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1.  A Computational Study of Stimulus Driven Epileptic Seizure Abatement 
PLoS ONE  2014;9(12):e114316.
Active brain stimulation to abate epileptic seizures has shown mixed success. In spike-wave (SW) seizures, where the seizure and background state were proposed to coexist, single-pulse stimulations have been suggested to be able to terminate the seizure prematurely. However, several factors can impact success in such a bistable setting. The factors contributing to this have not been fully investigated on a theoretical and mechanistic basis. Our aim is to elucidate mechanisms that influence the success of single-pulse stimulation in noise-induced SW seizures. In this work, we study a neural population model of SW seizures that allows the reconstruction of the basin of attraction of the background activity as a four dimensional geometric object. For the deterministic (noise-free) case, we show how the success of response to stimuli depends on the amplitude and phase of the SW cycle, in addition to the direction of the stimulus in state space. In the case of spontaneous noise-induced seizures, the basin becomes probabilistic introducing some degree of uncertainty to the stimulation outcome while maintaining qualitative features of the noise-free case. Additionally, due to the different time scales involved in SW generation, there is substantial variation between SW cycles, implying that there may not be a fixed set of optimal stimulation parameters for SW seizures. In contrast, the model suggests an adaptive approach to find optimal stimulation parameters patient-specifically, based on real-time estimation of the position in state space. We discuss how the modelling work can be exploited to rationally design a successful stimulation protocol for the abatement of SW seizures using real-time SW detection.
PMCID: PMC4273970  PMID: 25531883
2.  Altered information processing in children with focal epilepsies with and without intellectual disability 
Functional Neurology  2014;29(2):87-97.
The aim of this exploratory study was to investigate the relationship between focal interictal epileptiform discharges (IEDs), intellectual disability and cortical information processing in children with partial epilepsy. Two groups of patients – Group 1 (n = 9 patients) with focal IEDs and normal IQ and Group 2 (n = 10 patients) with focal IEDs and intellectual disability – were compared with 14 healthy control participants. A computerized choice reaction time task (go/no-go paradigm) was performed and event-related potentials (ERPs) were recorded. When an IED occurred during the period between the presentation of the stimulus and the response, the response was defined as a response with IED. Omission errors, commission errors and reaction time were evaluated in temporal relationship to IEDs.
The Group 1 patients did not differ from the healthy children in neurophysiological functions and ERP amplitudes. The Group 2 children showed inferior performances in verbal learning and memory, cognitive flexibility and selective attention, and were characterized by low ERP amplitudes compared with the epilepsy patients with normal IQ and the healthy children. We were not able to identify any significant relationship between IEDs and cognitive functions in either group of patients. Our findings suggest that the impact of IEDs on the overall intellectual abilities of epilepsy patients may not be as significant as previously thought. Moreover, it is likely that abnormalities in cognitive information processing as revealed by lower ERP amplitudes, occurrence of IEDs, and intellectual disabilities may represent common abnormal processes and may not be causally related to each other.
PMCID: PMC4198165  PMID: 25306118
epilepsy; go/no-go; intellectual disability; mismatch negativity; visual evoked potentials
3.  Dynamic Imaging of Coherent Sources Reveals Different Network Connectivity Underlying the Generation and Perpetuation of Epileptic Seizures 
PLoS ONE  2013;8(10):e78422.
The concept of focal epilepsies includes a seizure origin in brain regions with hyper synchronous activity (epileptogenic zone and seizure onset zone) and a complex epileptic network of different brain areas involved in the generation, propagation, and modulation of seizures. The purpose of this work was to study functional and effective connectivity between regions involved in networks of epileptic seizures. The beginning and middle part of focal seizures from ictal surface EEG data were analyzed using dynamic imaging of coherent sources (DICS), an inverse solution in the frequency domain which describes neuronal networks and coherences of oscillatory brain activities. The information flow (effective connectivity) between coherent sources was investigated using the renormalized partial directed coherence (RPDC) method. In 8/11 patients, the first and second source of epileptic activity as found by DICS were concordant with the operative resection site; these patients became seizure free after epilepsy surgery. In the remaining 3 patients, the results of DICS / RPDC calculations and the resection site were discordant; these patients had a poorer post-operative outcome. The first sources as found by DICS were located predominantly in cortical structures; subsequent sources included some subcortical structures: thalamus, Nucl. Subthalamicus and cerebellum. DICS seems to be a powerful tool to define the seizure onset zone and the epileptic networks involved. Seizure generation seems to be related to the propagation of epileptic activity from the primary source in the seizure onset zone, and maintenance of seizures is attributed to the perpetuation of epileptic activity between nodes in the epileptic network. Despite of these promising results, this proof of principle study needs further confirmation prior to the use of the described methods in the clinical praxis.
