The white matter (WM) is considered critical for linking cortical processing networks necessary for cognition. The aim of this study was to assess diffusion tensor imaging (DTI) measures of regional WM in children with nonlesional localization-related epilepsy in comparison to controls, and to determine the relation between lobar WM and neuropsychological performance.
Forty children with nonlesional localization-related epilepsy and 25 healthy controls with no neurological or psychiatric disorders and normal magnetic resonance imaging (MRI) were recruited. All patients and controls underwent neuropsychological testing that evaluated intelligence, language, memory, executive function, and motor function, as well as DTI to assess regional WM measures of fractional anisotropy (FA) and mean diffusivity (MD). The regional FA and MD were compared between patients and controls, and correlated with neuropsychological function. The relations between regional FA and MD with age at seizure onset and duration of epilepsy were assessed.
Twenty-one patients had left-sided and 19 patients had right-sided epilepsy. There were no significant differences in seizure-related variables including age at seizure onset, duration of epilepsy, seizure frequency, and number of antiepileptic medications, as well as no significant differences in neuropsychological function and DTI measures of white matter in left-sided compared to right-sided epilepsy. Therefore, all the patients with epilepsy were treated as one group. Patients with epilepsy performed significantly worse on intelligence (p < 0.001), language (p < 0.001), and executive function (p = 0.001) evaluation than controls. Patients had significantly reduced FA in left frontal (p = 0.015), right frontal (p = 0.004), left temporal (p = 0.039), right temporal (p = 0.003), right parietal (p = 0.014), and right occipital (p = 0.025) WM relative to controls. There were no significant regional WM differences (all p > 0.05) in MD between patients and controls. There was a significant positive correlation between right temporal FA with language (r = 0.535, p < 0.001) and executive function (r = 0.617, p < 0.001), as well as between body of corpus callosum FA with intelligence (r = 0.536, p < 0.001) and language (r = 0.529, p < 0.001) in patients. Left parietal MD was significantly correlated with language (r = −0.545, p < 0.001) in patients. FA of right temporal WM was significantly associated with age at seizure onset (t = 4.97, p < 0.001).
There was widespread regional WM abnormality in children with nonlesional localization-related epilepsy, which was associated with impaired neuropsychological function. The impairment in WM may reflect disruption in the connectivity for cortical processing networks, which is necessary for the development of cognition.
PMID: 23650911 CAMSID: cams3764
Diffusion tensor imaging; Pediatric epilepsy; Neuropsychological function
Malignant migrating partial seizures in infancy (MMPEI) is an early onset epileptic encephalopathy with few known etiologies. We sought to identify a novel cause of MMPEI in a child with MMPEI whose healthy parents were consanguineous. We used array comparative genomic hybridization (CGH) to identify copy number variants (CNVs) genome-wide and long-range PCR to further delineate the breakpoints of a deletion found by CGH. The proband had an inherited homozygous deletion of chromosome 20p13, disrupting the promoter region and first three coding exons of the gene PLCB1. Additional MMPEI cases were screened for similar deletions or mutations in PLCB1 but did not harbor mutations. Our results suggest that loss of PLCβ1 function is one cause of MMPEI, consistent with prior studies in a Plcb1 knockout mouse model that develops early onset epilepsy. We provide novel insight into the molecular mechanisms underlying MMPEI and further implicate PLCB1 as a candidate gene for severe childhood epilepsies. This work highlights the importance of pursuing genetic etiologies for severe early onset epilepsy syndromes.
Focal epilepsy; migrating partial seizures in infancy; genetics; phospholipase C beta 1 (PLCB1)
Voltage-gated ion channels are diverse and fundamental determinants of neuronal intrinsic excitability. Voltage-gated K+ (Kv) and Na+ (Nav) channels play complex yet fundamentally important roles in determining intrinsic excitability. The Kv and Nav channels located at the axon initial segment (AIS) play a unique and especially important role in generating neuronal output in the form of anterograde axonal and backpropagating action potentials, Aberrant intrinsic excitability in individual neurons within networks contributes to synchronous neuronal activity leading to seizures. Mutations in ion channel genes gives rise to a variety of seizure-related “Channelopathies”, and many of the ion channel subunits associated with epilepsy mutations are localized at the AIS, making this a hotspot for epileptogenesis. Here we review the cellular mechanisms that underlie the trafficking of Kv and Nav channels found at the AIS, and how Kv and Nav channel mutations associated with epilepsy can alter these processes.
