an alteration of alphaCaMKII and the NMDA-receptor complex in the epileptogenic brain tissue of human PNH, which may play a role in the basic mechanisms of hyperexcitability associated with this brain dysgenesis.