Biomedical subjects

J M Badier

Publications and source records attributed to J M Badier.

14 recordsLinked to original sources

PubMed2003

Non-supervised spatio-temporal analysis of interictal magnetic spikes: comparison with intracerebral recordings.

OBJECTIVE: Our main goal was to evaluate the accuracy of an original non-supervised spatio-temporal magnetoencephalography (MEG) localization method used to characterize interictal spikes generators. METHODS: MEG and stereotactic intracerebral recordings (stereo-electro-encephalographic exploration, SEEG) data were analyzed independently in 4 patients. MEG localizations were performed with and without anatomical constraints. RESULTS: We analyzed 1326 interictal spikes recorded using MEG. For each patient, 2-3 typical source patterns were described. These source configurations were compared with SEEG. SEEG findings and MEG spatio-temporal localization results were remarkably coherent in our 4 patients. Most of the MEG patterns were similar to interictal SEEG patterns from a spatio-temporal point of view. CONCLUSIONS: We were able to evaluate the usefulness of our non-invasive localization method. This approach described correctly the part of the epileptogenic network involved in the generation of interictal events. Our results demonstrate the potential of MEG in the non-invasive spatio-temporal characterization of generators of interictal spikes.

Adolescent↗

PubMed2001

Intracerebral evoked potentials in pitch perception reveal a functional asymmetry of the human auditory cortex.

One acoustic feature that plays an important role in pitch perception is frequency. Studies on the processing of frequency in the human and animal brain have shown that the auditory cortex is tonotopically organized: low frequencies are represented laterally whereas high frequencies are represented medially. To date, the study of the functional organization of the human auditory cortex in the processing of frequency has been limited to the use of either scalp-recorded auditory evoked potentials (AEPs), which have relatively poor spatial resolving power, or functional imagery techniques, which have poor temporal resolving power. The present study uses intracerebrally recorded AEPs to explore this topic in the primary and secondary auditory cortices of both hemispheres of the human brain. Recordings were carried out in 45 adult patients with drug-resistant partial seizures. In the right hemisphere, clear spectrally organized tonotopic maps were observed with distinct separations between different frequency-processing regions. AEPs for high frequencies were recorded medially, whereas AEPs for low frequencies were recorded laterally. In the left hemisphere, however, this tonotopic organization was less evident, with different regions involved in the processing of a range of frequencies. The hemisphere-related difference in the processing of tonal frequency is discussed in relation to pitch perception.

Acoustic Stimulation↗

PubMed1999

Seizures of temporal lobe epilepsy: identification of subtypes by coherence analysis using stereo-electro-encephalography.

OBJECTIVES: Two subtypes of temporal lobe epilepsy (TLE) according to the structures initially involved during seizures are currently recognized: medial TLE (MTLE) and lateral (or neocortical) TLE (LTLE). A few reports have suggested that the classification of TLE subtypes might be larger according to variations in the interactions between medial structures and the neocortex. In this study, we analyzed these interactions using coherence analysis of stereo-encephalographic (SEEG) signals during spontaneous seizures. METHODS: Twenty-seven patients with drug-resistant TLE, diagnosed from ictal SEEG recordings obtained during pre-surgical evaluation, were studied. Orthogonally implanted depth electrodes with multiple leads according to Talairach's method were used to sample medial and neocortical structures. Coherence analysis of ictal discharges was performed between two SEEG bipolar signals from adjacent leads located either in medial structures (amygdala and hippocampus) or in neocortical regions of the temporal lobe. A new algorithm, which was designed to reduce the bias inherent in coherence estimation, was used to compute the coherence. RESULTS: We were able to classify TLE seizures (TLES) into 4 distinct categories: (1) 'medial' TLES, characterized by medial onset with later involvement of the neocortex in the form of a 'phasic' discharge. High ictal coherence values were observed between medial structures; (2) 'medial-lateral' TLES which started in medial structures with a fast low-voltage discharge (FLVD) which rapidly affects the neocortex (< or = 3 s). High coherence values were observed between medial and lateral structures; (3) 'lateral-medial' TLES, which are different from medial-lateral TLES in that the FLVD starts in the lateral neocortex and involves the amygdala and/or hippocampus almost immediately after; (4) 'lateral' TLES: characterized by a neocortical onset, a delayed involvement of medial structures (when present), and high coherence values between neocortical structures. CONCLUSIONS: These results demonstrate the existence of numerous interactions between medial limbic structures and the neocortex during TLE seizures. Such findings could have implications for surgical strategies and the prognosis of epilepsy surgery, particularly when limited resection is indicated.

Adolescent↗

PubMed1999

Evaluation of a new MEG-EEG spatio-temporal localization approach using a realistic source model.

