EEG changes induced by meditative practices: State and trait effects in healthy subjects and in patients with epilepsy.

The effect of meditation on brain activity has been the topic of many studies in healthy subjects and in patients suffering from chronic diseases. These effects are either explored during meditation practice (state effects) or as a longer-term result of meditation training during the resting-state (trait). The topic of this article is to first review these findings by focusing on electroencephalography (EEG) changes in healthy subjects with or without experience in meditation. Modifications in EEG baseline rhythms, functional connectivity and advanced nonlinear parameters are discussed in regard to feasibility in clinical applications. Secondly, we provide a state-of-the-art of studies that proposed meditative practices as a complementary therapy in patients with epilepsy, in whom anxiety and depressive symptoms are prevalent. In these studies, the effects of standardized meditation programs including elements of traditional meditation practices such as mindfulness, loving-kindness and compassion are explored both at the level of psychological functioning and on the occurrence of seizures. Lastly, preliminary results are given regarding our ongoing study, the aim of which is to quantify the effects of a mindfulness self-compassion (MSC) practice on interictal and ictal epileptic activity. Feasibility, difficulties, and prospects of this study are discussed.

Predictive factors of postoperative outcome in the elderly after resective epilepsy surgery.

OBJECTIVE: To evaluate the efficiency of resective epilepsy surgery (RES) in patients over 50 years and determine prognostic factors. RESULTS: Over the 147 patients over 50 years (54.9±3.8 years [50-69]) coming from 8 specialized French centres for epilepsy surgery, 72.1%, patients were seizure-free and 91.2% had a good outcome 12 months after RES. Seizure freedom was not associated with the age at surgery or duration of epilepsy. In multivariate analysis, seizure freedom was associated with MRI and neuropathological hippocampal sclerosis (HS) (P=0.009 and P=0.028 respectively), PET hypometabolism (P=0.013), temporal epilepsy (P=0.01). On the contrary, the need for intracranial exploration was associated with a poorer prognosis (P=0.001). Postoperative number of antiepileptic drugs was significantly lower in the seizure-free group (P=0.001). Neurological adverse event rate after surgery was 21.1% and 11.7% of patients had neuropsychological adverse effects overall transient. CONCLUSIONS: RES is effective procedure in the elderly. Even safe it remains at higher risk of complication and population should be carefully selected. Nevertheless, age should not be considered as a limiting factor, especially when good prognostic factors are identified.

HD-EEG for tracking sub-second brain dynamics during cognitive tasks.

This work provides the community with high-density Electroencephalography (HD-EEG, 256 channels) datasets collected during task-free and task-related paradigms. It includes forty-three healthy participants performing visual naming and spelling tasks, visual and auditory naming tasks and a visual working memory task in addition to resting state. The HD-EEG data are furnished in the Brain Imaging Data Structure (BIDS) format. These datasets can be used to (i) track brain networks dynamics and their rapid reconfigurations at sub-second time scale in different conditions, (naming/spelling/rest) and modalities, (auditory/visual) and compare them to each other, (ii) validate several parameters involved in the methods used to estimate cortical brain networks through scalp EEG, such as the open question of optimal number of channels and number of regions of interest and (iii) allow the reproducibility of results obtained so far using HD-EEG. We hope that delivering these datasets will lead to the development of new methods that can be used to estimate brain cortical networks and to better understand the general functioning of the brain during rest and task. Data are freely available from https://openneuro.org .

Clinical and biological assessment of lamotrigine and levetiracetam plasma assays at the Rennes University Hospital.

