Measuring the electric field generated in several deep brain structures during Transcranial electrical stimulation in humans in-vivo. In addition, we investigated the effects of TES intensities and montages on the intracerebral EF. Transcranial electrical stimulation (TES) has shown for the last decades promises as a treatment for several neurological and psychiatric disorders. Its efficiency is related to the amount of electric field (EF) magnitude delivered on the target. Very few studies (n=3) estimated the in-vivo intracerebral electric fields in human. They relied mainly on electrocorticographic recordings that require a craniotomy and did not precisely focus on targeting the deep cortical structures which can still lead to some discussion about the TES possibility to reach deep structures. We applied Transcranial alternating current stimulations simultaneously with intracerebral recordings (SEEG) in 7 drug-resistant epileptic patients. Two low intensities were used in 6 patients (0.5 and 1mA) and 15 different montages were used in 1 patient. We calculated the electric field by subtracting voltage measured on contiguous intracerebral contacts. We found EF magnitude up to 0.29, 0.38 and 0.54 V/m respectively in the amygdala, the hippocampus, and the cingulate gyrus. Among 91 montage combinations, the global EF difference in the brain was significant in 65% of cases. We also confirmed experimentally that EF magnitude is proportional to TES intensity. In conclusion, EF at a magnitude which can induces stochastic effects, is achievable in the deep brain structures using low intensities. EF is highly correlated to the stimulation intensity and depends on montages.

We aimed to prospectively assess the anatomical concordance of electric source localizations of interictal discharges with the epileptogenic zone (EZ) estimated by stereo-electroencephalography (SEEG) according to different subgroups: the type of epilepsy, the presence of a structural MRI lesion, the aetiology and the depth of the EZ. In a prospective multicentric observational study, we enrolled 85 consecutive patients undergoing pre-surgical SEEG investigation. Electric source imaging (ESI) was performed before SEEG. Anatomical concordance between ESI and EZ was defined according to 36 predefined sublobar regions. ESI was interpreted blinded to- and subsequently compared with SEEG estimated EZ. 74 patients were finally analyzed. 38 patients had temporal and 36 extra-temporal lobe epilepsy. MRI was positive in 52. 41 patients had malformation of cortical development (MCD), 33 had another or an unknown aetiology. EZ was medial in 27, lateral in 13, and medio-lateral in 34. In the overall cohort, ESI completely or partly localized the EZ in 85%: full concordance in 13 cases and partial concordance in 50 cases. The rate of ESI full concordance with EZ was significantly higher in (i) frontal lobe epilepsy (46%; p = 0.05), (ii) cases of negative MRI (36%; p = 0.01) and (iii) MCD (27%; p = 0.03). We demonstrated that ESI more accurately estimated the EZ in subgroups of patients who are often the most difficult cases in epilepsy surgery: frontal lobe epilepsy, negative MRI and the presence of MCD.

According to a widely held view, the main cortical source of the N170 lies in the fusiform gyrus (FG), whereas the posteriorly located inferior occipital gyrus (IOG) would rather generate earlier face-selective responses. In this study, we asked the following questions: – can we find an intracerebral N170 response in thelateral IOG with similar response properties as the N170 measured onthe scalp OT region in the same patient? – are the SEEG responses in the IOG and the LFG correlated with the scalp N170? Here we report neural responses to upright and inverted faces recorded in a unique patient using multicontact intracerebral electrodes implanted in the right IOG and in the OT sulcus above the right lateral FG (LFG) and 28 scalp electrodes. Simultaneous EEG recordings on the scalp identified the N170 over the right OT scalp region. The latency and amplitude of this scalp N170 were correlated at the single-trial level with the N170 recorded in the lateral IOG, close to the scalp lateral occipital surface. In addition, positive component maximal around the latency of the N170 (a P170) was prominent above the internal LFG, whereas this region typically generates an N170 (or “N200”) over its external/ventral surface. Altogether, these observations provide evidence that the IOG is a major cortical generator of the face-selective scalp N170, qualifying the potential contribution of the FG and questioning a strict serial spatiotemporal organization of the human cortical face network.

