Walter Silva

Efficacy of ketogenic diet in severe refractory status epilepticus initiating fever induced refractory epileptic encephalopathy in school age children (FIRES)

Purpose:  Fever induced refractory epileptic encephalopathy in school age children (FIRES) is a devastating condition initiated by prolonged perisylvian refractory status epilepticus (SE) triggered by fever of unknown cause. SE may last more than 1 month, and this condition may evolve into pharmacoresistant epilepsy associated with severe cognitive impairment. We aimed to report the effect of ketogenic diet (KD) in this condition.

Auditory Feedback Differentially Modulates Behavioral and Neural Markers of Objective and Subjective Performance When Tapping to Your Heartbeat

Interoception, the perception of our body internal signals, plays a key role in maintaining homeostasis and guiding our behavior. Sometimes, we become aware of our body signals and use them in planning and strategic thinking. Here, we show behavioral and neural dissociations between learning to follow ones own heartbeat and metacognitive awareness of ones performance, in a heartbeat-tapping task performed before and after auditory feedback. The electroencephalography amplitude of the heartbeat-evoked potential in interoceptive learners, that is, participants whose accuracy of tapping to their heartbeat improved after auditory feedback, was higher compared with non-learners. However, an increase in gamma phase synchrony (30–45 Hz) after the heartbeat auditory feedback was present only in those participants showing agreement between objective interoceptive performance and metacognitive awareness. Source localization in a group of participants and direct cortical recordings in a single patient identified a network hub for interoceptive learning in the insular cortex. In summary, interoceptive learning may be mediated by the right insular response to the heartbeat, whereas metacognitive awareness of learning may be mediated by widespread cortical synchronization patterns.

Dietary therapy is not the best option for refractory nonsurgical epilepsy

The ketogenic diet (KD) is currently a well‐established treatment for patients with medically refractory, nonsurgical epilepsy. However, despite its efficacy, the KD is highly restrictive and constitutes a treatment with serious potential adverse effects, and often with difficulties in its implementation and compliance. Patients on the KD require strict follow‐up and constant supervision by a medical team highly experienced in its management in order to prevent complications. Other alternative treatments for patients with refractory epilepsy include vagus nerve stimulation (VNS), new‐generation antiepileptic drugs (AEDs), corpus callosotomy (CC), and responsive focal cortical stimulation (RNS). In this review, we explain not only the difficulties of the KD as a therapeutic option for refractory epilepsy but also the benefits of other therapeutic strategies, which, in many cases, have proven to have better efficacy than the KD itself.

Attention, in and Out: Scalp-Level and Intracranial EEG Correlates of Interoception and Exteroception

Interoception, the monitoring of visceral signals, is often presumed to engage attentional mechanisms specifically devoted to inner bodily sensing. In fact, most standardized interoceptive tasks require directing attention to internal signals. However, most studies in the field have failed to compare attentional modulations between internally- and externally-driven processes, thus probing blind to the specificity of the former. Here we address this issue through a multidimensional approach combining behavioral measures, analyses of event-related potentials and functional connectivity via high-density electroencephalography, and intracranial recordings. In Study 1, 50 healthy volunteers performed a heartbeat detection task as we recorded modulations of the heartbeat-evoked potential (HEP) in three conditions: exteroception, basal interoception (also termed interoceptive accuracy), and post-feedback interoception (sometimes called interoceptive learning). In Study 2, to evaluate whether key interoceptive areas (posterior insula, inferior frontal gyrus, amygdala, and somatosensory cortex) were differentially modulated by externally- and internally-driven processes, we analyzed human intracranial recordings with depth electrodes in these regions. This unique technique provides a very fine grained spatio-temporal resolution compared to other techniques, such as EEG or fMRI. We found that both interoceptive conditions in Study 1 yielded greater HEP amplitudes than the exteroceptive one. In addition, connectivity analysis showed that post-feedback interoception, relative to basal interoception, involved enhanced long-distance connections linking frontal and posterior regions. Moreover, results from Study 2 showed a differentiation between oscillations during basal interoception (broadband: 35–110 Hz) and exteroception (1–35 Hz) in the insula, the amygdala, the somatosensory cortex, and the inferior frontal gyrus. In sum, this work provides convergent evidence for the specificity and dynamics of attentional mechanisms involved in interoception.