INTRODUCTION: Requests for lamotrigine and levetiracetam plasma assays have increased significantly since their development in the biological and forensic toxicology laboratory at the University Hospital of Rennes in 2015. The purpose of this study was to evaluate the follow-up of French National Authority for Health (HAS) guidelines for antiepileptic drug assays and the impact of assay results on medical management. METHODS: Two hundred and forty-two assay results of these two antiepileptics for 169 patients hospitalized in different care wards between 2015 and 2018 were retrospectively analyzed. RESULTS: The mean age of the study population was 50.3±25.4 years. Of the 207 assays prescribed for epilepsy, 177 (85.5%) were in line with the 2007 HAS guidelines, namely: 76/177 (42.9%) for therapeutic adjustment in the event of seizure recurrence or aggravation; 45/177 (25.4%) for specific clinical situations; 23/177 (13%) for proven or suspected poor compliance; 23/177 (13%) for suspected overdose; 8/177 (4.5%) following initiation of treatment; and 2/177 (1.1%) for drug interaction management. Thirty of the 207 assays (14.5%) were thus inappropriate. No significant differences were found regarding the hospitalization frequency after a visit to the emergency room (P=0.9) between patients with lamotrigine and/or levetiracetam plasma assays in therapeutic ranges versus those with concentrations outside the therapeutic ranges. Dosage changes were more frequent in patients with assays in therapeutic ranges compared to patients with plasma assays outside the therapeutic ranges (P=0.0015), suggesting a treatment reassessment primarily based on clinical criteria. CONCLUSION: The analysis of requests for antiepileptic drug assays at the University Hospital of Rennes revealed that clinicians were well aware of the HAS guidelines. In addition, the assay results were mainly consistent with clinical intuition, suggesting a real added value for patient management. However, the consequences in terms of changes in medical care seem limited. This assessment illustrates the importance of strengthening the dialogue between pharmacists, biologists and clinicians.

[Epidemiology and associated factors with depression among people suffering from epilepsy: A transversal French study in a tertiary center]. / Épidémiologie et facteurs associés au syndrome dépressif chez les patients suivis au centre hospitalo-universitaire de Rennes pour une épilepsie.

OBJECTIVES: The occurrence of depression in people with epilepsy is almost twice as common as in the general population. Furthermore, depression is the first cause of lower quality of life among those patients. Which is why the main goal of this study was to assess the epidemiology of depression and its associated factors among the patients from the tertiary department of epileptology in Rennes. METHODS/RESULTS: The subjects were included prospectively and consecutively at the moment of their consultation or hospitalisation in the department. Personal data about the socio-economic status and the type of epilepsy was collected. The subjects filled validated self-assessment of depression (NDDIE), anxiety (GAD-7) and quality of life (QOLIE-10). Thanks to the NDDIE, the patients were divided into: "depressed" and "not depressed"; and the two groups were compared with univariate and multivariate models. Of the 322 patients followed-up in the department between the 17th of June and the 9th of September 2016 223 of them were included in the study. According to the NDDIE, 22.6% suffered from depression; according to the GAD-7, 46.4% suffered from anxiety. In the "depressed" group, 82% were not under anti-depressant medication. In the univariate model, depression was associated with: anxiety, suicidal ideations, lower quality of life, vague nervus stimulation treatment, anticonvulsant benzodiazepine medication or psychiatric medication, and last of all bitherapy or polytherapy antiepileptic medication compared to monotherapy. In the multivariate model, depression was significantly related to anxiety (OR: 8.86 [3.00; 26.19] p=0.0001), suicidal ideas (OR: 7.43 [2.93; 18.81] p<0.0001), anticonvulsant benzodiazepine medication (OR: 3.31 [1.16; 9.49] p=0.0255), and lower quality of life (OR: 1.09 [1.02; 1.17] p=0.0087). Generalised epilepsy was a protective factor with uni and multivariate models (OR: 0.34 [0.11; 1.00] p=0.0492). CONCLUSIONS: In the tertiary epileptic department of Rennes, more than 20% of patients with epilepsy suffered from depression during the inclusion period according to the NDDIE. Among those "depressed" subjects, fewer than one out of five seemed to receive proper psychiatric care. Which is why this study highlights the importance of interdisciplinary cooperation between neurologists and psychiatrists in order to aim at better management of epileptic patients as a whole.

Complex patterns of spatially extended generators of epileptic activity: Comparison of source localization methods cMEM and 4-ExSo-MUSIC on high resolution EEG and MEG data.