Potassium; channel-Sodium; channel- Neuron-Subcellular; localization-Seizures
Ion channel dysfunction or “channelopathy” is a proven cause of epilepsy in the relatively uncommon genetic epilepsies with Mendelian inheritance. But numerous examples of acquired channelopathy in experimental animal models of epilepsy following brain injury have also been demonstrated. Our understanding of channelopathy has grown due to advances in electrophysiology techniques that have allowed the study of ion channels in the dendrites of pyramidal neurons in cortex and hippocampus. The apical dendrites of pyramidal neurons comprise the vast majority of neuronal surface membrane area, and thus the majority of the neuronal ion channel population. Investigation of dendritic ion channels has demonstrated remarkable plasticity in ion channel localization and biophysical properties in epilepsy, many of which produce hyperexcitability and may contribute to the development and maintenance of the epileptic state. Here we review recent advances in dendritic physiology and cell biology, and their relevance to epilepsy.
Dendrites; channelopathy; K+ channels; Na+ channels; Ca2+ channels; HCN channels; pyramidal neurons
Seizures can give rise to enduring changes that reflect alterations in gene expression patterns, intra and inter cellular signaling and ultimately network alterations that are a hallmark of epilepsy. A growing body of literature suggests that long-term changes in gene transcription associated with epilepsy are mediated via modulation of chromatin structure. One transcription factor in particular, REST (repressor element 1-silencing transcription factor), has received a lot of attention due to the possibility that it may control fundamental transcription patterns that drive circuit excitability, seizures and epilepsy. REST represses a suite of genes in the nervous system by utilizing nuclear protein complexes that were originally identified as mediators of epigenetic inheritance. Epigenetics has traditionally referred to mechanisms that allow a heritable change in gene expression in the absence of DNA mutation. However a more contemporaneous definition acknowledges that many of the mechanisms used to perpetuate epigenetic traits in dividing cells are utilized by neurons to control activity dependent gene expression.
This review will survey what is currently understood about the role of epigenetic mechanisms in epilepsy. We discuss how REST controls gene expression to effect circuit excitability and neurogenesis in epilepsy. We also discuss how the repressor MeCP2 and activator CREB regulate neuronal activity and are themselves controlled by activity. Finally we highlight possible future directions in the field of epigenetics and epilepsy.
REST; RE1; NRSF; epilepsy; epigenetics; chromatin; histone; neurogenesis; MeCP2; CREB; seizure; excitability; G9a; CoREST; SIN3; HDAC
Previous studies from our and other groups have demonstrated that the majority of γ-aminobutyric acid (GABA)A receptor subunit mutations produce mutant subunits with impaired biogenesis and trafficking. These GABAA receptor mutations include missense, nonsense, deletion, or insertion mutations that result in a frameshift with premature translation-termination codons (PTCs) and splice-site mutations. Frameshift or splice-site mutations produce mutant proteins with PTCs, thus generating nonfunctional truncated proteins. All of these mutant GABAA receptor subunits are subject to cellular quality control at the messenger RNA (mRNA) or protein level. These quality-control checkpoints shape the cell’s response to the presence of the mutant subunits and attempt to reduce the impact of the mutant subunit on GABAA receptor expression and function. The check points prevent nonfunctioning or malfunctioning GABAA receptor subunits from trafficking to the cell surface or to synapses, and help to ensure that the receptor channels trafficked to the membrane and synapses are indeed functional. However, if and how these quality control or check points impact the posttranslational modifications of functional GABAA receptor channels such as receptor phosphorylation and ubiquitination and their involvement in mediating GABAergic inhibitory synaptic strength needs to be investigated in the near future.
GABAA receptors; Nonsense mediated decay; Premature translation-termination codons; Endoplasmic reticulum associated degradation; Endoplasmic reticulum retention; Unfolded protein response; Mutation; Idiopathic generalized epilepsies
Epilepsy is a common childhood neurologic disorder, affecting 0.5 to1% of children. Increased mortality occurs due to progression of underlying disease, seizure-related accidents, suicide, status epilepticus, aspiration during seizures, and sudden unexplained death in epilepsy (SUDEP). Previous studies show mortality rates of 2.7 to 6.9 per 1000 person-years (Berg et al., 2004, Sillanpaa & Shinnar, 2010). Potential risk factors include poor seizure control, intractable epilepsy, status epilepticus, tonic-clonic seizures, mental retardation, and remote symptomatic cause of epilepsy (Berg et al., 2004, Sillanpaa & Shinnar, 2010, Walczak et al., 2001). Few population-based studies of mortality and SUDEP in childhood-onset epilepsy have been published. The purpose of this study is to report mortality and SUDEP from a 30 year population-based cohort of children with epilepsy.