Epilepsia partialis continua associated with levamisole.

Epilepsia partialis continua is defined as a spontaneous regular or irregular clonic muscular twitching affecting a limited part of the body, occurring for a minimum of 1 hour and recurring at intervals of less than 10 seconds. Levamisole is used as an immunomodulating medication in patients with recurrent aphthous ulcers. Evidence suggests that it can induce multifocal inflammatory leukoencephalopathy. We describe the clinical neuroimaging and ictal electroencephalographic findings in an adolescent with epilepsia partialis continua caused by the administration of levamisole with cortical and subcortical lesions. To our knowledge, this is the first report that describes the association of epilepsia partialis continua cortical lesions detected by magnetic resonance imaging and levamisole that were not previously described.

Classification of Normal and Pre-Ictal EEG Signals Using Permutation Entropies and a Generalized Linear Model as a Classifier

In this contribution, a comparison between different permutation entropies as classifiers of electroencephalogram (EEG) records corresponding to normal and pre-ictal states is made. A discrete probability distribution function derived from symbolization techniques applied to the EEG signal is used to calculate the Tsallis entropy, Shannon Entropy, Renyi Entropy, and Min Entropy, and they are used separately as the only independent variable in a logistic regression model in order to evaluate its capacity as a classification variable in a inferential manner. The area under the Receiver Operating Characteristic (ROC) curve, along with the accuracy, sensitivity, and specificity are used to compare the models. All the permutation entropies are excellent classifiers, with an accuracy greater than 94.5% in every case, and a sensitivity greater than 97%. Accounting for the amplitude in the symbolization technique retains more information of the signal than its counterparts, and it could be a good candidate for automatic classification of EEG signals.

Integration And Differentiation Of Neural Information Dissociate Between Conscious Percepts

At any given moment, we experience a perceptual scene as a single whole and yet we may distinguish a variety of objects within it. This phenomenon instantiates two properties of conscious perception: integration and differentiation. Integration to experience a collection of objects as a unitary percept, and differentiation to experience these objects as distinct from each other. Here we evaluated the neural information dynamics underlying integration and differentiation of perceptual contents during bistable perception. Participants listened to a sequence of tones (auditory bistable stimuli) experienced either as a single stream (perceptual integration) or as two parallel streams (perceptual differentiation) of sounds. We computed neurophysiological indices of information integration and information differentiation with electroencephalographic and intracranial recordings. When perceptual alternations were endogenously driven, the integrated percept was associated with an increase in neural information-integration and a decrease in neural differentiation across frontoparietal regions, whereas the opposite pattern was observed for the differentiated percept. However, when perception was exogenously driven by a change in the sound stream (no bistability) neural oscillatory power distinguished between percepts but information measures did not. We demonstrate that perceptual integration and differentiation can be mapped to theoretically-motivated neural information signatures, suggesting a direct relationship between phenomenology and neurophysiology.At any given moment, we experience a perceptual scene as a single whole and yet we may distinguish a variety of objects within it. This characteristic of perception instantiates two general properties of phenomenological experience: integration and differentiation. While integration is the property of experiencing a collection of objects as a unitary percept, differentiation is the property of experiencing these objects as different percepts. Little is known about how these two phenomenological properties are dynamically indexed by the brain in terms of information processing. Here we evaluated the dynamics of neural information underlying phenomenological integration and differentiation in bistable perception. Participants listened to auditory bistable stimuli, a sequence of tones experienced either as a (single) integrated percept (phenomenological integration) or as two (parallel) differentiated percepts (phenomenological differentiation). We computed neurophysiological indices of information integration and information differentiation with electroencephalographic and direct cortical recordings in human participants. We focused specifically on the gamma-band dynamics within the frontoparietal network, commonly implicated in conscious processing. In electrical recordings at the scalp and intracranially, the phenomenologically integrated percept generated an increase in neural information integration and a decrease in differentiation between frontal and parietal regions, whereas the opposite pattern was observed for the phenomenologically differentiated percept. This effect was not observed in the auditory control task. Furthermore, this dissociation was not observed when computing traditional measures of neural oscillatory integration (phase synchronization) within the same frontoparietal network and frequency range. However, this frontoparietal phase synchrony was able to distinguish between a stable perceptual window and the transitional period between the two percepts. These theoretically-motivated neural indices of information dynamics dissociated phenomenological integration and differentiation that indices of oscillatory dynamics did not. By incorporating theoretically motivated measures of information theory in the characterization of perceptual content, we contribute to the construction of a testable framework to investigate the neuroscience of conscious experience.