tDCS is a widely investigated noninvasive neuromodulation technic in neurological and psychiatric disorders. Some studies demonstrate the effect of tDCS on interictal epileptiform discharges (IED) (Fregni et al., 2006). The objective of our study was to investigate the tDCS effect on IED (frequency of occurrence and amplitudes) in intracerebral structures thanks to SEEG investigation. Two patients with focal drug-resistant epilepsy were included: one medial and one lateral temporal lobe epilepsy. In average, they were implanted with 15 SEEG electrodes. Thanks to the SEEG recordings (5 days), epileptologists localized the irritative zone. The experiment was divided in 3 sessions: 20 min sham, then 20 min tDCS (−1 mA) and finaly 20 min sham. The amplitudes and the number of occurrences were analyzed. The results were compared between the sessions. For the medial temporal lobe study, 64 and 33 IED were detected respectively before and after tDCS. The averaged amplitudes in the hippocampus were respectively 742 ± 422 μV and 152 ± 43 μV correspond to a 20% decrease (P < 0.001; Mann–Whitney U test). For the lateral temporal lobe study, we detected respectively 192 and 165 discharges. The averaged amplitudes in the superior temporal gyrus were respectively 136 ± 55 μV and 117 ± 36 μV correspond to a 14% decrease (P < 0.001; Mann–Whitney U test). In this study, we demonstrated that the cathodal tDCS can reduce the number and the amplitude of epileptic discharges in intracerebral structures. The strength of this study is related to the simultaneous SEEG recordings with non-invasive tDCS and the in-vivo human brain investigation (deep and superficial).

Décrire le sommeil dans l’hippocampe humain, en déterminant par stéréo-électroencéphalographie le profil spectral du signal électrique au cours des stades et des cycles du sommeil. Tous les patients avec une épilepsie focale réfractaire ayant bénéficié d’une implantation d’électrodes intra-hippocampiques au centre hospitalier universitaire de Nancy entre août 2012 et juin 2013 ont été considérés pour analyse du sommeil. Six patients avec des hippocampes explorés dépourvus de caractère pathologique ont été analysés. Durant une nuit, nous avons identifié sur l’électroencéphalogramme de surface synchronisé des périodes continues de sommeil N2, N3 et REM pour deux cycles complets de sommeil. Pour chacune de ces périodes, nous avons réalisé une analyse spectrale du signal hippocampique correspondant. Les stades N2, N3 et REM étaient clairement individualisables selon le profil de la puissance spectrale du signal hippocampique, tout en tenant compte des cycles du sommeil. Pour les stades N3 et REM seulement, la puissance du signal hippocampique était significativement diminuée entre le premier et le second cycle du sommeil. À l’instar du cortex, l’hippocampe humain présente une activité électrique variable selon les stades et les cycles de sommeil. Ce constat pose la question de l’effet du sommeil sur les fonctions cognitives dépendantes de l’hippocampe, en particulier la consolidation mnésique.

Electromagnetic brain source localization consists in the inversion of a forward model based on a limited number of potential measurements. A wide range of methods has been developed to regularize this severely ill-posed problem and to reduce the solution space, imposing spatial smoothness, anatomical constraint or sparsity of the activated source map. This last criteria, based on physiological assumptions stating that in some particular events (e.g., epileptic spikes, evoked potential) few focal area of the brain are simultaneously actives, has gained more and more interest. Bayesian approaches have the ability to provide sparse solutions under adequate parametrization, and bring a convenient framework for the introduction of priors in the form of probabilistic density functions. However the quality of the forward model is rarely questioned while this parameter has undoubtedly a great influence on the solution. Its construction suffers from numerous approximation and uncertainties, even when using realistic numerical models. In addition, it often encodes a coarse sampling of the continuous solution space due to the computational burden its inversion implies. In this work we propose an empirical Bayesian approach to take into account the uncertainties of the forward model by allowing constrained variations around a prior physical model, in the particular context of SEEG measurements. We demonstrate on simulations that the method enhance the accuracy of the source time-course estimation as well as the sparsity of the resulting source map. Results on real signals prove the applicability of the method in real contexts.