The Medical Diagnostic Index of the Rochester Epidemiology Project was searched for all codes related to seizure and convulsion in children living in Olmsted County, Minnesota and of ages birth through 17 years from 1980 through 2009. The medical records of these children were reviewed to identify all those with new-onset epilepsy, and to abstract other baseline and follow-up information. Potential risk factors including seizure type, epilepsy syndrome, history of status epilepticus, the presence and severity of neurologic impairment, and epilepsy outcome was reviewed. Epilepsy outcome was characterized by seizure frequency, number of anti-seizure medications (AEDs) used, and number of AEDs failed due to lack of efficacy, and epilepsy intractability at 1, 2, 3, 5, 10, 15, and 20 years after epilepsy onset. We followed all children through their most recent visit to determine vital status, cause of death, and whether autopsy was performed.
From 1980 to 2009, there were 467 children age birth through 17 years diagnosed with epilepsy while residents of Olmsted County, MN and had follow-up beyond the time of epilepsy diagnosis. Children were followed for a median of 7.87 years after the time of diagnosis (range 0.04–29.49 years) for a total of 4558.5 person-years. Sixteen (3.4%) of the children died, or 3.51 deaths per 1000 person-years. Two deaths were epilepsy-related (12.5%) for a rate of 0.44 per 1000 person years. One of these children died of probable SUDEP and one died of aspiration during a seizure. The remaining 14 deaths (87.5%) were due to other complications of underlying disease. Several risk factors for mortality were found, including abnormal cognition, abnormal neurologic exam, structural/metabolic etiology for epilepsy, and poorly controlled epilepsy.
Epilepsy is a disease of complex etiology and multiple molecular mechanisms contribute to its development. Temporal lobe epilepsy (TLE) may result from an initial precipitating event such as hypoxia, head injury, or prolonged seizure (i.e., status epilepticus (SE)), that is followed by a latent period of months to years before spontaneous seizures occur. GABAA receptor (GABAAR) subunits changes occur during this latent period and may persist following the onset of spontaneous seizures. Research into the molecular mechanisms regulating these changes and potential targets for intervention to reverse GABAAR subunit alterations have uncovered seizure-induced pathways that contribute to epileptogenesis. Several growth or transcription factors are known to be activated by SE, including (but not limited to): Brain Derived Neurotrophic Factor (BDNF), cAMP response element binding protein (CREB), Inducible cAMP Early Repressor (ICER), and Early Growth Response factors (Egrs). Results of multiple studies suggest that these factors transcriptionally regulate GABAAR subunit gene expression in a way that is pertinent to the development of epilepsy. This article will focus on these signaling elements and describe their possible roles in gene regulatory pathways that may be critical in the development of chronic epilepsy.
Brain Derived Neurotrophic Factor (BDNF); cAMP response element binding protein (CREB); dentate gyrus (DG); Early Growth Response factors (EGRs); GABAAv receptor α1 subunit; GABAA receptor α4 subunit; hippocampus; Inducible cAMP Early Repressor (ICER); Status Epilepticus (SE)
Epilepsy is one of the most common serious neurological disorders worldwide. Our objective was to determine which economic, healthcare, neurology and epilepsy specific resources were associated with untreated epilepsy in resource-constrained settings.
A systematic review of the literature identified community-based studies in resource-constrained settings that calculated the epilepsy treatment gap, the proportion with untreated epilepsy, from prevalent active epilepsy cases. Economic, healthcare, neurology and epilepsy specific resources were taken from existing datasets. Poisson regression models with jackknifed standard errors were used to create bivariate and multivariate models comparing the association between treatment status and economic and health resource indicators. Relative risks were reported.
Forty-seven studies of 8285 individuals from 24 countries met inclusion criteria. Bivariate analysis demonstrated that individuals residing in rural locations had significantly higher risks of untreated epilepsy [Relative Risk(RR)=1.63; 95% confidence interval(CI):1.26,2.11]. Significantly lower risks of untreated epilepsy were observed for higher physician density [RR=0.65, 95% CI:0.55,0.78], presence of a lay [RR=0.74, 95%CI:0.60,0.91] or professional association for epilepsy [RR=0.73, 95%CI:0.59,0.91], or post-graduate neurology training program [RR=0.67, 95%CI:0.55, 0.82]. In multivariate models, higher physician density maintained significant effects [RR=0.67; 95%CI:0.52,0.88].
