EEG/functional MRI in epilepsy: The Queen Square Experience.

The recording of EEG during functional MRI scanning (EEG/fMRI) has opened up new dimensions in brain research. The simultaneous recording of EEG activity and its temparospatial haemodynamic correlates is a powerful tool in the non-invasive mapping of normal and pathological brain function. The technological constraints imposed by having a conductor (the EEG) within the magnetic environment of the MRI scanner have been sufficiently overcome for high quality EEG recording during MRI. The initial applications of EEG/fMRI were in the study of epileptiform discharges in epilepsy. This has been rapidly followed by studies of normal EEG rhythms and evoked response in healthy subjects. The ability to map brain areas involved in the generation of epileptiform discharges recorded on the surface EEG has been shown using EEG/fMRI in patients with epilepsy. This has potential clinical applications in providing additional localizing information in the pre-surgical workup of epilepsy patients and in gaining a greater understanding of the neurobiology of interictal epileptiform discharges and epileptic seizures. In this review we address the issues in recording EEG during fMRI and review the application of EEG/fMRI in the study of patients with epilepsy at our centre.     

Intracranial EEG-fMRI analysis of focal epileptiform discharges in humans

Purpose: Combining intracranial electroencephalography (iEEG) with functional magnetic resonance imaging (fMRI) is of interest in epilepsy studies as it would allow the detection of much smaller interictal epileptiform discharges than can be recorded using scalp EEG‐fMRI. This may help elucidate the spatiotemporal mechanisms underlying the generation of interictal discharges. To our knowledge, iEEG‐fMRI has never been performed at 3 Tesla (3T) in humans. We report our findings relating to spike‐associated blood oxygen level–dependent (BOLD) signal changes in two subjects. Methods: iEEG‐fMRI at 3T was performed in two subjects. Twelve channels of iEEG were recorded from subdural strips implanted on the left posterior temporal and middle frontal lobes in a 20‐year‐old female with bilateral periventricular gray matter heterotopia. Twenty channels of iEEG were recorded bilaterally from two subdural strips laid anterior–posterior along mesial temporal surfaces in a 29‐year‐old woman with bilateral temporal seizures and mild left amygdalar enlargement on MRI. Functional MRI (fMRI) statistical maps were generated and thresholded at p = 0.01. Key Findings: No adverse events were noted. A total of 105 interictal discharges were recorded in the posterior middle temporal gyrus of Subject 1. In Subject 2, 478 discharges were recorded from both mesial temporal surfaces (n = 194 left, 284 right). The right and left discharges were modeled separately, as they were independent. Subject 1 showed spike‐associated BOLD signal increases in the left superior temporal region, left middle frontal gyrus, and right parietal lobe. BOLD decreases were seen in the right frontal and parietal lobes. In Subject 2, BOLD signal increases were seen in both mesial temporal lobes, which when left and right spikes were modeled independently, were greater on the side of the discharge. In addition, striking BOLD signal decreases were observed in the thalamus and posterior cingulate gyrus. Significance: iEEG‐fMRI can be performed at 3T with low risk. Notably, runs of only 5 or 10 min of EEG‐fMRI were performed as part of our implementation protocol, yet a significant number of epileptiform discharges were recorded, allowing meaningful analyses. With these studies, we have shown that deactivation can be seen in individual subjects with focal epileptiform discharges. These preliminary observations suggest a novel mechanism through which focal interictal discharges may have widespread cortical and subcortical influences.     

Writing epilepsy: a neurophysiological, neuropsychological and neuroimaging study

Writing epilepsy is a rare reflex syndrome in which seizures are triggered by writing. We describe a 33-year-old, right-handed man, with a history of juvenile absence epilepsy in remission and a family history of epilepsy, in whom myoclonic jerks precipitated exclusively by writing started at the age of 30. Intensive video/EEG monitoring during neuropsychological tests revealed, at about 1 minute after starting to write, a dystonic posture, followed by myoclonic jerks involving the right hand that shortly after became generalized. Concomitantly, the ictal EEG documented generalized hypersynchronous polyspike-wave discharges, maximal over the right parietocentral area. SPECT revealed an ictal hyperperfusion and interictal hypoperfusion over right parietofrontal regions, and fMRI showed extensive and intense left frontal, supplementary motor area activation, induced by writing. This case study provides some evidence supporting the hypothesis that the mechanism underlying writing-triggered seizures may be a generalized seizure process, with a focal cortical trigger zone, presumed to be the left frontal lobe as suggested by clinical and fMRI data. A relevant role played by the right hemisphere (right parietofrontal region) is postulated in the full-blown expression of reflex epileptogenesis, as supported by EEG and SPECT findings.     