This paper introduces a new technique for the localization of brain electromagnetic activity: a spatio-temporal fit (SPTF). This algorithm uses some properties of the principal component analysis and makes no assumptions about the number of sources to be located. It was applied to both simulated and real MEG/EEG signals and was compared to the well-known moving dipole fit (MDF) technique. For the simulations, we constructed extended sources, rather than single dipoles, that respected realistic anatomical and temporal properties. From these, we generated, under different noise conditions, MEG and EEG signals from which localization was performed. The real signals were auditory evoked fields. Firstly, it appeared that the SPTF was able to separate simultaneously activated sources even on strongly noisy signals while, most of the time, the MDF failed to give a clear description of the source configuration. Secondly, although we used the same head model to both generate the signals and locate the sources, localization for EEG was inferior to that for MEG. In conclusion, since in all test conditions the SPTF is found to be far superior to MDF, we suggest the use SPTF for the localization of equivalent dipoles.

Algorithms↗

PubMed1999

Time-frequency matching of warped depth-EEG seizure observations.

A methodology of comparing depth-EEG seizure recordings is presented. The approach is based on an extension of Wagner and Fischer's algorithm to N x 2-dimensional sets, allowing a confrontation of nonequal duration observations characterized by their time-frequency distributions. It proceeds by time and frequency warping on the first observation to match the second, under cost constraints. Preliminary results show that relevant signatures can be extracted from recordings.

Algorithms↗

PubMed1998

Anatomical congruence of metabolic and electromagnetic activation signals during a self-paced motor task: a combined PET-MEG study.

We have investigated the degree of spatial correlation between the cerebral blood flow variations measured by positron emission tomography (PET) and the electromagnetic sources as measured by magnetoencephalography (MEG) in five subjects while performing a self-paced right index finger tapping task. Data were processed independently for each technique using both single-case and intersubject analysis. PET and MEG were coregistered with anatomical magnetic resonance images for each subject. Both extension and flexion motor-related fields were extracted from the MEG signal. Using the single dipole model we identified the motor evoked field 1 (MEF1) in all subjects and the motor field (MF) in three subjects. Individual and intersubject averaged PET data showed consistent contralateral primary sensorimotor (PSM) hand area and bilateral supplementary motor area activation. MEG individual and intersubject averaged results demonstrated that both MEF1 and MF dipoles were localized within the PSM PET activated area. Individual PSM mass center to dipole distance was 12 and 15.3 mm on average for the MEF1 and the MF component, respectively. For the same components, the intersubject averaged analysis shows distances between the PET Z-score maximum and the dipole locations of 6.3 and 15.0 mm, respectively. These results show that PET and MEG MEF1 activation signals spatially coincide within instrumental, registration, and modeling errors.

Adult↗

PubMed1997

A method to quantify invariant information in depth-recorded epileptic seizures.

In the field of epilepsy, the analysis of stereoelectroencephalographic (SEEG) signals recorded with depth electrodes provides major information on interactions between brain structures during seizures. A methodology of comparing SEEG seizure recordings is applied in 4 patients suffering from temporal lobe epilepsy. It proceeds in 3 steps: (i) segmentation of SEEG signals, (ii) characterization and labeling of segments and (iii) comparison of observations coded as sequences of symbol vectors. The third step is based on a vectorial extension of Wagner and Fischer's algorithm to first, quantify similarities between observations and second, extract invariant information, referred to as spatio-temporal signatures. These are automatically extracted by the algorithm without the need to make a priori assumptions on the 'patterns' to be searched for. Theoretical results show that two observations of non-equal duration can be matched by deforming the first one (using insertion/deletion operations on vectors) to optimally fit the second, under a minimal cost constraint. Clinical results show that the study brings objective results on reproducible mechanisms occurring during seizures: for a given patient, quantified descriptions of seizure periods are compared and similar ictal patterns, or signatures, are extracted from SEEG signals. Some of these signatures (particularly those containing spikes, spike-and-waves, slow waves and rapid discharges) are relevant: they seem to reflect reproducible propagation schemes whose analysis may help in the understanding of epileptogenic networks.

Electroencephalography↗

PubMed1996

Extraction of spatio-temporal signatures from depth EEG seizure signals based on objective matching in warped vectorial observations.

In the field of epilepsy, the analysis of stereoelectroencephalographic (SEEG) signals recorded with depth electrodes provides major information on interactions between brain structures during seizures. A comprehensive methodology of comparing SEEG seizure recordings is presented. It proceeds in three steps: 1) segmentation of SEEG signals; 2) characterization and labeling of segments; and 3) comparison of observations coded as sequences of symbol vectors. The third step reports a vectorial extension of the Wagner and Fischer's algorithm to first, quantify similarities between observations and second, extract invariant sequences of events, referred to as spatiotemporal signatures. The study shows that two observations of nonequal duration can be matched by deforming the first one to optimally fit the second, under cost constraints. Results show that the methodology allows to exhibit signatures occurring during epileptic seizures and to point out different types of seizure patterns. The study brings objective results on reproducible interactions between brain structures during ictal periods and may help in the understanding of epileptogenic networks.