Even among resource-limited regions, people with epilepsy in countries with fewer economic, healthcare, neurology and epilepsy specific resources are more likely to have untreated epilepsy. Community-based epilepsy care programs have improved access to treatment but in order to decrease the epilepsy treatment gap, poverty and inequalities of healthcare, neurological and epilepsy resources must be dealt with at the local, national, and global levels.
epilepsy; treatment gap; resource-limited settings; cross-national analysis
Polymicrogyria; cerebral cortex; magnetic resonance imaging; brain malformation
Interictal electroencephalography (EEG) has clinically meaningful limitations in its sensitivity and specificity in the diagnosis of epilepsy because of its dependence on the occurrence of epileptiform discharges. We have developed a computer-aided diagnostic (CAD) tool that operates on the absolute spectral energy of the routine EEG and has both substantially higher sensitivity and negative predictive value than the identification of interictal epileptiform discharges. Our approach used a multilayer perceptron to classify 156 patients admitted for video-EEG monitoring. The patient population was diagnostically diverse with 87 diagnosed with either generalized or focal seizures. The remainder was diagnosed with non-epileptic seizures. The sensitivity was 92% (95% CI: 85–97%) and the negative predictive value was 82% (95% CI: 67%–92%). We discuss how these findings suggest that this CAD can be used to supplement event-based analysis by trained epileptologists.
Epilepsy; machine learning; prediction; non-epileptic seizure; computer aided diagnostics
Rapamycin (RAP) has certain antiepileptogenic features. However, it is unclear whether these effects can be explained by the anticonvulsant action of RAP, which has not been studied yet. To address this question, we tested potential anticonvulsant effects of RAP in immature and adult rats using different seizure models and treatment paradigms. In addition, we studied changes in the expression of neuropeptide Y (NPY) induced by RAP, which may serve as an indirect target of the RAP action.
A complex approach was adopted to evaluate the anticonvulsant potential of RAP: We used flurothyl-, pentylenetetrazole (PTZ)-, NMDA-, and kainic acid (KA)-induced seizures to test the effects of RAP using different pretreatment protocols in immature and adult rats. We also evaluated expression of NPY within the primary motor cortex, hippocampal CA1, and dentate gyrus (DG) after different pretreatments with RAP in immature rats.
We found that (1) RAP administered with short-term pretreatment paradigms has a weak anticonvulsant potential in the seizure models with compromised inhibition. (2) Lack of RAP efficacy correlates with decreased NPY expression in the cortex, CA1 and DG. Specifically in immature rats, a single dose of RAP (3 mg/kg) four or 24 hrs prior to seizure testing had anticonvulsant effects against PTZ-induced seizures. In the flurothyl seizure model only the four-hour pretreatment with RAP was anticonvulsant in the both age groups. Short-term pretreatments with RAP had no effects against NMDA- and KA-induced seizures tested in immature rats. Long-term pretreatments with RAP over eight days did not show beneficial effect in all tested seizure models in developing rats. Moreover, the long-term pretreatment with RAP had a slight proconvulsant effect on KA-induced seizures. In immature rats, any lack of anticonvulsant effect (including proconvulsant effect of multiple doses of RAP) was associated with downregulation of NPY expression in the cortex and DG. In immature animals, after a single dose of RAP with 24 hrs delay, we found a decrease of NPY expression in CA1 and DG.
Our data show a weak age-, treatment paradigm-, and model-specific anticonvulsant effects of RAP as well as loss of those effects after long-term RAP pretreatment associated with downregulation of NPY expression. These findings suggest that RAP is a poor anticonvulsant and may have beneficial effects only against epileptogenesis. In addition, our data present new insights into mechanisms of RAP action on seizures indicating a possible connection between mTOR signaling and NPY system.
seizures; flurothyl; pentylenetetrazole; NMDA; kainic acid
Accumulating data have demonstrated that seizures induced by kainate (KA) or pilocarpine activate the mammalian target of rapamycin (mTOR) pathway and mTOR inhibitor rapamycin can inhibit mTOR activation which subsequently has potential anti-epileptic effects. However, a preliminary study showed a paradoxical exacerbation of increased mTOR pathway activity reflected by S6 phosphorylation when rapamycin was administrated within a short period before KA injection. In the present study, we examined this paradoxical effect of rapamycin in more detail, both in normal rats and KA-injected animals.
Normal Rats or KA-treated rats pretreated with rapamycin at different time interval were sacrificed at various time points (1h, 3h, 6h, 10h, 15h and 24h) after rapamycin administration or seizure onset for Western blotting analysis. Phosphorylation of mTOR signaling target of Akt, mTOR, Rictor, Raptor, S6K and S6 were analyzed. Seizure activity was monitored behaviorally and graded according to a modified Racine scale (n=6 for each time point). Neuronal cell death was detected by Fluoro-Jade B staining.