Contribution of deep brain sources on scalp EEG is still under debate. It is particularly true for mesial temporal sources which are deep with an infolded geometry. We analyzed simultaneous multi-scale EEG recordings (scalp and intracerebral) to delineate their contribution to scalp EEG. Interictal intracerebral spike networks were classified in 3 distinct categories: solely mesial, mesial as well as neocortical, and solely neocortical. The highest and earliest intracerebral spikes were marked and the corresponding simultaneous intracerebral and scalp electroencephalograms were averaged and characterized. In 7 drug-resistant epileptic patients, 21 intracerebral networks (4048 spikes) were identified. Averaged scalp spikes arising respectively from mesial, mesial plus neocortical and neocortical networks had a 7.1, 36.1 and 10 μV average amplitude. Their scalp electroencephalogram electrical field presented a negativity in the ipsilateral anterior and basal temporal electrodes in all networks and a significant positivity in the fronto-centro-parietal electrodes solely in the mesial plus neocortical and neocortical networks. Topographic consistency test proved the consistency of scalp electroencephalogram maps and hierarchical clustering clearly differentiated them. We have thus shown for the first time that mesial temporal sources (i) contribute to scalp electroencephalogram but (ii) cannot be spontaneously visible (mean SNR: −2.1 dB) on scalp at the single trial level.

The objective of this research is to see whether the estimated conductivities using intracerebral electrical stimulations (IES) in a FEM head model change with different stimulation frequencies. In this study, the estimation of in vivo conductivities, as shown in Fig. 1, was performed by minimizing the relative difference measurement (RDM) equation that compares the distribution of the SEEG (and the EEG) potentials resulted from IES with the distribution of the simulated potentials. The simulated potentials are represented by the generated potentials from a homogenous and isotropic five-compartment FEM head model using a simulated IES source. These five compartments are: scalp, skull, cerebrospinal fluid (CSF), gray matter (GM) and white matter (WM), and their initial conductivities before optimization were set to: 0.33, 0.008, 1.79, 0.33 and 0.14 S/m, respectively. The resulted signals from twelve different bipolar square current stimulations of frequency 55 Hz were considered from about 120 SEEG (and EEG) electrodes. For each stimulation, the main frequency component (55 Hz) and its 1st and 2nd harmonics (110 Hz and 165 Hz) were considered. It is clear from Fig. 2 that the average estimated conductivities and their variances change with the frequency. Moreover, the different values of variances, shown in Fig. 2, can be explained by the difference in the stimulation positions and the signal-to-noise ratio. The introduction of EEG measurements increases the variance certainly because EEG measurements are subjected artefacts of exogenous sources. Even though the variance is large, the trends of the averages are preserved with or without EEG measurements. The results show differences in the estimation of conductivity according to the frequencies and the matters. However, it is necessary to remain careful on interpretation of these preliminary results because a capacitive effect can be generated in the interface between the stimulation electrode and the cerebral mediums even if the frequencies are low.

