Studying memory processes at different levels with simultaneous depth and surface EEG recordings

Investigating cognitive brain functions using non-invasive electrophysiology can be challenging due to the particularities of the task-related EEG activity, the depth of the activated brain areas, and the extent of the networks involved. Stereoelectroencephalographic (SEEG) investigations in patients with drug-resistant epilepsy offer an extraordinary opportunity to validate information derived from non-invasive recordings at macro-scales. The SEEG approach can provide brain activity with high spatial specificity during tasks that target specific cognitive processes (e.g., memory). Full validation is possible only when performing simultaneous scalp SEEG recordings, which allows recording signals in the exact same brain state. This is the approach we have taken in 12 subjects performing a visual memory task that requires the recognition of previously viewed objects. The intracranial signals on 965 contact pairs have been compared to 391 simultaneously recorded scalp signals at a regional and whole-brain level, using multivariate pattern analysis. The results show that the task conditions are best captured by intracranial sensors, despite the limited spatial coverage of SEEG electrodes, compared to the whole-brain non-invasive recordings. Applying beamformer source reconstruction or independent component analysis does not result in an improvement of the multivariate task decoding performance using surface sensor data. By analyzing a joint scalp and SEEG dataset, we investigated whether the two types of signals carry complementary information that might improve the machine-learning classifier performance. This joint analysis revealed that the results are driven by the modality exhibiting best individual performance, namely SEEG

Electrical Stimulation for Seizure Induction and Functional Mapping in Stereoelectroencephalography

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Réhabilitation du langage dans l'épilepsie temporale pharmaco-résistante

International audienceLes déficits cognitifs causés par l’épilepsie ont des conséquences personnelles, sociales et occupationnelles durables. Dans le cadre de l’Epilepsie du Lobe Temporal Pharmaco-Résistante (ELTPR), la prise en charge médicale consiste à neutraliser la zone épileptogène par une neurochirurgie. Lorsqu’elle a lieu dans l’hémisphère dominant pour le langage, cette intervention est à risque de majorer les troubles de la mémoire verbale et plus de 60% des patients souffrent d'un déclin langagier. Les troubles d’accès lexical (anomie) sont les plus fréquents. Depuis quelques années, l'idée d'une préhabilitation, c'est-à-dire une réhabilitation avant même la chirurgie, est encouragée. Elle pourrait fournir aux patients une "réserve de compétences" dans laquelle ils pourraient puiser après la chirurgie. Nous avons développé une réhabilitation inspirée des travaux de recherche en aphasiologie. Quatre patients ELTPR ont suivi la réhabilitation en post-opératoire et ont présenté des progrès très encourageants. Quinze patients ont ensuite suivi la procédure en période préopératoire. Malgré le déclin langagier, une partie des bénéfices de cette préhabilitation orthophonique a été conservée en post- opératoire. Des effets sur la plasticité cérébrale ont été retrouvés. Pour répondre à la question d'un réel effet protecteur de la préhabilitation, nous proposons une étude randomisée contrôlée multicentrique à grande échelle

Functional Topography of Auditory Areas Derived From the Combination of Electrophysiological Recordings and Cortical Electrical Stimulation

International audienceThe posterior part of the superior temporal gyrus (STG) has long been known to be a crucial hub for auditory and language processing, at the crossroad of the functionally defined ventral and dorsal pathways. Anatomical studies have shown that this “auditory cortex” is composed of several cytoarchitectonic areas whose limits do not consistently match macro-anatomic landmarks like gyral and sulcal borders. The only method to record and accurately distinguish neuronal activity from the different auditory sub-fields of primary auditory cortex, located in the tip of Heschl and deeply buried in the Sylvian fissure, is to use stereotaxically implanted depth electrodes (Stereo-EEG) for pre-surgical evaluation of patients with epilepsy. In this prospective, we focused on how anatomo-functional delineation in Heschl’s gyrus (HG), Planum Temporale (PT), the posterior part of the STG anterior to HG, the posterior superior temporal sulcus (STS), and the region at the parietal-temporal boundary commonly labeled “SPT” can be achieved using data from electrical cortical stimulation combined with electrophysiological recordings during listening to pure tones and syllables. We show the differences in functional roles between the primary and non-primary auditory areas, in the left and the right hemispheres. We discuss how these findings help understanding the auditory semiology of certain epileptic seizures and, more generally, the neural substrate of hemispheric specialization for language