In normal rats, we found that rapamycin showed the expected dose-dependent inhibition of S6 phosphorylation 3–24 h after injection, while a paradoxical elevation of S6 phosphorylation was observed 1 hour after rapamycin. Similarly, pretreatment with rapamycin over 10 h prior to KA inhibited the KA seizure induced mTOR activation. In contrast, rapamycin administered 1 to 6 hours before KA caused a paradoxical increase in the KA seizure-induced mTOR activation. Rats pretreated with rapamycin 1 h prior to KA exhibited an increase in severity and duration of seizures and more neuronal cell death as compared to vehicle treated groups. In contrast, rapamycin pretreated 10 h prior to KA had no effect on the seizures and decreased neuronal cell death. The paradoxical effect of rapamycin on S6 phosphorylation was correlated with upstream mTOR signaling and was reversed by pre-treatment of perifosine, an Akt inhibitor.
These data indicate the complexity of S6 regulation and its effect on epilepsy. Paradoxical effects of rapamycin need to be considered in clinical applications, such as for potential treatment for epilepsy and other neurological disorders.
Rapamycin; mTOR signaling pathway; S6 phosphorylation; Kainate; paradoxical effect
Brain drug bioavailability is regulated by the blood–brain barrier (BBB). It was recently suggested that cytochrome P450 (CYP) enzymes could act in concert with multidrug transporter proteins to regulate drug penetration and distribution into the diseased brain. The possibility that phase II metabolic enzymes could be expressed in the epileptic brain has been not evaluated. Phase II enzymes are involved in the metabolism of common antiepileptic drugs (AEDs).
Phase II enzyme UGT1A4 brain expression was evaluated in temporal lobe resections from patients with epilepsy. UGT1A4 expression was determined by western blot and immunocytochemistry in primary cultures of human drug-resistant brain endothelial human brain epileptic endothelial cells (EPI-EC)s and commercially available control cells human brain microvascular endothelial cells (HBMECs). Lack of DNA condensation measured by 4′,6-diamidino-2-phenylindole (DAPI) was used as a surrogate marker of cell viability and was correlated to UGT1A4 expression high performance liquid chromatography ultraviolet detection (HPLC-UV) was used to quantify lamotrigine metabolism by EPI-EC and HBMEC. The appearance of the specific lamotrigine metabolite, 2-n glucuronide (MET-1), was also evaluated. Lamotrigine and MET-1 levels were measured in selected surgical brain and matched blood samples.
UGT1A4 expression was observed in BBB endothelial cells and neurons. Our quantification study revealed variable levels of UGT1A4 expression across the brain specimens analyzed. Neurons devoid of UGT1A4 expression displayed nuclear DAPI condensation, a sign of cellular distress. UGT1A4 overexpression in EPI-EC, as compared to HBMEC, was reflected by a proportional increase in lamotrigine metabolism. The lamotrigine metabolite, MET-1, was formed in vitro by EPI-EC and, to a lesser extent, by HBMEC. HPLC-UV measurements of brain and blood samples obtained from patients receiving lamotrigine prior to surgery revealed the presence of lamotrigine and its metabolites in the brain.
These initial results suggest the presence of a phase II enzyme in the epileptic brain. Further studies are required to fully describe the pattern of brain UGT1A4 expression in relation to clinical variables and drug resistance.
UGT1A4; Phase II metabolism; Lamotrigine; Antiepileptic drugs; Cerebrovasculature; Seizures
The endocannabinoid system is known to modulate seizure activity in several in vivo and in vitro models, and CB1-receptor activation is anticonvulsant in the rat pilocarpine model of acquired epilepsy (AE). In these epileptic rats, a unique redistribution of the CB1 receptor occurs within the hippocampus; however, an anatomically inclusive analysis of the effect of status epilepticus (SE)–induced AE on CB1 receptors has not been thoroughly evaluated. Therefore, statistical parametric mapping (SPM), a whole-brain unbiased approach, was used to study the long-term effect of pilocarpine-induced SE on CB1-receptor binding and G-protein activation in rats with AE.
Serial coronal sections from control and epileptic rats were cut at equal intervals throughout the neuraxis and processed for [3H]WIN55,212-2 (WIN) autoradiography, WIN-stimulated [35S]GTPγS autoradiography, and CB1-receptor immunohistochemistry (IHC). The autoradiographic techniques were evaluated with both region of interest (ROI) and SPM analyses.
In rats with AE, regionally specific increases in CB1-receptor binding and activity were detected in cortex, discrete thalamic nuclei, and other regions including caudate-putamen and septum, and confirmed by IHC. However, CB1 receptors were unaltered in several brain regions, including substantia nigra and cerebellum, and did not exhibit regional decreases in rats with AE.
This study provides the first comprehensive evaluation of the regional distribution of changes in CB1-receptor expression, binding, and G-protein activation in the rat pilocarpine model of AE. These regions may ultimately serve as targets for cannabinomimetic compounds or manipulation of the endocannabinoid system in epileptic brain.