Electric Source Imaging (ESI) and Magnetic Source Imaging (MSI) of EEG and MEG signals are widely used to determine the origin of interictal epileptic discharges during the pre-surgical evaluation of patients with epilepsy. Epileptic discharges are detectable on EEG/MEG scalp recordings only when associated with a spatially extended cortical generator of several square centimeters, therefore it is essential to assess the ability of source localization methods to recover such spatial extent. In this study we evaluated two source localization methods that have been developed for localizing spatially extended sources using EEG/MEG data: coherent Maximum Entropy on the Mean (cMEM) and 4th order Extended Source Multiple Signal Classification (4-ExSo-MUSIC). In order to propose a fair comparison of the performances of the two methods in MEG versus EEG, this study considered realistic simulations of simultaneous EEG/MEG acquisitions taking into account an equivalent number of channels in EEG (257 electrodes) and MEG (275 sensors), involving a biophysical computational neural mass model of neuronal discharges and realistically shaped head models. cMEM and 4-ExSo-MUSIC were evaluated for their sensitivity to localize complex patterns of epileptic discharges which includes (a) different locations and spatial extents of multiple synchronous sources, and (b) propagation patterns exhibited by epileptic discharges. Performance of the source localization methods was assessed using a detection accuracy index (Area Under receiver operating characteristic Curve, AUC) and a Spatial Dispersion (SD) metric. Finally, we also presented two examples illustrating the performance of cMEM and 4-ExSo-MUSIC on clinical data recorded using high resolution EEG and MEG. When simulating single sources at different locations, both 4-ExSo-MUSIC and cMEM exhibited excellent performance (median AUC significantly larger than 0.8 for EEG and MEG), whereas, only for EEG, 4-ExSo-MUSIC showed significantly larger AUC values than cMEM. On the other hand, cMEM showed significantly lower SD values than 4-ExSo-MUSIC for both EEG and MEG. When assessing the impact of the source spatial extent, both methods provided consistent and reliable detection accuracy for a wide range of source spatial extents (source sizes ranging from 3 to 20cm2 for MEG and 3 to 30cm2 for EEG). For both EEG and MEG, 4-ExSo-MUSIC localized single source of large signal-to-noise ratio better than cMEM. In the presence of two synchronous sources, cMEM was able to distinguish well the two sources (their location and spatial extent), while 4-ExSo-MUSIC only retrieved one of them. cMEM was able to detect the spatio-temporal propagation patterns of two synchronous activities while 4-ExSo-MUSIC favored the strongest source activity. Overall, in the context of localizing sources of epileptic discharges from EEG and MEG data, 4-ExSo-MUSIC and cMEM were found accurately sensitive to the location and spatial extent of the sources, with some complementarities. Therefore, they are both eligible for application on clinical data.

Identification of epileptogenic networks from dense EEG: A model-based study.

Epilepsy is a network disease. Identifying the epileptogenic networks from noninvasive recordings is a challenging issue. In this context, M/EEG source connectivity is a promising tool to identify brain networks with high temporal and spatial resolution. In this paper, we analyze the impact of the two main factors that intervene in EEG source connectivity processing: i) the algorithm used to solve the EEG inverse problem and ii) the method used to measure the functional connectivity. We evaluate three inverse solutions algorithms (dSPM, wMNE and cMEM) and three connectivity measures (r(2), h(2) and MI) on data simulated from a combined biophysical/physiological model able to generate realistic interictal epileptic spikes reflected in scalp EEG. The performance criterion used here is the similarity between the network identified by each of the inverse/connectivity combination and the original network used in the source model. Results show that the choice of the combination has a high impact on the identified network. Results suggest also that nonlinear methods (nonlinear correlation coefficient and mutual information) for measuring the connectivity are more efficient than the linear one (the cross correlation coefficient). The dSPM as inverse solution shows the lowest performance compared to cMEM and wMNE.

Chronic vagus nerve stimulation decreased weight gain, food consumption and sweet craving in adult obese minipigs.