Complementary use of video-electroencephalography and magnetoencephalography in frontal lobe epilepsy

PurposeThe aim of this study was to compare magnetoencephalography (MEG) and video-electroencephalography (VEEG) source localization in frontal lobe epilepsy (FLE) and determine if these methods can be complementary to each other in clinical practice.MethodThirty patients with pharmaco-resistant FLE who underwent epilepsy surgery were retrospectively enrolled. Video EEG was recorded using an IT-med system using 10/20 system. Regional localization of spikes in VEEG was defined as spikes discharged from adjacent electrodes and no further propagation to a large and/or contralateral area. Magnetoencephalography was recorded for the purpose of focus assessment. Magnetoencephalography spikes were detected for dipole localization of the epileptogenic cortex and the epileptogenic area was classified as mono- or multi-focal.ResultsRegional spike discharges were identified in the interictal VEEG of 20 patients and in the ictal VEEG of 17 patients. Thirteen patients had regional spikes in both interictal and ictal VEEG. Mono-focal localization was identified in the MEG of 20 patients. Fourteen of these patients had regional spike discharges in VEEG. In the remaining six patients, sources localization was only identified by MEG and there were no regional spike discharges either interictal or ictal VEEG.ConclusionIn clinical practice, VEEG is the routine procedure in the presurgical evaluation of FLE. However, we found six cases in which VEEG failed to locate the epileptogenic area that was identified by MEG. We therefore propose that combining VEEG and MEG will optimize the noninvasive presurgical evaluation of epileptiform activities in FLE.     

Functional neuroimaging in startle epilepsy: Involvement of a mesial frontoparietal network

Purpose: Startle epilepsy is a rare form of epilepsy with seizures triggered by unexpected stimuli. Previous studies have suggested the participation of several brain regions, such as the supplementary motor area (SMA) or the mesial aspect of the frontal and parietal lobes in the generation of startle epilepsy. However, how these brain regions interact with each other during seizures remains largely unknown. The aim of this study was to get insight into brain structures involved in startle‐induced seizures using an approach with functional neuroimaging. Methods: Four patients with startle epilepsy secondary to unexpected sounds were studied. All of them underwent a presurgical evaluation including ictal–single‐emission computed tomography/subtraction ictal SPECT coregistered to MRI (magnetic resonance imaging) (SPECT/SISCOM). We searched for areas with ictal changes of perfusion higher than two standard deviations (2 SD) above the reference. In one patient, a fluorodeoxyglucose–positron emission tomography (FDG‐PET) and an ictal electroencephalography–functional MRI (EEG‐fMRI) were also performed. In this patient, the results of FDG‐PET and sequential analysis of EEG‐fMRI were compared to SISCOM. Key Findings: All the patients had their typical startle‐induced seizures, consistent with bilateral asymmetric tonic seizures. Ictal‐EEG pattern was located over the mesial centroparietal region in all of them. In three of four patients, a significant hyperperfusion over the mesial frontocentral region was seen, involving the SMA, the perirolandic region, and the precuneus. In one patient, who had a congenital bilateral perisylvian polymicrogyria, it was located over the lateral perirolandic region. 18F‐FDG‐PET results in the patient in whom it was done, were concordant with SISCOM findings. Ictal EEG‐fMRI showed an initial activation located over the precuneus, SMA, cingulate gyrus, and the precentral/perirolandic area. Significance: By using a functional neuroimaging approach we have found that startle‐induced seizures could be generated by the interaction of a frontoparietal network located over the mesial surface of the brain.     

Tooth-brushing epilepsy with ictal orgasms.

We report a 41-year-old woman with complex reflex epilepsy in which seizures were induced exclusively by the act of tooth brushing. All the attacks occurred with a specific sensation of sexual arousal and orgasm-like euphoria that were followed by a period of impairment of consciousness. Ictal EEG demonstrated two events of epileptic seizure that were provoked after tooth brushing for 38 and 14 seconds, respectively. The interictal EEG showed epileptiform discharges over the right anterior temporal region and interictal single photon emission computed tomography (SPECT) scan showed relative hypoperfusion in the uncus of right temporal lobe. Brain magnetic resonance imaging (MRI) revealed right hippocampal atrophy. We suggest that tooth-brushing epilepsy, especially with sexual ictal manifestations, may provide insight into the cerebral pathophysiology at the right temporolimbic structure.     