Pilocarpine; Acquired epilepsy; Immunohistochemistry; [35S]GTPγS autoradiography; [3H]WIN55; 212-2 autoradiography; Statistical parametric mapping
Temporal lobe epilepsy is associated with the inflammatory process related to the basic mechanisms that lead to seizure susceptibility and brain damage. Platelet-activating factor (PAF), a potent, short-lived phospholipid mediator of inflammation participates in physiological signaling in the brain. However, after seizures PAF accumulates in the brain and activates intracellular signaling related with inflammation-mediated excitotoxicity and hippocampal hyperexcitability. The objective of this study is to evaluate the effect of PAF antagonism on hippocampal hyperexcitability, seizure susceptibility and neuroprotection using the kindling paradigm and pilocarpine-induced seizure damage models.
The PAF antagonist, LAU-0901 (60 mg/kg, i.p.), or vehicle was administrated each day of kindling or daily during the four weeks after status epilepticus (SE). We analyzed seizure severity, electrical activity, cellular damage and inflammation in the hippocampi of both treated groups.
LAU-0901 limits the progression of kindling and attenuates seizure susceptibility one week after the kindling procedure. Also, under the seizure-damage conditions studied here, we observed that LAU-0901 induces hippocampal neuroprotection and limits somatostatin interneuronal cell loss and inflammation.
Our results indicate that modulation of PAF over-activity attenuates seizure susceptibility, hippocampal hyperexcitability and neuroinflammation.
Kindling; epileptogenesis; platelet-activating factor; neuroinflammation; seizures; neuroprotection; somatostatin
High-frequency oscillations (HFOs) known as ripples (80–250 Hz) and fast ripples (250–500 Hz) can be recorded from macroelectrodes inserted in patients with intractable focal epilepsy. They are most likely linked to epileptogenesis and have been found in the seizure onset zone (SOZ) of human ictal and interictal recordings. HFOs occur frequently at the time of interictal spikes, but were also found independently. This study analyses the relationship between spikes and HFOs and the occurrence of HFOs in nonspiking channels.
Intracerebral EEGs of 10 patients with intractable focal epilepsy were studied using macroelectrodes. Rates of HFOs within and outside spikes, the overlap between events, event durations, and the percentage of spikes carrying HFOs were calculated and compared according to anatomical localization, spiking activity, and relationship to the SOZ.
HFOs were found in all patients, significantly more within mesial temporal lobe structures than in neocortex. HFOs could be seen in spiking as well as nonspiking channels in all structures. Rates and durations of HFOs were significantly higher in the SOZ than outside. It was possible to establish a rate of HFOs to identify the SOZ with better sensitivity and specificity than with the rate of spikes.
HFOs occurred to a large extent independently of spikes. They are most frequent in mesial temporal structures. They are prominent in the SOZ and provide additional information on epileptogenicity independently of spikes. It was possible to identify the SOZ with a high specificity by looking at only 10 min of HFO activity.
PMID: 18479382 CAMSID: cams3466
Epilepsy; High-frequency oscillations; Spikes; Seizure onset zone; Intracranial electrodes
It is not easy to determine the location of the cerebral generators and the other brain regions that may be involved at the time of an epileptic spike seen in the scalp EEG. The possibility to combine EEG recording with functional MRI scanning (fMRI) opens the opportunity to uncover the regions of the brain showing changes in metabolism and blood flow in response to epileptic spikes seen in the EEG. These regions are presumably involved in the abnormal neuronal activity at the origin of epileptic discharges. This paper reviews the methodology involved in performing such studies, including the special techniques required for recording the EEG inside the scanner and the statistical issues in analyzing the fMRI signal. We then discuss the results obtained in patients with different types of focal epileptic disorders and in patients with primary generalized epilepsy. The results in general indicate that interictal epileptic discharges may affect brain areas well beyond the presumed region in which they are generated. The noninvasive nature of this method opens new horizons in the investigation of brain regions involved and affected by epileptic discharges.
PMID: 18304255 CAMSID: cams3475
FMRI; BOLD response; Epilepsy; Spikes; Localization; Activation; Deactivation
To investigate the effect of sleep stage on the properties of high-frequency oscillations (HFOs) recorded from depth macroelectrodes in patients with focal epilepsy.
Ten-minute epochs of wakefulness (W), stage 1–2 non-REM (N1-N2), stage 3 non-REM (N3) and REM sleep (R) were identified from stereo- electroencephalography (SEEG) data recorded at 2 kHz in nine patients. Rates of spikes, ripples (>80 Hz), and fast ripples (>250 Hz) were calculated, as were HFO durations, degree of spike–HFO overlap, HFO rates inside and outside of spikes, and inside and outside of the seizure-onset zone (SOZ).