Objective. -Home polysomnography is being increasingly developed for sleep studies, with various grades of quality. This study aimed to determine the feasibility of affordable, high quality home polysomnographic recordings prescribed for suspected sleep-related neurological disorders.Patients and methods. -We prospectively screened all patients referred to the specialist sleep disorders clinic in Nancy University Hospital between May 2011 and August 2011. Patients were eligible for inclusion if they required polysomnography for the diagnosis of a sleep-related neurological disorder. One-night, polysomnography was performed in each patient's home by a trained steep technician. Financial cost was determined prior to inclusion. A recording was considered as satisfactory if all the following criteria were present: at least, one EEG channel with continuous signal allowing determination of sleep stages and wake during more than 66% of sleep time; at least, one usable respiratory channel (airflow or either band) during more than 66% of sleep time; and usable oximetry during more than 66% of sleep time.Results. -Forty-eight of the 139 screened patients were included. Among the 48 home polysomnography recordings, 35 (72.9%) were satisfactory. Thirteen (27.1%) tracings displayed an unsatisfactory loss of EEG data, including seven (14.6%) tracings with an unsatisfactory loss of respiratory data.Conclusion. -Home polysomnography prescribed for suspected sleep-related neurological disorders is feasible, with affordable costs, whilst maintaining high quality recording. Further studies are needed to measure the real medico-economic impact of promoting outpatient domiciliary explorations for sleep-related neurological disorders. (C) 2014 Elsevier Masson SAS. All rights reserved.

Stereo-electroencephalography (SEEG) is considered as the golden standard for exploring targeted structures during pre-surgical evaluation in drug-resistant partial epilepsy. The depth electrodes, inserted in the brain, consist of several collinear measuring contacts (sensors). Clinical routine analysis of SEEG signals is performed on bipolar montage, providing a focal view of the explored structures, thus eliminating activities of distant sources that propagate through the brain volume. We propose in this paper to exploit the common reference SEEG signals. In this case, the volume propagation information is preserved and electrical source localization (ESL) approaches can be proposed. Current ESL approaches used to localize and estimate the activity of the neural generators are mainly based on surface EEG/MEG signals, but very few studies exist on real SEEG recordings, and the case of equivalent current dipole source localization has not been explored yet in this context. In this study, we investigate the influence of volume conduction model, spatial configuration of SEEG sensors and level of noise on the ESL accuracy, using a realistic simulation setup. Localizations on real SEEG signals recorded during intracerebral electrical stimulations (ICS, known sources) as well as on epileptic interictal spikes are carried out. Our results show that, under certain conditions, a straightforward approach based on an equivalent current dipole model for the source and on simple analytical volume conduction models yields sufficiently precise solutions (below 10 mm) of the localization problem. Thus, electrical source imaging using SEEG signals is a promising tool for distant brain source investigation and might be used as a complement to routine visual interpretations.

Purpose: Electrical potentials from deep epileptic generators such as medial temporal lobe structures (MTL) are known to be invisible on sole visual analysis of scalp EEG. Our aim was to assess observability of medial versus neocortical temporal lobe interictal epileptic generators based on simultnaeous SEEG-EEG recordings. Method: Seven consecutive patients undergoing pre-surgical evaluation of drug resistant temporal lobe epilepsy were selected from a prospective cohort of 28 patients undergoing simultaneous depth and surface EEG since 2009. Among them three were right temporal and four left temporal. Simultaneous SEEG-EEG signals were recorded on the same acquisition system using 128 channels. Intra-cerebral interictal spikes (IIS) were selected from depth EEG signals by epileptologists blinded to EEG. They were characterized and classified as medial, or lateral irritative networks. They were marked with triggers which then serve to average correspond- ing surface EEG segments. Averaged EEG events were finally characterized (3D mapping, duration, amplitude and statistics). Results: In average, nine depth electrodes (112 recordings contacts) and 16 scalp electrodes recorded 684 ' 186 IIS per patient. Overall intra- cerebral IIS analysis identified 21 irritative networks that were classified into three categories: mesial (hippocampal formation and collateral sulcus: M, n = 9), mesial and neocortical (M+NC, n = 5) and pure neocortical (NC, n = 7). 3D scalp amplitude map of IIS showed a negative pole in the basal temporal electrodes for all three intra-cerebral networks and a positive pole on the vertex electrodes only for M+NC and NC networks. Conclusion: Deep medial temporal epileptic generators of IIS are observable on surface EEG after averaging. MTL structures are not closed electrical fields. MTL and neocortical IIS networks have a distinct scalp amplitude map.