PMCID: PMC3806832  PMID: 24194931
4.  Variability of the hemodynamic response as a function of age and frequency of epileptic discharge in children with epilepsy 
NeuroImage  2007;40(2):601-614.
EEG-fMRI is a non-invasive tool to investigate epileptogenic networks in patients with epilepsy. Different patterns of BOLD responses have been observed in children as compared to adults. A high intra- and intersubject variability of the hemodynamic response function (HRF) to epileptic discharges has been observed in adults. The actual HRF to epileptic discharges in children and its dependence on age are unknown. We analyzed 64 EEG-fMRI event types in 37 children (3 months to 18 years), 92% showing a significant BOLD response. HRFs were calculated for each BOLD cluster using a Fourier basis set. After excluding HRFs with a low signal-to-noise ratio, 126 positive and 98 negative HRFs were analyzed. We evaluated age-dependent changes as well as the effect of increasing numbers of spikes. Peak time, amplitude and signal-to-noise ratio of the HRF and the t-statistic score of the cluster were used as dependent variables. We observed significantly longer peak times of the HRF in the youngest children (0 to 2 years), suggesting that the use of multiple HRFs might be important in this group. A different coupling between neuronal activity and metabolism or blood flow in young children may cause this phenomenon. Even if the t-value increased with frequent spikes, the amplitude of the HRF decreased significantly with spike frequency. This reflects a violation of the assumptions of the General Linear Model and therefore the use of alternative analysis techniques may be more appropriate with high spiking rates, a common situation in children.
PMCID: PMC3793956  PMID: 18221891 CAMSID: cams3474
Hemodynamic response function; fMRI; Spike; Age
5.  Absence seizures: Individual patterns revealed by EEG-fMRI 
Epilepsia  2010;51(10):2000-2010.
Absences are characterized by an abrupt onset and end of generalized 3–4 Hz spike and wave discharges (GSWs), accompanied by unresponsiveness. Although previous electroencephalography–functional magnetic resonance imaging (EEG–fMRI) studies showed that thalamus, default mode areas, and caudate nuclei are involved in absence seizures, the contribution of these regions throughout the ictal evolution of absences remains unclear. Furthermore, animal models provide evidence that absences are initiated by a cortical focus with a secondary involvement of the thalamus. The aim of this study was to investigate dynamic changes during absences.
Seventeen absences from nine patients with absence epilepsy and classical pattern of 3–4 Hz GSWs during EEG-fMRI recording were included in the study. The absences were studied in a sliding window analysis, providing a temporal sequence of blood oxygen–level dependent (BOLD) response maps.
Thalamic activation was found in 16 absences (94%), deactivation in default mode areas in 15 (88%), deactivation of the caudate nuclei in 10 (59%), and cortical activation in patient-specific areas in 10 (59%) of the absences. Cortical activations and deactivations in default mode areas and caudate nucleus occurred significantly earlier than thalamic responses.
Like a fingerprint, patient-specific BOLD signal changes were remarkably consistent in space and time across different absences of one patient but were quite different from patient to patient, despite having similar EEG pattern and clinical semiology. Early frontal activations could support the cortical focus theory, but with an addition: This early activation is patient specific.
PMCID: PMC3769289  PMID: 20726875 CAMSID: cams3390
EEG-fMRI; Absence epilepsy; BOLD response; Thalamus; Cortical focus
6.  Seizure control in a patient with Dravet syndrome and cystic fibrosis☆ 
Satisfactory treatment of patients with Dravet syndrome (DS) is often difficult. Some success can be achieved with bromides, but cognitive side effects and disturbed vigilance may limit their use. Here, we present the case of a successfully treated patient with DS and remarkable features in the course of his disease: additionally to DS, the patient was diagnosed with cystic fibrosis (CF), another genetic channelopathy. Seizure freedom could be achieved under treatment with potassium bromide at the age of 15, but at the age of 20, adverse events made it necessary to stop bromide treatment. After conversion to valproic acid, the patient remained seizure-free, and neuropsychological tests demonstrated sustained improvement of cognition.