Ripples were observed in nine patients and fast ripples in eight. Spike rate was highest in N1-N2 in 5 of 9 patients, and in N3 in 4 of 9 patients, whereas ripple rate was highest in N1-N2 in 4 of 9 patients, in N3 in 4 of 9 patients, and in Win 1 of 9 patients. Fast ripple rate was highest in N1-N2 in 4 of 8 patients, and in N3 in 4 of 8 patients. HFO properties changed significantly with sleep stage, although the absolute effects were small. The difference in HFO rates inside and outside of the SOZ was highly significant (p < 0.000001) in all stages except for R and, for fast ripples, only marginally significant (p = 0.018) in W.
Rates of HFOs recorded from depth macroelectrodes are highest in non-REM sleep. HFO properties were similar in stages N1-N2 and N3, suggesting that accurate sleep staging is not necessary. The spatial specificity of HFO, particularly fast ripples, was affected by sleep stage, suggesting that recordings excluding REM sleep and wakefulness provide a more reliable indicator of the SOZ.
PMID: 18801037 CAMSID: cams3468
Intracerebral EEG; High-frequency oscillations; Sleep
Combined electroencephalography (EEG) and functional MRI (EEG-fMRI) can be useful in the evaluation of epilepsy patients. The reproducibility of EEG-fMRI findings needs to be established to consider it as a clinically valuable method. We addressed the intrasubject reproducibility of EEG-fMRI and the possible superiority of higher magnetic field strength in patients who were scanned twice.
Fifteen patients were studied: Seven had one 1.5T and one 3T scan and eight had two 3T EEG-fMRI studies. Equal numbers of events of the same interictal epileptic discharge (IED) were included, and IED-related blood oxygenation level dependent (BOLD) results were compared.
In 1.5T–3T comparisons, five patients had BOLD responses in both studies, but in four there was a better response (higher maximum t-score and larger cluster) in 3T studies. One patient had a BOLD response in the 3T study only. The remaining patient had no BOLD response in either study. In 3T–3T comparisons, results were reproducible in five of eight patients, and one patient had no response in both studies. The two remaining patients had previous extensive surgery and extremely frequent IEDs. Some of the reproduced patterns in other patients, however, differed in terms of maximum t-score and cluster size.
EEG-fMRI appears to provide reasonable reproducibility, although repeated studies may show differences. The absence of BOLD response seems to be reproducible as well. EEG-fMRI results tend to benefit from higher field scanners (3T over 1.5T). Further studies are needed to determine if reproducibility depends on specific clinical, electrographic, or anatomic findings.
PMID: 21054351 CAMSID: cams3391
EEG-fMRI; Reliability; Localization; Blood oxygenation level dependent; Epilepsy surgery
Impaired consciousness in epilepsy has a major negative impact on quality of life. Prior work suggests that complex partial seizures (CPS) and generalized tonic-clonic seizures (GTCS), which both cause loss of consciousness, affect similar fronto-parietal networks. Milder involvement in CPS than in GTCS may spare some simple behavioral responses, resembling the minimally conscious state. However, this difference in responses has not been rigorously tested previously. During video/EEG monitoring, we administered a standardized prospective testing battery including responses to questions and commands, as well as tests for reaching/grasping a ball and visual tracking in 27 CPS (14 patients) and 7 GTCS (6 patients). Behavioral results were analyzed in the ictal and post-ictal periods based on video review. During both CPS and GTCS, patients were unable to respond to questions or commands. However, during CPS patients often retain minimally conscious ball grasping and visual tracking responses. Patients were able to successfully grasp a ball in 60% or to visually track in 58% of CPS, and could carry out both activities in 52% of CPS. In contrast, during GTCS preserved ball grasp (10%), visual tracking (11%) or both (7%) were all significantly less than in CPS. Post-ictal ball grasping and visual tracking were also somewhat better following CPS than GTCS. These findings suggest that impaired consciousness in CPS is more similar to minimally conscious state than to coma. Further work may elucidate the specific brain networks underlying relatively spared functions in CPS, ultimately leading to improved treatments aimed at preventing impaired consciousness.
Consciousness; Epilepsy; Complex Partial Seizures; Generalized Tonic-Clonic Seizures; Visual Tracking; Minimally Conscious State; Vegetative State
Exclusive right hemisphere language lateralization is rarely observed in the Wada angiography results of epilepsy surgery patients. Cortical stimulation mapping (CSM) is infrequently performed with such patients, as most undergo non-dominant left hemisphere resections, which are presumed not to pose any risk to language. Early language reorganization is typically assumed in such individuals, taking left hemisphere epileptiform activity as confirmation of change resulting from a pathological process. We present data from CSM and Wada studies demonstrating that right hemisphere language occurs in the absence of left hemisphere pathology, suggesting it can exist as a normal, but rare variant, in some individuals. Further, these data confirm the Wada test findings of atypical dominance.