The possibility to observe electrical potentials from deep brain sources to surface EEG remains unclear and debated among the neuroscience community. This question is particularly crucial in the temporal lobe epilepsies investigations because they involve complex (mesial and/or lateral) epileptogenic networks. Seven patients undergoing pre-surgical evaluation of drug resistant temporal lobe epilepsy were selected from a prospective series of thirty patients in whom simultaneous EEG-SEEG recordings had been performed since 2009. Interictal intracerebral spikes (IIS) were selected on SEEG signals blinded to EEG signals. These IIS were triggered as temporally known (T0) brain sources, and then EEG signals were automatically averaged according to these T0 markers in order to obtain mean interictal surface spikes (ISS). In mean, 9 SEEG electrodes and 16 surface EEG electrodes were simultaneously used where 684Â ± 186 IIS were selected by patient (total number: 4,787). According to the anatomical distribution of the IIS, 21 foci were defined and classified according to three categories: mesial (9 foci), mesial and neocortical (M + NC, 5 foci) and neocortical part of the temporal lobe (NC, 7 foci). Negative mean interictal surface spikes (ISS) were mainly observed in anterior and basal temporal region. In mean, 8.7 mean EEG signals were validated as an ISS for each IIS network. Amplitude, duration and SNR of each IIS class were: 7.2 μV, 72 ms and 16.5 dB for M class; 36.1 μV, 78.1 ms and 22 dB for M + NC class; 10 μV, 87.1 ms and 17.7 dB for NC class. Mesial brain sources contribute to surface EEG. Contrary to several hypothesis, mesial temporal structures cannot be considered as closed electrical field structures or too depth to contribute. The main problem to observe signals from these deep structures concerns the low signal to noise ratio, which for instance required signal processing to see ISS originated from mesial structures.

Discriminating individual faces requires elaborate and refined perceptual skills call for by few other categories of objects. Yet, the neural basis of individual face coding in the human brain remains unknown. Here we were able to test for behavioral individual discrimination during transient inactivation of a face-selective area of the right inferior occipital gyrus ("occipital face area", OFA) in an epileptic patient implanted with intracerebral depth electrodes (patient KV described in Jonas et al., 2012). During electrical intracerebral stimulations of the rOFA, KV was presented with pairs of identical or slightly different (40%) morphs of unknown faces and was asked to tell if the 2 faces were different. Outside stimulations, she was almost flawless (49/54 trials). However, when stimulating one electrode contact (D5) in the rOFA (movies available), her performance dropped to 0% (0 of 6 trials). She clearly stated that there were no visual distortions that disturbed the task. Face-selective ERPs and gamma-ERSP responses were found at this contact, which was located within the rOFA defined in fMRI. Most importantly, evidence for strong sensitivity to individual faces was found at the contact D5 using fast (6 Hz) periodic visual stimulation of blocks of different or identical individual faces (Rossion & Boremanse, 2011). This effect was observed only at a few contiguous electrode contacts, but of all contacts (27 in the right ventral occipito-temporal cortex), the largest difference between the effect for upright and inverted faces was observed at D5. These findings provide the first evidence of transient impairment of individual face discrimination following electrical intracerebral stimulation, and point to a critical functional role of the right OFA in individual face perception (Schiltz & Rossion, 2006). These observations also support the functional relevance of visual adaptation effects obtained with high-level visual stimuli through fast periodic visual stimulation. Meeting abstract presented at VSS 2013

Face perception is subtended by a large set of areas in the human ventral occipito-temporal cortex. However, the role of these areas and their importance for face recognition remain largely unclear. Here we report a case of transient selective impairment in face recognition (prosopagnosia) induced by focal electrical intracerebral stimulation of the right inferior occipital gyrus. This area presents with typical face-sensitivity as evidenced by functional neuroimaging right occipital face area (OFA). A face-sensitive intracerebral N170 was also recorded in this area, supporting its contribution as a source of the well-known N170 component typically recorded on the scalp. Altogether, these observations indicate that face recognition can be selectively impaired by local disruption of a single face-sensitive area of the network subtending this function, the right OFA.