PMCID: PMC4150651
DS, Dravet syndrome; SMEI, severe myoclonic epilepsy of infancy; SCN1A, neuronal voltage-gated sodium channel subunit type 1; CF, cystic fibrosis; TAP, Tests of Attentional Performance; TMT A, Trail Making Test; CFTR, cystic fibrosis transmembrane conductance regulator; GABA, γ-aminobutyric acid; Dravet syndrome; Bromide; Cystic fibrosis
7.  Absence Seizures with Intellectual Disability as a phenotype of the 15q13.3 microdeletion syndrome 
Epilepsia  2011;52(12):e194-e198.
15q13.3 microdeletions are the most common genetic findings in Idiopathic Generalized Epilepsies identified to date, present in up to 1% of patients. In addition, 15q13.3 microdeletions have been described in patients with epilepsy as part of a complex neurodevelopmental phenotype. We analyzed a cohort of 570 patients with various pediatric epilepsies for 15q13.3 microdeletions. Screening was performed using quantitative polymerase chain reaction, deletions were confirmed by array comparative genomic hybridization. We carried out detailed phenotyping of deletion carriers. In total, we identified four pediatric patients with 15q13.3 microdeletions including one previously described patient. 2/4 deletions were de novo, 1 deletion was inherited from an unaffected parent, and in one patient, inheritance is unknown. All four patients had absence epilepsy with various degrees of intellectual disability. We suggest that absence epilepsy accompanied by intellectual disability may represent a common phenotype of the 15q13.3 microdeletion in pediatric epilepsy patients.
PMCID: PMC3270691  PMID: 22050399
Intellectual disability; IGE
8.  15q13.3 microdeletions increase risk of idiopathic generalized epilepsy 
Nature genetics  2009;41(2):160-162.
We identified 15q13.3 microdeletions encompassing the CHRNA7 gene in 12 of 1,223 individuals with idiopathic generalized epilepsy (IGE), which were not detected in 3,699 controls (joint P = 5.32 × 10−8). Most deletion carriers showed common IGE syndromes without other features previously associated with 15q13.3 microdeletions, such as intellectual disability, autism or schizophrenia. Our results indicate that 15q13.3 microdeletions constitute the most prevalent risk factor for common epilepsies identified to date.
PMCID: PMC3026630  PMID: 19136953
9.  Recurrent microdeletions at 15q11.2 and 16p13.11 predispose to idiopathic generalized epilepsies 
Brain  2009;133(1):23-32.
Idiopathic generalized epilepsies account for 30% of all epilepsies. Despite a predominant genetic aetiology, the genetic factors predisposing to idiopathic generalized epilepsies remain elusive. Studies of structural genomic variations have revealed a significant excess of recurrent microdeletions at 1q21.1, 15q11.2, 15q13.3, 16p11.2, 16p13.11 and 22q11.2 in various neuropsychiatric disorders including autism, intellectual disability and schizophrenia. Microdeletions at 15q13.3 have recently been shown to constitute a strong genetic risk factor for common idiopathic generalized epilepsy syndromes, implicating that other recurrent microdeletions may also be involved in epileptogenesis. This study aimed to investigate the impact of five microdeletions at the genomic hotspot regions 1q21.1, 15q11.2, 16p11.2, 16p13.11 and 22q11.2 on the genetic risk to common idiopathic generalized epilepsy syndromes. The candidate microdeletions were assessed by high-density single nucleotide polymorphism arrays in 1234 patients with idiopathic generalized epilepsy from North-western Europe and 3022 controls from the German population. Microdeletions were validated by quantitative polymerase chain reaction and their breakpoints refined by array comparative genomic hybridization. In total, 22 patients with idiopathic generalized epilepsy (1.8%) carried one of the five novel microdeletions compared with nine controls (0.3%) (odds ratio = 6.1; 95% confidence interval 2.8–13.2; χ2 = 26.7; 1 degree of freedom; P = 2.4 × 10−7). Microdeletions were observed at 1q21.1 [Idiopathic generalized epilepsy (IGE)/control: 1/1], 15q11.2 (IGE/control: 12/6), 16p11.2 IGE/control: 1/0, 16p13.11 (IGE/control: 6/2) and 22q11.2 (IGE/control: 2/0). Significant associations with IGEs were found for the microdeletions at 15q11.2 (odds ratio = 4.9; 95% confidence interval 1.8–13.2; P = 4.2 × 10−4) and 16p13.11 (odds ratio = 7.4; 95% confidence interval 1.3–74.7; P = 0.009). Including nine patients with idiopathic generalized epilepsy in this cohort with known 15q13.3 microdeletions (IGE/control: 9/0), parental transmission could be examined in 14 families. While 10 microdeletions were inherited (seven maternal and three paternal transmissions), four microdeletions occurred de novo at 15q13.3 (n = 1), 16p13.11 (n = 2) and 22q11.2 (n = 1). Eight of the transmitting parents were clinically unaffected, suggesting that the microdeletion itself is not sufficient to cause the epilepsy phenotype. Although the microdeletions investigated are individually rare (<1%) in patients with idiopathic generalized epilepsy, they collectively seem to account for a significant fraction of the genetic variance in common idiopathic generalized epilepsy syndromes. The present results indicate an involvement of microdeletions at 15q11.2 and 16p13.11 in epileptogenesis and strengthen the evidence that recurrent microdeletions at 15q11.2, 15q13.3 and 16p13.11 confer a pleiotropic susceptibility effect to a broad range of neuropsychiatric disorders.