Cortical stimulation mapping data were examined for all right hemisphere surgical patients with right hemisphere speech at our Center between 1974 and 2006. Out of 1209 interpretable Wada procedures, 89 (7.4%) patients had exclusive right hemisphere speech, and 21 (1.7%) of these patients underwent surgery involving the right hemisphere. Language site location was determined by examining intraoperative photographs, and site distribution was statistically compared to published findings from left hemisphere language dominant patients (Ojemann et al., 1989).
Language cortex was identified in the right hemisphere during CSM for all patients with available data. All sites could be classified in superior or middle temporal gyri, inferior parietal lobe, or inferior frontal gyrus; all of which were common zones where language was identified in the left hemisphere dominant comparison sample.
Results suggest: 1) the Wada procedure is a valid measure for identifying right hemisphere language processing without any false lateralization found in the patients mapped with CSM (i.e., a positive Wada is 100% sensitive for finding RH language sites), and 2) the distribution of language sites is consistent across right hemisphere and left hemisphere language dominant patients, supporting the theory that right hemisphere language can occur as a normal variant of language lateralization.
atypical language lateralization; epilepsy surgery; Wada; cortical stimulation mapping
Previous studies have documented a synaptic translocation of calcineurin (CaN) and increased CaN activity following status epilepticus (SE), however the cellular effect of these changes in CaN in the pathology of SE remains to be elucidated. This study examined a CaN-dependent modification of the dendritic cytoskeleton. CaN has been shown to induce dephosphorylation of cofilin, an actin depolymerization factor. The ensuing actin depolymerization can lead to a number of physiological changes that are of interest in SE.
SE was induced by pilocarpine injection, and seizure activity was monitored by video-EEG. Subcellular fractions were isolated by differential centrifugation. CaN activity was assayed using a para-nitrophenol phosphate assay protocol. Cofilin phosphorylation was assessed using phosphocofilin-specific antibodies. Cofilin-actin binding was determined by co-immunoprecipitation, and actin polymerization was measured using a triton-solubilization protocol. Spines were visualized using a single-section rapid Golgi impregnation procedure.
The immunoreactivity of phosphocofilin decreased significantly in hippocampal and cortical synaptosomal samples after SE. SE-induced cofilin dephosphorylation could be partially blocked by the pre-injection of CaN inhibitors. Cofilin activation could be further demonstrated by increased actin-cofilin binding and a significant depolymerization of neuronal actin, both of which were also blocked by CaN inhibitors. Finally, we demonstrated a CaN-dependent loss of dendritic spines histologically.
The data demonstrate a CaN-dependent, cellular mechanism through which prolonged seizure activity results in loss of dendritic spines via cofilin activation. Further research into this area may provide useful insights into the pathology of SE and epileptogenic mechanisms.
Calcineurin; epilepsy; cofilin; epileptogenesis; cognitive function
Idiopathic generalized epilepsy (IGE) is characterized by electroencephalography (EEG) recordings with generalized spike wave discharges (GSWDs) arising from normal background activity. Although GSWDs are the result of highly synchronized activity in the thalamocorti-cal network, EEG without GSWDs is believed to represent normal brain activity. The aim of this study was to investigate whether thalamocortical interactions are altered even during GSWD-free EEG periods in patients with IGE.
A GSWD-related group analysis was performed in 12 IGE patients to define seeds in areas involved during GSWDs. EEG–functional magnetic resonance imaging (fMRI) datasets from 22 IGE patients without GSWDs during the investigation and 30 age-matched healthy controls were then selected to investigate functional connectivity in GSWD-related areas. Blood oxygen level dependent (BOLD) signal changes were extracted from seeds defined by the GSWD-related group analysis. The averaged time course within each seed was used to detect brain regions with BOLD signal correlated with the seed. Group differences between patients and controls were estimated.
The GSWD-related group analysis showed BOLD activation in the thalamus, the frontomesial cortex, and the cerebellum and BOLD deactivation in default mode areas. For the connectivity analysis, eight seeds were placed bilaterally in the thalamus, mesial frontal cortex, precuneus, and cerebellum. The functional connectivity analysis of these seeds did not show clearly altered functional connectivity for patients versus controls.
The results underscore the paroxysmal nature of GSWDs: Although GSWDs are characterized by highly synchronized activity in the thalamocortical network, the functional connectivity in areas involved during GSWDs does not demonstrate abnormality in GSWD-free periods.
PMID: 21269293 CAMSID: cams3392
EEG-fMRI; Functional connectivity; BOLD response; IGE; Resting state
PMID: 20331719 CAMSID: cams3399