Toothbrushing-induced epilepsy with structural lesions in the primary somatosensory area

We report three patients with reflex toothbrushing-induced epilepsy associated with small circumscribed structural lesions in the primary somatosensory cortex in close proximity to the hand and speech motor areas. Sensory symptoms were observed at clinical onset with localizing focal ictal and interictal epileptiform discharges on EEG. These cases refine the localization, possible mechanisms of epileptogenesis, and classification of this reflex epilepsy.     

脑电偶极子分析在痫灶切除术中的定位价值

目的探讨长程视频脑电监测和偶极子分析在痫灶切除术中的定位价值。方法对35例开颅痫灶切除术患者术前行常规脑电和长程视频脑电监测,脑电痫性放电进行偶极子分析,并与手术中硬膜下电极记录的脑电相对照。结果35例患者视频脑电图监测异常35例,有痫性放电者35例;常规脑电图异常28例,有痫性放电者18例;行常规脑电图监测无典型癫痫发作出现。两者之间脑电异常率、痫性放电阳性率、典型临床发作率都有统计学意义。以术中硬膜下电极记录为标准,头皮脑电偶极子定位异常放电灶的准确率为97%,切除病灶病理检查异常率86%。偶极子定位误差一般<15mm。结论长程视频脑电监测和头皮脑电偶极子定位癫痫起源灶可为开颅痫灶切除手术提供有价值的信息。     

Dynamic coupling between fMRI local connectivity and interictal EEG in focal epilepsy: A wavelet analysis approach

Simultaneous scalp EEG‐fMRI recording is a noninvasive neuroimaging technique for combining electrophysiological and hemodynamic aspects of brain function. Despite the time‐varying nature of both measurements, their relationship is usually considered as time‐invariant. The aim of this study was to detect direct associations between scalp‐recorded EEG and regional changes of hemodynamic brain connectivity in focal epilepsy through a time‐frequency paradigm. To do so, we developed a voxel‐wise framework that analyses wavelet coherence between dynamic regional phase synchrony (DRePS, calculated from fMRI) and band amplitude fluctuation (BAF) of a target EEG electrode with dominant interictal epileptiform discharges (IEDs). As a proof of concept, we applied this framework to seven patients with focal epilepsy. The analysis produced patient‐specific spatial maps of DRePS‐BAF coupling, which highlight regions with a strong link between EEG power and local fMRI connectivity. Although we observed DRePS‐BAF coupling proximate to the suspected seizure onset zone in some patients, our results suggest that DRePS‐BAF is more likely to identify wider ‘epileptic networks’. We also compared DRePS‐BAF with standard EEG‐fMRI analysis based on general linear modelling (GLM). There was, in general, little overlap between the DRePS‐BAF maps and GLM maps. However, in some subjects the spatial clusters revealed by these two analyses appeared to be adjacent, particularly in medial posterior cortices. Our findings suggest that (1) there is a strong time‐varying relationship between local fMRI connectivity and interictal EEG power in focal epilepsy, and (2) that DRePS‐BAF reflect different aspects of epileptic network activity than standard EEG‐fMRI analysis. These two techniques, therefore, appear to be complementary. Hum Brain Mapp 38:5356–5374, 2017. © 2017 Wiley Periodicals, Inc.     

Cognitive tasks as provocation methods in routine EEG: a multicentre field study

Objective: This study aimed to analyse the effect of neuropsychological activation methods on interictal epileptiform discharges, compared to standard activation methods, for both focal and generalized epilepsies. Methods: This was a multicentre, prospective study including 429 consecutive EEG recordings of individuals with confirmed or suspected diagnosis of epilepsy. Neuropsychological activation included reading aloud in foreign and native language, praxis and a letter cancelation task (each with a duration of three minutes). After counting interictal discharges in three‐minute time windows, activation and inhibition were assessed for each procedure, accounting for spontaneous fluctuations (95% CI) and compared to the baseline condition with eyes closed. Differences between generalized and focal epilepsies were explored. Results: Interictal epileptiform discharges were present in 59.4% of the recordings. Activation was seen during hyperventilation in 31%, in at least one neuropsychological activation method in 15.4%), during intermittent photic simulation in 13.1% and in the resting condition with eyes open in 9.9%. The most frequent single cognitive task eliciting activation was praxis (10.3%). Lasting activation responses were found in 18–25%. Significant inhibition was found in 88/98 patients with baseline interictal epileptiform discharges, and was not task‐specific. Significance: Adding a brief neuropsychological activation protocol to the standard EEG slightly increased its sensitivity in patients with either focal or generalized epilepsy. However, in unselected epilepsy patients, this effect seems only exceptionally to result in ultimate diagnostic gain, compared to standard procedures. From a diagnostic perspective, cognitive tasks should be reserved for patients with a suspicion of cognitive reflex epilepsy/seizures and probably require longer exposure times. Further research is needed to explore potential therapeutic applications of the observed inhibition of interictal epileptiform discharges by cognitive tasks in some patients.     