PMCID: PMC2801323  PMID: 19843651
idiopathic generalized epilepsy; microdeletions; association; genetics
10.  MIPAS-Family—evaluation of a new multi-modal behavioral training program for pediatric headaches: clinical effects and the impact on quality of life 
The Journal of Headache and Pain  2010;11(3):215-225.
Several meta-analyses have demonstrated that the combination of electrical muscle activity and Temperature Biofeedback could be regarded as gold standard in chronic pediatric headaches. However, these techniques seem to be uneconomical and furthermore they are not directed to improve the social competence as well as resolve possible impairments in daily activities of the child. Therefore, multi-modal behavioral techniques have been proposed, but no studies comparing these with the gold standard were conducted. The present study compared the impact of a new multi-modal behavioral education and training program—MIPAS-Family—with a combined Biofeedback treatment, evaluating clinical efficacy as well as the effect on the quality of life (QoL) of children with chronic headaches. Thirty-four children and adolescents with recurrent headache, ranging from 7 to 16 years, were randomly assigned to the MIPAS-Family (N = 19) or the Biofeedback (N = 15) condition. All patients were diagnosed by the criteria of the International Headache Society. The children and their parents completed headache diaries, diaries of daily living activities and a QoL questionnaire (KINDL®). Both groups showed significant improvements concerning the headache intensity and headache duration. We found no significant differences in the main headache parameters between both treatments. After the treatments, the children were less disturbed by their headaches in the domains school, homework, and leisure time. In conclusion, MIPAS-Family is as effective as Biofeedback but it is more cost-effective and addresses the whole family and the daily activities.
PMCID: PMC3451914  PMID: 20376520
Pediatric headaches; Biofeedback; MIPAS-Family Program; Education; Behavioral medicine
11.  Genome-Wide Copy Number Variation in Epilepsy: Novel Susceptibility Loci in Idiopathic Generalized and Focal Epilepsies 
PLoS Genetics  2010;6(5):e1000962.
Epilepsy is one of the most common neurological disorders in humans with a prevalence of 1% and a lifetime incidence of 3%. Several genes have been identified in rare autosomal dominant and severe sporadic forms of epilepsy, but the genetic cause is unknown in the vast majority of cases. Copy number variants (CNVs) are known to play an important role in the genetic etiology of many neurodevelopmental disorders, including intellectual disability (ID), autism, and schizophrenia. Genome-wide studies of copy number variation in epilepsy have not been performed. We have applied whole-genome oligonucleotide array comparative genomic hybridization to a cohort of 517 individuals with various idiopathic, non-lesional epilepsies. We detected one or more rare genic CNVs in 8.9% of affected individuals that are not present in 2,493 controls; five individuals had two rare CNVs. We identified CNVs in genes previously implicated in other neurodevelopmental disorders, including two deletions in AUTS2 and one deletion in CNTNAP2. Therefore, our findings indicate that rare CNVs are likely to contribute to a broad range of generalized and focal epilepsies. In addition, we find that 2.9% of patients carry deletions at 15q11.2, 15q13.3, or 16p13.11, genomic hotspots previously associated with ID, autism, or schizophrenia. In summary, our findings suggest common etiological factors for seemingly diverse diseases such as ID, autism, schizophrenia, and epilepsy.