Chronic vagus nerve stimulation (VNS) is known to influence food intake and body weight in animals and humans. The aim of our work was to evaluate the effects of long-term VNS in adult obese minipigs. Eight minipigs were fed ad libitum a Western diet to cause obesity, after which half of the animals were implanted with bilateral vagal electrodes connected to constant current stimulators (2mA, 30Hz, 500-µs pulse, ON 30s, OFF 5min). The other animals were implanted with sham devices. Animals were weighed weekly and their daily consumption was measured. Still 14 weeks after surgery, VNS animals (70.3±3.3kg, P>0.10) did not significantly gain weight compared to sham animals (80.6±8.0kg, P<0.05). Furthermore, food consumption decreased in VNS animals (-18%, P<0.02) compared to sham animals (+1%, P>0.10). When subjected to a three-choice meal test (high-fat vs. high-carbohydrates vs. balanced diet), VNS animals decreased their sweet-food consumption compared to sham animals (P<0.05), and increased their balanced diet consumption in comparison to pre-surgery levels. Our results showed that chronic VNS decreased weight gain, food consumption and sweet craving in adult obese minipigs, which indicates that this therapy might be used to decrease appetite in the context of morbid obesity.

[On the best strategies on the best results for surgery of frontal epilepsy]. / Quelles stratégies pour quels résultats dans la chirurgie des épilepsies partielles frontales?

Frontal lobe epilepsy surgery is the second most common surgery performed for drug-resistant partial epilepsy. We investigated the longitudinal outcome in a cohort of patients investigated since 1990 with SEEG and modern diagnostic techniques. We reviewed 105 patients who underwent surgery between 1990 and 2005 (mean follow-up, six years; range: one to 17 years) and analyzed the year-per-year follow-up according to Engel's classification. Favorable outcome (Class I) was observed for 70% and this result was stable at least five years after surgery. More than 90% of patients with lesion-related epilepsies (focal cortical dysplasia and dysembryoplastic neuroepithelial tumors) became seizure-free. Less than 50% of patients classified as having cryptogenic epilepsy (defined as normal imaging and neuropathology on surgical specimen) had a favorable outcome. Permanent neurological sequelae were subtle and rare, especially after surgery for dysplasia in eloquent cortex (primary motor cortex). Our data indicate that frontal surgery is a successful treatment in patients when electrophysiological and morphological investigations demonstrate a well-defined epileptogenic zone or lesion to be surgically resected. Progress in electrophysiological and brain-imaging techniques will further improve the selection of frontal lobe epilepsy surgery candidates.

[Medicoeconomic assessment of epilepsy surgery in adults with medically intractable partial epilepsy. Three-year outcomes from a multicenter French cohort]. / Evaluation médicoéconomique de la chirurgie des épilepsies partielles pharmacorésistantes de l'adulte. Résultats à trois ans d'une étude prospective multicentrique française.

PURPOSE: To compare resective surgery and medical therapy in a cost-effectiveness analysis in a multicenter cohort of adult patients with partial intractable epilepsy. POPULATION AND METHODS: Adult patients with partial, medically intractable, potentially operable epilepsy were eligible and followed every year over five years. Effectiveness was defined as one year without seizure. The long-term costs and effectiveness were extrapolated over the patients' lifetime with a Markov model. Productivity (indirect costs) and quality of life (QOLIE-31, SEALS) were also assessed. Changes before and after surgery were compared between the two groups. RESULTS: Two hundred and eighty-nine patients were included (119 with surgery, 161 medically treated, six not eligible, three lost to follow-up). One year after surgery, 81% of the patients were seizure-free; at two and three years, this rate was 78%. In the medical group, these rates were 10, 18, and 15%, respectively. The cost of the explorations was euro 8464; including surgery, it was euro 19,700. In the medical group, the average annual direct costs were between 3500 and euro 6000. At two years after surgery, the annual direct cost decreased to euro 2768, at three years, it was euro 1233, predominately antiepileptic drug costs. Surgery became cost-effective between seven and eight years. In the surgical group, all the quality-of-life scores improved at one year after surgery and were stable during the second and third years. CONCLUSION: Surgical therapy was cost-effective at the middle term even though indirect costs were not considered.