Frequency Selectivity of Persistent Cortical Oscillatory Responses to Auditory Rhythmic Stimulation

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Electrophysiological technical procedures

International audienceThe reliability of the interpretation of SEEG data depends entirely on the technical quality of the acquisition recording. Digitalization of data and the development of computer technology, over the last 20 years have transformed electrophysiological procedures. Recording equipment must be able to record concomitantly clinical events and brain electrical activity. Recording is carried out during wakefulness and sleep and with use of various activation methods (hyperventilation, intermittent photic stimulation). Intracerebral electrical stimulations (with low and high frequency) and the acquisition of evoked potentials complete the SEEG exploration. This chapter will discuss the characteristics of video-EEG recording equipment, procedures for acquisition and creation of SEEG montages, technical recording and activations, procedures of intracerebral electrical stimulations and the acquisition of evoked potentials

Early onset motor semiology in seizures triggered by cortical stimulation during SEEG

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Contributions of Electrophysiology for Identifying Cortical Language Systems in Patients with Epilepsy

International audienceA crucial element of the surgical treatment of medically refractory epilepsy is to delineate cortical areas that must be spared in order to avoid clinically relevant neurological and neuropsychological deficits post-operatively. For each patient, this typically necessitates determining the language lateralization between hemispheres and language localization within hemisphere. Understanding cortical language systems is complicated by two primary challenges: the extent of the neural tissue involved, and the substantial variability across individuals, especially in pathological populations. We review the contributions made through the study of electrophysiological activity to address these challenges. These contributions are based on the techniques of magnetoencephalography, intracerebral recordings, electrical cortical stimulation, and the electro-video analyses of seizures and their semiology. We highlight why no single modality alone is adequate to identify cortical language systems and suggest avenues for improving current practice

How familiarization and repetition modulate the picture naming network

International audienceA common strategy to reveal the components of the speech production network is to use psycholinguistic manipulations previously tested in behavioral protocols. This often disregards how implementation aspects that are nonessential for interpreting behavior may affect the neural response. We compared the electrophysiological (EEG) signature of two popular picture naming protocols involving either unfamiliar pictures without repetitions or repeated familiar pictures. We observed significant semantic interference effects in behavior but not in the EEG, contrary to some previous findings. Remarkably, the two protocols elicited clearly distinct EEG responses. These were not due to naming latency differences nor did they reflect a homogeneous modulation of amplitude over the trial time-window. The effect of protocol is attributed to the familiarization induced by the first encounter with the materials. Picture naming processes can be substantially modulated by specific protocol requirements controlled by familiarity and, to a much lesser degree, the repetition of materials

Speech and music recruit frequency-specific distributed and overlapping cortical networks

International audienceAbstract To what extent does speech and music processing rely on domain-specific and domain-general neural networks? Using whole-brain intracranial EEG recordings in 18 epilepsy patients listening to natural, continuous speech or music, we investigated the presence of frequency-specific and network-level brain activity. We combined it with a statistical approach in which a clear distinction is made between shared , preferred, and domain- selective neural responses. We show that the majority of focal and network-level neural activity is shared between speech and music processing. Our data also reveal an absence of anatomical regional selectivity. Instead, domain-selective neural responses are restricted to distributed and frequency-specific coherent oscillations, typical of spectral fingerprints. Our work highlights the importance of considering natural stimuli and brain dynamics in their full complexity to map cognitive and brain functions