Detection of epileptic activity in absence of EEG interictal epileptic discharges

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Abstracts / Clinical Neurophysiology 127 (2016) e18–e132

Quantitative EEG features predict outcome in postanoxic electrographic status epilepticus—B.J. Ruijter a, M.J.A.M. van Putten a,b, J. Hofmeijer a,c (a Clinical Neurophysiology, MIRA – Institute for Biomedical Technology and Technical Medicine, University of Twente, The Netherlands, b Departments of Neurology and Clinical Neurophysiology, Medisch Spectrum Twente, Enschede, The Netherlands, c Department of Neurology, Rijnstate Hospital, Arnhem, The Netherlands) Objective: To identify quantitative EEG features with prognostic significance in patients with postanoxic electrographic status epilepticus. Methods: From continuous EEG recordings of 46 subsequent patients with electrographic status epilepticus after cardiac arrest, five-minute epochs were automatically selected every hour. We assessed background continuity evolution from these epochs using a quantitative parameter. If epochs were visually classified as epileptiform, additional features were extracted, including relative discharge power, interdischarge suppression ratio, correlation between discharge waveforms, coherence, and Shannon entropy. Outcome at three months was categorized as good (Cerebral Performance Category 1–2) or poor (3–5). Results: Ten patients had a good outcome. All 27 patients with status epilepticus before reaching background continuity had a poor outcome. As compared with patients with good outcome, seizure patterns of patients with poor outcome showed higher relative discharge power (0.35 vs. 0.10, p < 0.001), higher interdischarge suppression ratio (0.32 vs. 0.07, p < 0.001), higher discharge waveform correlation (0.63 vs. 0.52, p < 0.001), higher coherence (0.32 vs. 0.20, p < 0.001), and lower entropy (5.4 vs. 5.9, p = 0.011). Conclusions: In patients with postanoxic electrographic status epilepticus, poor outcome can be predicted by quantitative analysis of seizure patterns and background continuity evolution. Key message: Quantitative EEG helps predicting outcome in postanoxic electrographic status epilepticus. doi:10.1016/j.clinph.2015.11.140

Parallel Session 26 New perspectives about the role of interictal epileptiform discharges in epilepsy

Why is understanding of mechanisms of interictal discharges important for clinical practice—M. de Curtis (Unit of Epilepsy and Clinical Neurophysiology, Fondazione Istituto Neurologico Carlo Besta, Milano, Italy) The relationship between interictal discharges and seizures in focal epilepsies is debated. Interictal spiking and other patterns either increase or decrease ahead of a focal seizure. It is likely that interictal events with different functional meaning with respect to seizure generation exist. The identification of the neurobiological mechanisms that control interictal patterns that exert either a precipitating or a protective action in focal ictogenesis may be relevant to develop new therapeutic strategies to anticipate or abort seizures. The differences between interictal and pre-ictal unit firing and population spike patterns will be reviewed in animal model of focal seizures and epilepsy and in recordings performed with intracranial electrodes in patients suffering from drug-resistant focal epilepsies, submitted to pre-surgical evaluation. doi:10.1016/j.clinph.2015.11.141

Interictal discharges and HFOs in intra-operative electrocorticography before and after resection—M. Zijlmans a,b (a Department of Neurology, University Medical Center Utrecht, Utrecht, The Netherlands, b SEIN – Stichting Epilepsie Instellingen Nederland, Heemstede, The Netherlands) Intra-operative electrocorticography is used to tailor the resection of the presumed epileptogenic cortex. Tailoring based on epileptiform discharges like spikes is under debate, while ictiform spike patterns are generally considered pathognomonic for epileptogenic tissue and will usually yield the removal of the underlying tissue. High frequency oscillations (HFOs; ripples: 80–250 Hz and fast ripples: 250–500 Hz) are new biomarkers of epileptogenic tissue which are considered to be specific for the epileptogenic zone. We studied the effect of resection on the electrocorticography recordings and the predictive value of pre-resection and post-resection events. We found no HFOs in the resection border, unlike spikes, which can arise due to the resection. We found, however, an increase in ripples in functionally eloquent areas, and presumed these were physiological ripples. We found that residual post-resection fast ripples were the only predictor for post-surgical seizures. Postresection fast ripples are especially predictive of postsurgical outcome if the pre-resection electrocorticogram showed fast ripples. This suggests that fast ripples in the electrocorticogram could be useful for tailoring epilepsy surgery. People need to consider the effects of propofol and be able to recognize perisurgical artefacts and signal analysis could assist the clinical use of HFOs in electrocorticography. doi:10.1016/j.clinph.2015.11.142

Detection of epileptic activity in absence of EEG interictal epileptic discharges—F. Pittau a, M. Genetti b, G. Birot b, M. Tomescu b, S. Baldini b, S. Vulliémoz a, C. Michel b, M. Seeck a (a EEG and Epilepsy Unit, Neurology Department, University Hospitals and Faculty of Medicine of Geneva, Geneva, Switzerland, b Functional Brain Mapping Laboratory, Department of Fundamental Neurosciences, University of Geneva, Geneva, Switzerland) Aim: To assess if the EEGs of epileptic patients without any detectable spikes contain the voltage specific epileptic map. Methods: Fifteen patients with pharmaco-resistant focal epilepsy were included. Six minutes of resting state EEG with and without any detectable spikes were selected from long-term recording (31-channels, ref:FCz). Resting-state EEGs from 48 healthy control-subjects were also recorded. For each patient EEG, we calculated the averaged spike and its voltage map. We fitted the spike map on (i) EEG of patient with visible spikes (ii) EEG of the same patient without any visible spike and (iii) EEGs of the 48 controls. The presence of the voltage epileptic map was characterized by: mean-correlation and Global Explained Variance (GEV). For these criteria statistical differences between (1) controls and EEG with spikes, and (2) controls and EEG without spikes were evaluated. Results: The patient-specific epileptic voltage map was significantly more represented in the spike-free EEGs of patients than in EEGs of healthy controls (GEV p = 0.029; mean-correlation p = 0.032). This difference was more accentuated for patient-EEGs containing spikes (GEV p = 0.001, mean-correlation p < 0.001).