Basal ganglia involvement in temporal lobe epilepsy: a functional and morphologic study.

OBJECTIVES: A decrease of [(18)F]fluoro-l-dopa uptake in basal ganglia was recently reported in medically refractory epilepsy. The purpose of this study was to assess the involvement of dopaminergic neurotransmission in refractory temporal lobe epilepsy (TLE) and its relationship to glucose metabolism and morphologic changes. METHODS: Twelve TLE patients were studied using [(18)F]fluorodeoxyglucose PET, [(18)F]fluoro-l-dopa PET, and MRI and compared with healthy control volunteers. Morphologic cerebral changes were assessed using voxel-based morphometry. Student t test statistical maps of functional and morphologic differences between patients and controls were obtained using a general linear model. RESULTS: In TLE patients, [(18)F]fluoro-l-dopa uptake was reduced to the same extent in caudate and putamen in both cerebral hemispheres as well as in the substantia nigra (SN). These dopaminergic functional alterations occurred without any glucose metabolism changes in these areas. The only mild morphologic abnormality was found in striatal regions without any changes in the SN. CONCLUSION: The present study provides support for dopaminergic neurotransmission involvement in temporal lobe epilepsy. The discrepancies between gray matter volume atrophy and the pattern of [(18)F]fluoro-l-dopa suggest that basal ganglia involvement is not related to structural subcortical abnormalities. A functional decrease can be ruled out because there was no change of the glycolytic pathway metabolism in these areas.

Current approaches to the use of generic antiepileptic drugs.

Generic substitution is encouraged as a cost containment strategy for the management of health care resources. However, in epilepsy, the consequences of loss of symptom control are important, and antiepileptic drugs have narrow therapeutic indices. For this reason, generic substitution may be problematic, and certain health authorities have excluded antiepileptic drugs from overall policy recommendations on generic prescribing. The absence of bioequivalence data among generic forms and the relatively broad criteria for bioequivalence with the branded drug allow differences in drug exposure to arise that may be clinically relevant and necessitate monitoring of plasma levels when switching formulations to avoid loss of seizure control or emergence of side effects. Management of these issues carries a significant cost, which should be weighed carefully against the cost savings acquired when purchasing the drug. Both physicians and patients have a right to be informed and approve before pharmacists make a generic substitution or switch between generics.

[Use of generic anti-epilepsy drugs in France: survey of neurologists and review of the literature]. / Utilisation des médicaments génériques des anti-épileptiques en France: résultats d'une enquête auprès des neurologues et revue de la littérature.

INTRODUCTION: The use of generic substitution for antiepileptic drugs is more and more frequent but remains controversial. PURPOSE AND METHODS: This survey aimed to assess physicians' feelings towards effectiveness, tolerability and clinical impact of generic substitution of antiepileptic drugs on their patients. A questionnaire was sent to all French private neurologists and hospital specialists in epilepsy. Their responses were recorded from December 2005 to March 2006. RESULTS: A total of 312 neurologists responded. A few prescribed generic antiepileptic drugs; but a few as well indicated not to switch their prescription. Most of them felt discomfort by generic substitution. One third reported breakthrough seizures or new adverse events after generic substitution and 70p.cent extra phone consultation. DISCUSSION: Neurologists' reluctance with prescribing generic AEDs may be explained by several different facts: no controlled study about the safety and efficacy of generic AEDs as compared with brand name drugs, substitutions by pharmacists without their agreement, lack of medical information about generic AEDs, symbolic dimension of the treatment, and, most of all, the fear of breakthrough seizures in patients good controlled. CONCLUSION: A prospective controlled evaluation of the safety and efficacy of generic substitution in epilepsy needs to be performed.