Author Summary
Epilepsy, a common neurological disorder characterized by recurrent seizures, affects up to 3% of the population. In some cases, the epilepsy has a clear cause such as an abnormality in the brain or a head injury. However, in many cases there is no obvious cause. Numerous studies have shown that genetic factors are important in these types of epilepsy, but although several epilepsy genes are known, we can still only identify the genetic cause in a very small fraction of cases. In order to identify new genes that contribute to the genetic causes of epilepsy, we searched the human genome for deletions (missing copies) and duplications (extra copies) of genes in ∼500 patients with epilepsy that are not found in control individuals. Using this approach, we identified several large deletions that are important in at least 3% of epilepsy cases. Furthermore, we found new candidate genes, some of which are also thought to play a role in other related disorders such as autism and intellectual disability. These genes are candidates for further studies in patients with epilepsy.
PMCID: PMC2873910  PMID: 20502679
12.  Developmental changes of the contingent negative variation in migraine and healthy children 
The Journal of Headache and Pain  2009;11(2):105-113.
It has been hypothesized that abnormalities of information processing in migraine may be attributed to impairment of cerebral maturation. However, the most evidences for this hypothesis have come from cross-sectional studies during childhood. We performed a longitudinal study and recorded contingent negative variation (CNV), an event-related slow cortical potential, in migraine children (n = 27) and age-matched healthy individuals (n = 23) in 1998 and 8 years later (2006). Amplitudes of all CNV components were reduced and habituation of the initial CNV (iCNV) increased in the observed time. However, the reduction of the iCNV amplitude was more pronounced in migraine patients who were in remission in 2006 and in healthy subjects and less pronounced in migraineurs with persisting headaches. Patients with the worsened migraine demonstrated the most pronounced loss of iCNV habituation in 1998 and significantly increased iCNV amplitudes in 2006. This longitudinal study supports the hypothesis of impaired cerebral maturation in migraine and shows that migraine manifestation is a key factor interfering with the natural maturation process of central information processing.
PMCID: PMC3452294  PMID: 20013021
Migraine; Contingent negative variation; Habituation; Maturation
13.  A data-driven model of the generation of human EEG based on a spatially distributed stochastic wave equation 
Cognitive Neurodynamics  2008;2(2):101-113.
We discuss a model for the dynamics of the primary current density vector field within the grey matter of human brain. The model is based on a linear damped wave equation, driven by a stochastic term. By employing a realistically shaped average brain model and an estimate of the matrix which maps the primary currents distributed over grey matter to the electric potentials at the surface of the head, the model can be put into relation with recordings of the electroencephalogram (EEG). Through this step it becomes possible to employ EEG recordings for the purpose of estimating the primary current density vector field, i.e. finding a solution of the inverse problem of EEG generation. As a technique for inferring the unobserved high-dimensional primary current density field from EEG data of much lower dimension, a linear state space modelling approach is suggested, based on a generalisation of Kalman filtering, in combination with maximum-likelihood parameter estimation. The resulting algorithm for estimating dynamical solutions of the EEG inverse problem is applied to the task of localising the source of an epileptic spike from a clinical EEG data set; for comparison, we apply to the same task also a non-dynamical standard algorithm.
PMCID: PMC2427060  PMID: 19003477
EEG; Source localization; Inverse problem
14.  Absence seizures with intellectual disability as a phenotype of the 15q13.3 microdeletion syndrome 
Epilepsia  2011;52(12):e194-e198.
15q13.3 microdeletions are the most common genetic findings identified in idiopathic generalized epilepsies to date, and they are present in up to 1% of patients. In addition, 15q13.3 microdeletions have been described in patients with epilepsy as part of a complex neurodevelopmental phenotype. We analyzed a cohort of 570 patients with various pediatric epilepsies for 15q13.3 microdeletions. Screening was performed using quantitative polymerase chain reaction; deletions were confirmed by array comparative genomic hybridization (CGH). We carried out detailed phenotyping of deletion carriers. In total, we identified four pediatric patients with 15q13.3 microdeletions, including one previously described patient. Two of four deletions were de novo, one deletion was inherited from an unaffected parent, and for one patient the inheritance is unknown. All four patients had absence epilepsy with various degrees of intellectual disability. We suggest that absence epilepsy accompanied by intellectual disability may represent a common phenotype of the 15q13.3 microdeletion in pediatric patients with epilepsy.
PMCID: PMC3270691  PMID: 22050399
Intellectual disability; Idiopathic generalized epilepsy

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