Algorithms↗

PubMed1995

Spatio-temporal characteristics of paroxysmal interictal events in human temporal lobe epilepsy.

A spatio-temporal mapping technique was applied to stereotactically-implanted depth electrode recordings (SEEG). This technique was used to study the interictal activity in 13 epileptic patients with temporal lobe epilepsies during the pre-surgical evaluation of their epileptogenic zone prior to surgery. The method further provided the precise localization of distinct interictal activities in each explored structure. The high sensitivity of the technique is showed and has demonstrated the evidence of multiple sources during one single sequence of interictal activity. The stability of such an activity was also demonstrated in each patient. A temporal relationship existed between the activity recorded in different structures. Paroxysmal interictal activity thus appeared as an ordered and successive activation of different interictal loci overlapping each other. In this way it was possible to distinguish two different types of activities: primary foci that are activated independently of each other, and secondary foci activated by the primary foci. Finally, in addition to the source localization of interictal activity, the problem of detection and discrimination of the different components must be considered.

Brain Mapping↗

PubMed1994

Evoked potentials recorded from the auditory cortex in man: evaluation and topography of the middle latency components.

The goal of this study is to determine and localize the generators of different components of middle latency auditory evoked potentials (MLAEPs) through intracerebral recording in auditory cortex in man (Heschl's gyrus and planum temporale). The present results show that the generators of components at 30, 50, 60 and 75 msec latency are distributed medio-laterally along Heschl's gyrus. The 30 msec component is generated in the dorso-postero-medial part of Heschl's gyrus (primary area) and the 50 msec component is generated laterally in the primary area. The generators of the later components (60-75 msec) are localized in the lateral part of Heschl's gyrus that forms the secondary areas. The localization of N100 generators is discussed.

Acoustic Stimulation↗

PubMed1991

Localized brain metabolic response correlated with potentials evoked by words.

Evoked potentials (EPs) measure synaptic current flows that propagate from brain to scalp, Alternatively, positron emission tomography (PET) using fluoro-deoxyglucose (FDG) can measure the increased glucose metabolism supporting this synaptic activation. It is difficult to localize the brain activity-generating EPs from their scalp distribution, because activity originating in different regions tends to produce overlapping scalp topographies. In contrast, FDG-PET provides better spatial resolution for activity throughout the brain, but shows only the total metabolism integrated over a 30-min uptake period. We combined the temporal and psychological resolution of EPs with the spatial resolution of PET to help define when and where in the brain words are encoded for meaning.

Adult↗

PubMed1987

[The "epileptogenic zone" in humans: representation of intercritical events by spatio-temporal maps].

In the preoperative investigation of partial epilepsies, electrical characteristics of the so-called epileptogenic area are of critical interest to localize this area. We have always emphasized that the analysis of ictal events themselves, is more valuable than that of inter-ictal anomalis. One reason for this emphasis has been the absence of a reliable method to evaluate the relationship between the topography of ictal and interictal events. An technique for imaging an intracerebral potential field is reported. It allows to analyse the spatio-temporal distribution of interictal events recorded during the SEEG exploration. This technique applied to an illustrative patient shows that the temporo-spatial distribution of interictal spikes is related to that of the ictal discharge itself. A new hypothesis concerning the build up of an epileptogenic area in man is presented.

Adult↗

PubMedDate not supplied

[Cortical mechanisms of auditive perception in man: contribution of cerebral potentials and evoked magnetic fields by auditive stimulations].

The goal of this study is to determine and localize the generators of different components of middle latency auditory evoked potentials (MLAEPs) through intracerebral recordings in auditory cortex in Human (Heschl's gyrus and Planum Temporale). The intracerebral data show that the generators of components at 30, 50, 60 and 75 msec latency are distributed medio-laterally along the Heschl's gyrus. The 30 msec component is generated in the dorso-postero-medial part of the Heschl's gyrus (primary area) and the 50 msec component is generated laterally in the primary area. The generators of the later components (60-75 msec) are localized in the lateral part of the Heschl's gyrus that are the secondary areas. The comparison with the generators of the components of the magnetic auditory evoked field and the tonotopic organization of the auditory cortex are discussed.

Acoustic Stimulation↗

PubMedDate not supplied

Segmentation of depth-EEG seizure signals: method based on a physiological parameter and comparative study.

The analysis of stereoelectroencephalographic (intracerebral recording) signals provides information on the electrical activity of brain structures implied in epileptic seizures. A simple nonparametric adaptive segmentation method, based on a physiologically relevant parameter, is presented and compared with three methods reported in the literature. The comparative frame allows us to objectively test methods for their performances on the same basis. Results show that the proposed method is robust with respect to the types of change studied and easier to conduct, even if it is less accurate about the estimation of instants of change than another method presented in this study. Signals are segmented throughout the duration of seizures without parameter readjustment and generate instants of change in accordance with those interactively delimited by the clinician.

Algorithms↗