[Vagal nerve stimulation as a treatment of epilepsy]. / La stimulation du nerf vague dans le traitement de l'épilepsie.

INTRODUCTION: Vagus nerve stimulation (VNS) is a non-pharmacological treatment for drug resistant epilepsy. STATE OF ART: The good efficacy and tolerability of this device is now well established after several controlled studies, and more than 17000 people operated on in different countries. The physiology of VNS is not yet well known, and the potential mechanisms of action are reviewed. VNS seems to be as efficient as a new medication without some of the disadvantages (in case of pregnancy for example). SNV may have a beneficial effect for all kinds of drug-resistant epilepsy. PERSPECTIVES: Better knowledge of the underlying anti-epileptic mechanisms may help to select the better responders to this expensive anti-epileptic tool.

[Evaluation of severity in partial intractable epilepsy]. / Evaluation de la gravité de l'épilepsie partielle pharmaco-résistante.

A large number of factors have to be taken into consideration to evaluate the severity of intractable partial epilepsy. These inter-related factors change with compliance and with the frequency of seizures as well as the psycho-social context. We discuss here the different factors which are directly or indirectly related with epilepsy. In clinical practice, only some of these factors are used as criteria of severity. The only truly effective method of determining the real consequences of epilepsy are quality of life could measurements.

[Indications and risks of neurosurgical techniques for drug-resistant partial epilepsy in adults]. / Indications et risques des techniques neurochirurgicales chez l'adulte pour l'épilepsie partielle pharmaco-résistante.

Many different surgical procedures are performed for medically refractory partial epilepsy. Some surgical therapies are performed to cure the epilepsy (for example unifocal epilepsy), others are palliative procedures. To cure epilepsy, temporal lobectomy is the most common surgical procedure. The different techniques are shortly described, indications and complications are discussed.

[Cost-effectiveness of epilepsy surgery in a cohort of patients with medically intractable partial epilepsy--preliminary results]. / Evaluation médico-économique de la chirurgie des épilepsies partielles pharmaco-résistantes de l'adulte. Etude coût-efficacité--résultats préliminaires.

OBJECTIVE: Patients with medically intractable epilepsy are potential candidates for surgery if the epileptogenic tissue is localized and resectable. Surgical therapy can eliminate seizures but is very expensive. We followed a prospective adult cohort of intractable epileptic patients in order to perform a cost-effectiveness analysis. POPULATION AND METHODS: Adult patients with a suspected partial medically intractable and operable epilepsy were eligible for evaluation, explorations and/or surgery. Clinical and economical data were collected at the inclusion and every 6 months over at least two years. Two patient groups were analyzed: some underwent a surgery, others did not. Clinical data were compared between both groups. As the data collection was not yet complete, we compared the surgery to a continuation of the preoperative medical management in a cost-effectiveness analysis. Direct medical and nonmedical costs were evaluated according to a societal perspective. The effectiveness was defined as one year without seizure. We assessed the incremental cost-effectiveness ratio (ICER) for the first two years after the surgery. We also modeled long-term costs and effectiveness and extrapolated the results over the patients' lifetime with a Markov model. We computed the ICER and performed a sensitivity analysis. Indirect costs were measured in physical units and intangible costs were assessed with quality-of-life measures (QOLIE-31, SEALS). Data were compared before and after surgery. RESULTS: Among the 286 patients included, 119 did not enter in the analysis: 7 were not eligible, 44 not operable, 31 did not present a follow-up, 37 still underwent exams. Finally, 89 underwent a surgical treatment, and 78 were medically treated. Disease was more severe in surgical patients than in medical patients: seizures frequency, depressive disorders and cognitive impairment were greater. One year after the surgery, 83% patients were seizure free. During the year before inclusion and the year after surgery, direct costs were mainly due to hospitalization. During the second year after surgery, the cost of antiepileptic drugs predominated. One additional year without seizure costs 23 531 euro one year after surgery and 9533 euro two years after surgery. In a long-term perspective, the surgery became cost-effective between 7 and 8 years after the surgery. CONCLUSION: Surgical therapy is a cost-effective treatment in a middle-term even without indirect costs consideration.