EEG-fMRI study of the ictal and interictal epileptic activity in patients with eyelid myoclonia with absences

Purpose: To investigate the blood oxygenation level‐dependent (BOLD) signal changes correlated with ictal and interictal epileptic discharges using electroencephalography‐correlated functional magnetic resonance imaging (EEG‐fMRI) in patients with eyelid myoclonia with absences (EMA) and then to explore the pathophysiological mechanisms of epileptic discharges and their effect on brain function. Methods: Four patients with EMA were investigated through the method of EEG‐fMRI. The characteristics of BOLD signal changes linked to ictal and interictal epileptic discharges under different states of consciousness were explored. Results: Seven sessions of EEG‐fMRI scanning in the four patients were obtained. The main regions of activation included thalamus, mesial frontal cortex, middle parietal lobe, temporal lobe, insula, midline structures, and cerebellum. Deactivations were mainly in the anterior frontal lobe, posterior parietal lobe, and posterior cingulate gyrus. Thalamic BOLD change was predominantly activation in most of our cases. The distribution of activation associated with ictal epileptic discharges was wider, and the distribution of deactivation was closer to pericortex compared with the BOLD change linked with interictal epileptic discharges. Conclusions: The activation in the thalamus may be associated with generalized spike wave in EMA; the combination of different patterns of activation with consistent pattern of deactivations (“default” pattern) in patients with EMA may prognosticate different states of consciousness in response to ictal and interictal epileptic discharges.     

Patient specific hemodynamic response functions associated with interictal discharges recorded via simultaneous intracranial EEG‐fMRI

Simultaneous collection of scalp EEG and fMRI has become an important tool for studying the hemodynamic changes associated with interictal epileptiform discharges (IEDs) in persons with epilepsy, and has become a standard presurgical assessment tool in some centres. We previously demonstrated that performing EEG‐fMRI using intracranial electrodes (iEEG‐fMRI) is of low risk to patients in our research centre, and offers unique insight into BOLD signal changes associated with IEDs recorded from very discrete sources. However, it is unknown whether the BOLD response corresponding to IEDs recorded by iEEG‐fMRI follows the canonical hemodynamic response. We therefore scanned 11 presurgical epilepsy patients using iEEG‐fMRI, and assessed the hemodynamic response associated with individual IEDs using two methods: assessment of BOLD signal changes associated with isolated IEDs at the location of the active intracranial electrode, and by estimating subject‐specific impulse response functions to isolated IEDs. We found that the hemodynamic response associated with the intracranially recorded discharges varied by patient and by spike location. The observed shape and timing differences also deviated from the canonical hemodynamic response function traditionally used in many fMRI experiments. It is recommended that future iEEG‐fMRI studies of IEDs use a flexible hemodynamic response model when performing parametric tests to accurately characterize these data. Hum Brain Mapp 36:5252–5264, 2015. © 2015 Wiley Periodicals, Inc.     

Startle-induced seizures and their relationship to epilepsy: Three case reports

Three cases of startle-induced seizures are presented. Well-established concepts of classification of startle-induced seizures (“reflex epilepsy,” “startle epilepsy,” “startle disease/hyperexplexia”) are reviewed. Difficulty in classifying the presented cases is pointed out. In two patients, seizures could be provoked during video/EEG monitoring. In both cases, there were no epileptiform discharges during the seizures, suggesting startle disease. Nevertheless, one of the patients had a history of generalized tonic-clonic seizures; in the other, generalized seizures developed after slow withdrawal of medication, indicating startle epilepsy. The third patient, by history, had reflex epilepsy. Unfortunately, provocation of seizures under controlled conditions was not possible, rendering further classification of seizures into subtypes impossible.     