Intracranial high-γ connectivity distinguishes wakefulness from sleep

ABSTRACT Neural synchrony in the &ggr;‐band is considered a fundamental process in cortical computation and communication and it has also been proposed as a crucial correlate of consciousness. However, the latter claim remains inconclusive, mainly due to methodological limitations, such as the spectral constraints of scalp‐level electroencephalographic recordings or volume‐conduction confounds. Here, we circumvented these caveats by comparing &ggr;‐band connectivity between two global states of consciousness via intracranial electroencephalography (iEEG), which provides the most reliable measurements of high‐frequency activity in the human brain. Non‐REM Sleep recordings were compared to passive‐wakefulness recordings of the same duration in three subjects with surgically implanted electrodes. Signals were analyzed through the weighted Phase Lag Index connectivity measure and relevant graph theory metrics. We found that connectivity in the high‐&ggr; range (90–120 Hz), as well as relevant graph theory properties, were higher during wakefulness than during sleep and discriminated between conditions better than any other canonical frequency band. Our results constitute the first report of iEEG differences between wakefulness and sleep in the high‐&ggr; range at both local and distant sites, highlighting the utility of this technique in the search for the neural correlates of global states of consciousness. HighlightsIEEG recordings overcome the methodological limitations of other techniques.IEEG high‐&ggr; connectivity is higher during wakefulness than during sleep.It distinguishes between states better than any other canonical frequency band.Connectivity differences are present at both local and distant sites.

Cirugía de la epilepsia de la región posterior: pronóstico y estrategias en dos centros de Argentina

Resumen Introduccion Las epilepsias de la region posterior (ERP) comprenden las que comprometen los lobulos occipitales, la region parietal por detras del surco poscentral y los limites temporales posteriores, y corresponden a menos del 10% de epilepsias focales. La cirugia de este tipo de epilepsias es poco frecuente, debido principalmente a la alta proporcion de areas elocuentes de esta region. Objetivo Evaluar los resultados y estrategias de la cirugia en ERP en nuestro medio. Material y metodos Se analizaron retrospectivamente pacientes con epilepsia refractaria sometidos a cirugia de la ERP entre los anos 2005 y 2008. La evaluacion prequirurgica fue realizada mediante la semiologia ictal, IRM de alta resolucion, EEG interictal, V-EEG ictal, evaluacion neuropsicologica, EEG invasivo y mapeo funcional por estimulacion electrica. El pronostico de crisis fue evaluado con escala de Engel, con un seguimiento minimo de un ano. Resultados Seis pacientes fueron incluidos, con un seguimiento medio de 2 anos (1 a 3 anos). La edad promedio fue de 23 anos (1 a 33 anos), con una duracion media de la epilepsia de 18 anos (0 a 33 anos). Las etiologias fueron: tumores de bajo grado (2 pacientes), displasias corticales focales (2) y gliosis (2). Durante el seguimiento, 3 pacientes se encontraban libres de crisis, uno continua con auras y 2 presentaron una reduccion mayor del 50% de las crisis. Dos pacientes presentaron exacerbacion de un deficit neurologico previo (hemianopsia). Conclusion La cirugia de la ERP es posible realizarla en nuestro medio, presenta un buen pronostico de crisis y el deficit posquirurgico es aceptable.