PET evidence for a role of the basal ganglia in patients with ring chromosome 20 epilepsy.

BACKGROUND: Studies in animal models and epileptic patients have suggested that circuits of the basal ganglia may control epileptic seizures and that striatal dopaminergic transmission plays a key role in seizure interruption. Ring chromosome 20 (r[20]) epilepsy is a very homogenous type of epilepsy and is clinically characterized by long-lasting seizures suggesting a dysfunction in the seizure control system. The hypothesis that these long-lasting seizures are associated with a reduction of striatal dopamine was addressed in the present study in drug-resistant patients with r(20) epilepsy using PET. METHOD: The authors performed [18F]fluoro-l-DOPA PET in 14 patients with r(20) epilepsy and compared uptake constants in the putamen and the caudate with those of 10 controls. In addition, the authors examined the correlation between these constants and the percentage of cells with r(20) mosaicism. RESULTS: [18F]fluoro-l-DOPA uptake was significantly decreased bilaterally in the putamen and in the caudate nucleus of patients. This reduction was equal for both nuclei and was not correlated to the percentage of cells with r(20). CONCLUSION: Striatal dopamine is modulated in r(20) epilepsy; dysfunction of this neurotransmission may impair the mechanisms that interrupt seizures.

Unilateral spatial neglect following right inferior parietal cortectomy.

Research in brain-damaged patients has suggested that the right hemisphere plays a role in unilateral spatial neglect (USN), but provides only limited information for pinpointing the intraparietal localization of the lesions associated with this syndrome. We report a case of unilateral neglect in a patient who underwent a right inferior parietal cortectomy for refractory epilepsy without any macroscopic lesion. We describe the evolution of the neuropsychological disturbances observed at 3 and 24 months after cortectomy. This case illustrates the role played by the inferior parietal lobe and, particularly, the parietal opercule in USN syndrome, and provides strong "experimental" evidence of the special role played by the inferior parietal lobule in the perception processes related to spatial attention.

A methodology for generating normal and pathological brain perfusion SPECT images for evaluation of MRI/SPECT fusion methods: application in epilepsy.

Quantitative evaluation of brain MRI/SPECT fusion methods for normal and in particular pathological datasets is difficult, due to the frequent lack of relevant ground truth. We propose a methodology to generate MRI and SPECT datasets dedicated to the evaluation of MRI/SPECT fusion methods and illustrate the method when dealing with ictal SPECT. The method consists in generating normal or pathological SPECT data perfectly aligned with a high-resolution 3D T1-weighted MRI using realistic Monte Carlo simulations that closely reproduce the response of a SPECT imaging system. Anatomical input data for the SPECT simulations are obtained from this 3D T1-weighted MRI, while functional input data result from an inter-individual analysis of anatomically standardized SPECT data. The method makes it possible to control the 'brain perfusion' function by proposing a theoretical model of brain perfusion from measurements performed on real SPECT images. Our method provides an absolute gold standard for assessing MRI/SPECT registration method accuracy since, by construction, the SPECT data are perfectly registered with the MRI data. The proposed methodology has been applied to create a theoretical model of normal brain perfusion and ictal brain perfusion characteristic of mesial temporal lobe epilepsy. To approach realistic and unbiased perfusion models, real SPECT data were corrected for uniform attenuation, scatter and partial volume effect. An anatomic standardization was used to account for anatomic variability between subjects. Realistic simulations of normal and ictal SPECT deduced from these perfusion models are presented. The comparison of real and simulated SPECT images showed relative differences in regional activity concentration of less than 20% in most anatomical structures, for both normal and ictal data, suggesting realistic models of perfusion distributions for evaluation purposes. Inter-hemispheric asymmetry coefficients measured on simulated data were found within the range of asymmetry coefficients measured on corresponding real data. The features of the proposed approach are compared with those of other methods previously described to obtain datasets appropriate for the assessment of fusion methods.