Probabilistic functional tractography of the human cortex revisited

In patients with pharmaco-resistant focal epilepsies investigated with intracranial electroencephalography (iEEG), direct electrical stimulations of a cortical region induce cortico-cortical evoked potentials (CCEP) in distant cerebral cortex, which properties can be used to infer large scale brain connectivity. In 2013, we proposed a new probabilistic functional tractography methodology to study human brain connectivity. We have now been revisiting this method in the F-TRACT project (f-tract.eu) by developing a large multicenter CCEP database of several thousand stimulation runs performed in several hundred patients, and associated processing tools to create a probabilistic atlas of human cortico-cortical connections. Here, we wish to present a snapshot of the methods and data of F-TRACT using a pool of 213 epilepsy patients, all studied by stereo-encephalography with intracerebral depth electrodes. The CCEPs were processed using an automated pipeline with the following consecutive steps: detection of each stimulation run from stimulation artifacts in raw intracranial EEG (iEEG) files, bad channels detection with a machine learning approach, model-based stimulation artifact correction, robust averaging over stimulation pulses. Effective connectivity between the stimulated and recording areas is then inferred from the properties of the first CCEP component, i.e. onset and peak latency, amplitude, duration and integral of the significant part. Finally, group statistics of CCEP features are implemented for each brain parcel explored by iEEG electrodes. The localization (coordinates, white/gray matter relative positioning) of electrode contacts were obtained from imaging data (anatomical MRI or CT scans before and after electrodes implantation). The iEEG contacts were repositioned in different brain parcellations from the segmentation of patients' anatomical MRI or from templates in the MNI coordinate system. The F-TRACT database using the first pool of 213 patients provided connectivity probability values for 95% of possible intrahemispheric and 56% of interhemispheric connections and CCEP features for 78% of intrahemisheric and 14% of interhemispheric connections. In this report, we show some examples of anatomo-functional connectivity matrices, and associated directional maps. We also indicate how CCEP features, especially latencies, are related to spatial distances, and allow estimating the velocity distribution of neuronal signals at a large scale. Finally, we describe the impact on the estimated connectivity of the stimulation charge and of the contact localization according to the white or gray matter. The most relevant maps for the scientific community are available for download on f-tract. eu (David et al., 2017) and will be regularly updated during the following months with the addition of more data in the F-TRACT database. This will provide an unprecedented knowledge on the dynamical properties of large fiber tracts in human.Peer reviewe

Caractéristiques électro-cliniques des crises épileptiques d'origine temporale à début précoce chez des patients opérés à Rennes entre 1993 et 1998

RENNES1-BU Santé (352382103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Indications and limits of stereoelectroencephalography (SEEG)

International audienceEpilepsy surgery is now an accepted treatment to achieve seizure control in carefully selected patients, both children and adults, suffering from drug-resistant focal epilepsy. Although surgical strategies can often be defined on the basis of non-invasive diagnostic procedures, and despite the recent advances in this field, an increasing number of more complex cases requires invasive EEG (iEEG) to provide precise information on the localization of the epileptogenic zone (EZ), its relationships with eloquent cortex (EC), and the feasibility of a tailored surgical resection. Stereoelectroencephalography (SEEG) is one of the iEEG techniques currently used in the presurgical work-up, and it is well-distinguished from other invasive techniques, such as subdural grids and strips. SEEG depth electrodes enable exploration of deeply located structures and lesions, and of buried cortex, which are not easily assessable by subdural or other iEEG methods. Simultaneous recording of SEEG signals from deep and superficial brain structures allows, when the position of each electrode is precisely determined, delineation of a three-dimensional, spatial and temporal organization of epileptic activities. In the following chapter we discuss some specific indications (temporal or extra-temporal, lesional or non-lesional epilepsies) as well as the limits of the SEEG technique, with respect to some epileptological issues during presurgical evaluation

Confusion, memory disorders, and ophthalmoparesis in a patient with AIDS.

International audienc

Involvement of the basal ganglia in refractory epilepsy: an 18F-fluoro-L-DOPA PET study using 2 methods of analysis.: Involvement of the basal ganglia in refractory epilepsy: an 18F-fluoro-L-DOPA PET study using 2 methods of analysis