Abstracts / Clinical Neurophysiology 127 (2016) e18–e132

Discussion: Scalp EEGs of pharmaco-resistant epilepsy patients contains the epileptic voltage map (index of epileptic activity), even in absence of any detectable interictal epileptic discharges. doi:10.1016/j.clinph.2015.11.143

Parallel Session 27 Combining imaging and NIBS to study cognition and behaviour

TMS-fMRI to uncover cognition and behavior in healthy individuals—H.R. Siebner a,b (a Danish Research Center for Magnetic Resonance, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark, b Department of Neurology, Copenhagen University Hospital Bispebjerg, Copenhagen, Denmark)

A wide range of functional brain mapping techniques is widely available such as EEG, functional magnetic resonance imaging (fMRI), and PET. While these methods provide insights into spatiotemporal brain activation, they are merely correlational and therefore, no causal inferences can be made regarding human brain function. The combination of transcranial magnetic stimulation (TMS) with fMRI provides a powerful means of ‘‘causal mapping” of human brain networks. TMS during fMRI (online approach) can be used to test how focal cortex stimulation acutely modifies the activity and connectivity in the stimulated neuronal circuits. TMS and neuroimaging can also be separated in time (offline approach). Conditioning repetitive TMS before neuroimaging can give valuable insights into the causal dynamics of functional brain networks. Task-related fMRI before a TMS session can guide the location and timing of TMS. doi:10.1016/j.clinph.2015.11.144

TMS-PET and the dopaminergic system—A.P. Strafella (University of Toronto, Canada) The frontostriatal network plays an important role in controlling cognition and behavior. Recent developments in functional neuroimaging methodologies such as PET ligands along with brain stimulation techniques in humans such as transcranial magnetic stimulation (TMS) have proved to be a powerful combination for studying the fronto-striatal network directly in the human brain. Recent studies have proposed that changes in striatal dopamine level modulate certain cognitive processes and level of cognitive/behavioral impairment may be dependent on the level of dopaminergic changes. In this presentation, we will show how today brain stimulation techniques combined with neuroimaging are helping us to understand the role of frontal cortex and basal-ganglia in behaviour and cognition. doi:10.1016/j.clinph.2015.11.145

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Characterization of GABAA-receptor mediated neurotransmission in the human cortex by paired-pulse TMS-EEG—J. Király a, I. Premoli a,b, C. Zipser a, P. Belardinelli c, U. Ziemann a, F. MüllerDahlhaus a (a Department of Neurology and Stroke, and Hertie Institute for Clinical Brain Research, Eberhard-Karls-University Tübingen, Tübingen, Germany, b Department of Clinical Neurosciences, Institute of Psychiatry, Psychology and Neuroscience, King’s College London, London, UK, c Functional and Restorative Neurosurgery, University Hospital Tübingen, Eberhard-Karls-University Tübingen, Tübingen, Germany) Objective: To determine the physiology of short-interval intracortical inhibition (SICI) directly at the cortical level. Methods: We recorded a 64 channel EEG during application of a magnetic test stimulus (TS100) 2 ms after a conditioning stimulus (CS70) over the left primary motor cortex at an intensity of 100% and 70% resting motor threshold for the right APB muscle, respectively. Subjects were given a single oral dose of diazepam or baclofen in this placebo controlled, pseudo-randomized, double-blinded crossover study. Results: CS70 evoked clearly discernible and reproducible EEG potentials (TEPs) similar to TS100, i.e. a P25, N45, P70, N100, and P180 potential. In the paired-pulse condition, corrected for these CS70-induced TEPs, CS70 modulated all TS-evoked EEG potentials, i.e. suppressed the P25, N45, N100, and P180, whereas the P70 was increased. Preliminary analyses of the pharmacological data from eleven subjects further suggested an increase of SICI of the P25 potential by diazepam, in line with a GABAA-receptor mediated mechanism. Conclusions: Our data provide evidence for the physiological mechanisms of SICI at the level of the human cortex with high temporal and spatial resolution. Key message: SICI is characterized by temporally and spatially distinct modulation of TMS-evoked EEG responses. doi:10.1016/j.clinph.2015.11.146

Efficacy of cathodal Transcranial Direct Current Stimulation in epilepsy: A proof of principle—G. Assenza, C. Campana, M. Tombini, A. Benvenga, F. Assenza, G. Di Pino, V. Di Lazzaro (Campus Biomedico University of Rome, Italy) It has been proved that Transcranial DCS (tDCS) can modulate cortical excitability, enhancing or decreasing, respectively by anodal or cathodal polarity. The short-term and lasting alterations induced by tDCS are strictly related to the charge density, duration of stimulation and the depth of neuron below the skull. Epilepsy represents a pathophysiological model of unbalanced relation between cortical excitation and inhibition. In this line, tDCS can be exploited to counterbalance the neuronal hyper-excitation through electric neural modulation. This paper aims at providing the efficacy of cathodal tDCS in reducing seizures’ frequency in drug-resistant focal epilepsy. The study was single blind and sham-controlled and compared seizure rate in the 7 days before and after tDCS and after sham in a cross-over design. 9 patients affected by focal resistant epilepsy were enrolled. After tDCS 3 out 9 patients have not any change in seizure rate. 6 patients reduced their seizure frequency >50%. No