Characterization of the hemodynamic modes associated with interictal epileptic activity using a deformable model‐based analysis of combined EEG and functional MRI recordings

Simultaneous electroencephalography and functional magnetic resonance imaging (EEG/fMRI) have been proposed to contribute to the definition of the epileptic seizure onset zone. Following interictal epileptiform discharges, one usually assumes a canonical hemodynamic response function (HRF), which has been derived from fMRI studies in healthy subjects. However, recent findings suggest that the hemodynamic properties of the epileptic brain are likely to differ significantly from physiological responses. Here, we propose a simple and robust approach that provides HRFs, defined as a limited set of gamma functions, optimized so as to elicit strong activations after standard model‐driven statistical analysis at the single subject level. The method is first validated on healthy subjects using experimental data acquired during motor, visual and memory encoding tasks. Second, interictal EEG/fMRI data measured in 10 patients suffering from epilepsy are analyzed. Results show dramatic changes of activation patterns, depending on whether physiological or pathological assumptions are made on the hemodynamics of the epileptic brain. Our study suggests that one cannot assume a priori that HRFs in epilepsy are similar to the canonical model. This may explain why a significant fraction of EEG/fMRI exams in epileptic patients are inconclusive after standard data processing. The heterogeneous perfusion in epileptic regions indicates that the properties of brain vasculature in epilepsy deserve careful attention. Hum Brain Mapp, 2010. © 2010 Wiley‐Liss, Inc.     

Visualizing prolonged hyperperfusion in post-stroke epilepsy using postictal subtraction SPECT

Diagnosis of post-stroke epilepsy is often challenging because of a low incidence of epileptiform abnormalities on electroencephalography (EEG). Hence, this study evaluated whether postictal subtraction single-photon emission computed tomography (SPECT) could visualize epileptic activity and act as a diagnostic modality in post-stroke epilepsy. Fifty post-stroke epilepsy patients, who had undergone Tc-99m-ECD SPECT twice (postictal and interictal), were enrolled. The postictal hyperperfusion area was identified by subtraction (postictal–interictal) SPECT and classified into two distribution types: superficial or deep-seated. Laterality and distribution of postictal hyperperfusion on subtraction SPECT were compared with stroke lesions, seizure symptoms, and epileptiform EEG findings. Forty-three of the 50 patients (86%) had hyperperfusion on subtraction SPECT and 26 (52%) had epileptiform EEG findings. Subtraction SPECT showed prolonged postictal hyperperfusion despite the relatively long interval between seizure end and postictal SPECT (median: 19.1 h, range: 2.2–112.5 h). The laterality of the hyperperfusion area had a high concordance rate with the laterality of stroke lesions (97.7%), seizure symptoms (91.9%), and epileptiform EEG findings (100%). Scalp EEG identified epileptiform activity more frequently in superficial type of SPECT, but less frequently in deep-seated type (both, P = 0.03). Postictal SPECT can be complementary to scalp EEG in endorsing the diagnosis and location of post-stroke epilepsy.     

Simultaneous EEG and fMRI recordings (EEG‐fMRI) in children with epilepsy

By combining electroencephalography (EEG) with functional magnetic resonance imaging (fMRI) it is possible to describe blood oxygenation level–dependent (BOLD) signal changes related to EEG patterns. This way, EEG‐pattern–associated networks of hemodynamic changes can be detected anywhere in the brain with good spatial resolution. This review summarizes EEG‐fMRI studies that have been performed in children with epilepsy. EEG‐fMRI studies in focal epilepsy (structural and nonlesional cases, benign epilepsy with centrotemporal spikes), generalized epilepsy (especially absence epilepsy), and epileptic encephalopathies (West syndrome, Lennox‐Gastaut syndrome, continuous spike and waves during slow sleep, and Dravet syndrome) are presented. Although EEG‐fMRI was applied mainly to localize the region presumably generating focal interictal discharges in focal epilepsies, EEG‐fMRI identified underlying networks in patients with generalized epilepsies and thereby contributed to a better understanding of these epilepsies. In epileptic encephalopathies a specific fingerprint of hemodynamic changes associated with the particular syndrome was detected. The value of the EEG‐fMRI technique for diagnosis and investigation of pathogenetic mechanisms of different forms of epilepsy is discussed.     