Studies in animal models and epileptic patients have led to the suggestion that the basal ganglia (BG) are involved in seizures. PET with 6-18F-L-3,4-fluorodihydroxyphenylalanine (18F-fluoro-L-DOPA) has recently demonstrated a reduction of striatal dopamine uptake in drug-resistant epileptic patients with ring chromosome 20 (r20) using a multiple-time graphical analysis. The aim of the present study was to evaluate the involvement of dopamine in other epileptic syndromes using a multiple-time graphical analysis and the all-brain statistical parametric mapping (SPM) analysis. METHODS: Patients with drug-resistant epilepsy were divided into 3 groups: group 1, with r20 epilepsy (n = 16; mean age +/- SD, 21.5 +/- 5.4 y); group 2, with resistant generalized "absence-like" epilepsy (n = 10; mean age, 32.3 +/- 11.4 y); and group 3, with drug-resistant temporal lobe epilepsy with hippocampal sclerosis (n = 9; mean age, 35.2 +/- 10.3 y). We compared 2 strategies of analysis of the 18F-fluoro-L-DOPA uptake constant (K(i), min(-1)) in BG using a multiple-time graphical analysis using regions of interest (the gold-standard method) and an SPM analysis using a voxel-by-voxel statistical t test to avoid a priori hypotheses in the analysis. Each epileptic group was compared with a group of healthy volunteers (n = 10; mean age, 45.1 +/- 16.5 y). RESULTS: A decrease of the mean K(i) value was observed in the striatum in all groups of patients with both types of analysis. With multiple-time graphical analysis, the reduction was evident using the averaged K(i) values over both hemispheres in each BG. Unilateral decreases in each BG were detected in SPM analysis. A ratio of decrease of 18F-fluoro-L-DOPA uptake was observed in the 3 groups of patients. Only the SPM analysis showed a decrease of 18F-fluoro-L-DOPA uptake ipsilateral to the seizure side in patients with temporal lobe epilepsy. Moreover, the all-brain SPM analysis showed a decrease of 18F-fluoro-L-DOPA uptake in the substantia nigra bilaterally (P < 0.001). CONCLUSION: This result confirms the involvement of dopamine neurotransmission in seizure control related to the type of epileptic syndrome. The difference in epileptic types may depend in part on the seizure frequency

Magnetoencephalographic studies of two cases of diffuse subcortical laminar heterotopia or so-called double cortex.

International audienceTwo cases (a young male and a girl, suffering intractable epilepsy) of diffuse subcortical laminar heterotopia, or so-called double cortex (DC) have been investigated using magnetoencephalography (MEG). MEG confirmed involvement of both cortices (hetero- and normocortex) in the genesis of interictal spikes, and, according to the heterogeneity of DC syndrome, some differences were observed: spike initiation in the normocortex and latter involvement of the heterotopic cortex in the man, and rather a cancellation in both cortices in the girl. In addition, participation of heterotopic cortex in physiological activities could be demonstrated in the man

Automatic bad channel detection in intracranial electroencephalographic recordings using ensemble machine learning

International audienceObjective : Intracranial electroencephalographic (iEEG) recordings contain “bad channels”, which show non-neuronal signals. Here, we developed a new method that automatically detects iEEG bad channels using machine learning of seven signal features.Methods : The features quantified signals’ variance, spatial–temporal correlation and nonlinear properties. Because the number of bad channels is usually much lower than the number of good channels, we implemented an ensemble bagging classifier known to be optimal in terms of stability and predictive accuracy for datasets with imbalanced class distributions. This method was applied on stereo-electroencephalographic (SEEG) signals recording during low frequency stimulations performed in 206 patients from 5 clinical centers.Results : We found that the classification accuracy was extremely good: It increased with the number of subjects used to train the classifier and reached a plateau at 99.77% for 110 subjects. The classification performance was thus not impacted by the multicentric nature of data.Conclusions : The proposed method to automatically detect bad channels demonstrated convincing results and can be envisaged to be used on larger datasets for automatic quality control of iEEG data.Significance : This is the first method proposed to classify bad channels in iEEG and should allow to improve the data selection when reviewing iEEG signals

Focal polymicrogyria in children: Contribution of invasive explorations and epileptogenicity mapping in the surgical decision

International audienceObjective: Report of the contribution of invasive EEG (iEEG) and epileptogenicity mappings (EM) in a pediatric cohort of patients with epilepsy associated with focal polymicrogyria (PMG) and candidates for resective surgery.Method: Retrospective pediatric case series of patients presenting focal PMG-related refractory epilepsy undergoing an invasive exploration (iEEG) at Fondation Rothschild Hospital. We reviewed clinical data, structural MRI, and visual analysis of iEEG recordings. Moreover, time-frequency analysis of SEEG signals with a neuroimaging approach (epileptogenicity maps) was used to support visual analysis.Results: Between 2012 and 2019, eight patients were selected. Five patients were explored with stereoelectroencephalography (SEEG) only, one patient with subdural exploration (SDE) only and two patients first underwent SEEG and then SDE. The mean age at seizure onset was 40.3 months (range 3-120), and the mean age for the iEEG 10.8 years (range 7-15). The epileptogenic zone (EZ) appeared concordant to the PMG lesion in only one case, was larger in three cases, smaller in two cases and different in one case. Four cases were selected for tailored resective surgery and one for total callosotomy. Two patients remained seizure-free at their last follow-up (mean 32.6 months, range 7-98). Epileptogenicity mapping (EM) refined the qualitative analysis, showing in four patients an EZ larger than visually defined.Conclusion: This study is the first pediatric study to analyze the value of iEEG and EM as well as operability in focal PMG-related refractory epilepsy. The results illustrate the complexity of this pathology with variable concordance between the EZ and the lesion and mixed response to surgery