联合应用电生理技术对癫痫灶精确定位的研究

目的:联合应用多种电生理技术(EEG)对痫灶进行定位。方法:运用多种EEG技术对50例癫痫患者行痫灶定位,并与各种神经影像学检查方法进行比较。定位明确患者行手术治疗,标本行光镜及透射电镜检查,治疗结果以Engel疗效分级评价。结果:使用EEG技术对痫灶定位,其准确率为83.3％,以EEG技术为基础,并与神经影像学方法联合应用,痫灶定位准确率则达到100％。具有EEG异常的癫痫患者,痫灶必然伴有相应病理性损害。结论:反复、多次视频脑电(VEEG)监测,是痫灶定位的首选方法。多种类型的EEG在不同的时段进行监测,是高效、经济、安全无创,可明显提高癫痫灶的检出率及定位的准确性,提高手术疗效。     

The electroencephalogram of idiopathic generalized epilepsy

Idiopathic generalized epilepsy (IGE) is classified into several subsyndromes based on clinical and electroencephalography (EEG) features. The EEG signature of IGE is bisynchronous, symmetric, and generalized spike-wave complex; although focal, irregular, and so called "fragments" of discharges are not uncommon. Other characteristic EEG features include polyspikes, polyspike-wave discharges, occipital intermittent rhythmic delta activity, and photoparoxysmal response. Both human and animal data suggest involvement of the thalamus and the cortex in the generation of spike-wave discharges in IGE. Circadian variations of generalized epileptiform discharges are well described, and these can be useful in diagnostic confirmation. Those discharges tend to occur more often after awakening and during cyclic alternating pattern phase-A of non-rapid eye movement sleep. Activation procedures such as hyperventilation, intermittent photic stimulation, eye closure, and fixation-off are useful techniques to increase the yield of both interictal and ictal EEG abnormalities. Although not in routine use, specific triggers such as pattern stimulation and cognitive tasks may also be of value in eliciting rare reflex seizure-related EEG abnormalities. Variations of EEG abnormalities are evident between different electroclinical syndromes. EEG is also affected by certain external as well as internal factors, which should be borne in mind when interpreting EEG studies in IGE.     

视频脑电图监测对癫痫的诊断价值

目的探讨视频脑电图(Video-EEG)对癫痫的诊断价值.方法对252例发作性疾病患者进行连续12～24小时监测,其中包括清醒、睡眠及诱发试验,分析临床发作和异常放电的关系,异常放电出现的时相,癫痫分型与异常放电的关系,临床发作前脑电图的改变以及临床发作间期和发作期异常脑电图的不同表现.结果252例监测到临床发作142例,其中同时伴异常放电者为111例;252例检出异常放电187例,其中出现于睡眠期者146例;确诊的111例中103例确定了发作类型,其中25例修正了发作类型;确诊的111例监测到发作前脑电图的异常改变,表现为背景脑电波频率和波幅的改变,或者出现痫样放电;111例不同发作类型癫痫患者发作间期和发作期有不同的异常脑电图表现.结论视频脑电图可提高痫样放电的检出率,有助于癫痫的诊断及分型,有利于观察癫痫患者发作间期及发作期脑电图的表现.     

Patients with temporoparietal ictal symptoms and inferomesial EEG do not benefit from anterior temporal resection

PURPOSE: The role of posterior structural lesions leading to inadequate results after inferomesial temporal resection is well recognized. Here we present poor surgical outcome in six patients with nonlesional intractable epilepsy, well-defined focal anterior and inferomesial temporal epileptic discharges, and posterior temporoparietal symptoms. METHODS: We reviewed patient data including scalp video-EEG telemetry, intracranial EEG recording, magnetic resonance imaging (MRI) sequences (1.5 Tesla), and single-photon emission computed tomography (SPECT) findings. RESULTS: Ictal onset was uni- or bilateral diffuse with late preponderance over one temporal, or centrotemporoparietal regions. Four patients had preresection intracranial EEG monitoring, which suggested an epileptogenic zone in the posterior temporal and inferior parietal area in two, in the temporal lobe in one, and was inconclusive in the remaining one, who showed late epileptiform activity in the temporal neocortex. A second intracranial implantation was performed in three of them after a first anterior temporal resection. This led to posterior temporal neocortical localization in two and posterior temporal-inferior parietal localization in one. Including subpial transection, these six patients had one to four operations each, but only limited improvement occurred as a result of surgery in this group of individuals. CONCLUSIONS: We conclude that anterior and inferomesial interictal epileptiform temporal discharges and at times even intracranial EEG monitoring may be misleading. Anteromesial temporal resection is ineffective in patients with posterior temporoparietal clinical ictal features.