Showing papers in "Neurophysiologie Clinique-clinical Neurophysiology in 2002"

Estimating the time-course of coherence between single-trial brain signals: an introduction to wavelet coherence.

Abstract: This paper introduces the use of wavelet analysis to follow the temporal variations in the coupling between oscillatory neural signals. Coherence, based on Fourier analysis, has been commonly used as a first approximation to track such coupling under the assumption that neural signals are stationary. Yet, stationary neural processing may be the exception rather than the rule. In this context, the recent application to physical systems of a wavelet-based coherence, which does not depend on the stationarity of the signals, is highly relevant. This paper fully develops the method of wavelet coherence and its statistical properties so that it can be practically applied to continuous neural signals. In realistic simulations, we show that, in contrast to Fourier coherence, wavelet coherence can detect short, significant episodes of coherence between non-stationary neural signals. This method can be directly applied for an ‘online’ quantification of the instantaneous coherence between two signals.

Human alpha oscillations in wakefulness, drowsiness period, and REM sleep: different electroencephalographic phenomena within the alpha band

Abstract: Cortical oscillations in the range of alpha activity (8-13 Hz) are one of the fundamental electrophysiological phenomena of the human electroencephalogram (EEG). Evidence from quantitative EEG data has shown that their electrophysiological features, cortical generation mechanisms, and therefore, their functional correlates vary along the sleep-wake continuum. Specifically, spectral microstructure and EEG coherence levels between anterior and posterior cortical regions permit to differentiate among alpha activity spontaneously appearing in relaxed wakefulness with eyes closed, drowsiness period, and REM sleep, by reflecting distinct properties of neural networks involved in its cortical generation as well as a different interplay between cortical generators, respectively. Besides, the dissimilar spatiotemporal features of brain electrical microstates within the alpha range reveals a different geometry of active neural structures underlying each alpha variant or, simply, changes in the stability level of neural networks during each brain state. Studies reviewed in this paper support the hypothesis that two different alpha variants occur during human REM sleep: 'background responsive alpha activity', blocked over occipital regions when rapid eye movements are present, and 'REM-alpha bursts', non modulated by the alteration of tonic and phasic periods. Altogether, evidence suggests that electrophysiological features of human cortical oscillations in the alpha frequency range vary across different behavioural states, as well as within state, reflecting different cerebral phenomena with probably dissimilar functional meaning.

Epileptic transient detection: wavelets and time-frequency approaches.

Abstract: This paper is aimed at presenting the two main classes of nonstationary signal transforms that are currently used to analyze and to characterize EEG observations. Time-scale methods, or wavelet transforms, allow a time versus duration analysis to be performed whereas time-frequency methods allow spectral contents to be analyzed as a function of time. These two types of transform are well suited to the study of changes either localized or progressive that may be observed in EEG signal dynamics and that sign the evolution of underlying physiological mechanisms. The potential interest of these methods in nonstationary signal representation is illustrated through several academic examples. Then, methods are applied on real EEG signals to solve problems such that the detection of interictal transient signals (like spikes or spike-waves) and the recognition of signatures during ictal periods.

Spike-wave discharge and the microstructure of sleep-wake continuum in idiopathic generalised epilepsy.

Abstract: This review summarises all the evidences about the influence of different vigilance states on the occurrence of spike wave discharge (SWD) in idiopathic generalised epilepsy (IGE) patients. Numerous converging observations showed that full REM-sleep and alert wakefulness exert strong inhibition. A critical zone of vigilance which is a transitional state between waking and non-REM (NREM) sleep, and NREM sleep and REM sleep, has a promoting effect on the absence type spike wave discharge. Spike wave discharges are associated with phasic arousals without awakening and are attached to oscillation son the microstructural level of sleep, perpetuated by cyclic arousal events known as 'cyclic alternating pattern' (CAP), especially within the critical zone, but also along the whole sleep process. More specifically SWD seems to be attached to the 'A-phase' of CAP which is a reactive one and reflects synchronised NREM sleep EEG elements, like K-complexes, spindles and delta groups. The more slow wave elements are found in phase A--like in subtype A1--the more the coincidence with SWD occurs, and the more it is characterised by fast rhythms--as in subtype A2 and A3--the less the association with SWD could be observed. Since subtype A1 is associated with the first sleep cycle and with the descending branches of cycles, it is concluded that SWD appear in those dynamic moments of vigilance level oscillations which were characterised by strong sleep-like answers to arousal influences in high sleep pressure periods of sleep cyclicity. These data harmonize with another line of evidence suggesting that SWD represent the epileptic variant of the complex thalamocortical system function which is the substrate of NREM sleep EEG phenomena. In idiopathic generalised epilepsy there is a growing body of evidence that--as it was assumed by Gloor--spindles transform to SWD pattern. These data explain why those dynamic changes which evoke sleep responses are promoting for the occurrence of SWD. Adapting these data we offer a new interpretation to explain the strong activation effect of sleep deprivation in this kind of epilepsy. We assume that it is mainly due to the forced vigilance level oscillations, especially in morning, when elevated sleep pressure and circadian wake promoting forces, representing opposite tendencies, increase the amount of oscillations.

Eyelid myoclonia with absences: an overlooked epileptic syndrome?

Abstract: Aim: To identify, among patients referred to our Epilepsy Center, those fulfilling eyelid myoclonia with absences (EMA) criteria and to evaluate their semiological, electroclinical and evolutive features. In addition, to examine some possible causes of underdiagnosis and to stress the role of video-EEG (VEEG) recording. Materials and methods: Retrospective analysis of 2780 epileptic patients. Inclusion criteria: Eyelid myoclonia and brief absences, related to EEG generalized paroxysmal activity and triggered by eye closure and/or by intermittent photic stimulation. Results: 7.46% of our patients with idiopathic generalized epilepsy (IGE) could be classified as EMA. Female/male ratio was 1.7:1. Familial history of epilepsy was present in about half of the patients, with two pairs of identical twins in the sample. Rare generalized tonic–clonic seizures occurred in most cases. Conclusions: EMA is a not infrequent condition among IGEs. It is likely to be underdiagnosed due to the subtle clinical semiology and to masking of EEG changes by the effects of age and anti-epileptic drugs. VEEG analysis is often needed for diagnosis of EMA. Most likely, only genetic research will be able to clarify whether EMA is a distinct epileptic syndrome.

Psychophysiological correlates of affects in human olfaction.

Abstract: Pleasantness and arousal have been identified as the main dimensions of affective responses to environment. Pleasantness is defined as the degree of favorable feelings a subject can experience under given circumstances. Arousal is defined as the degree of excitement (general activation) the subject feels under these circumstances. In visual and auditory modalities, many studies using measures such as facial electromyographic (EMG) activity and skin conductance (SC) have found those parameters to vary as a function of either pleasantness or arousal: for example, facial corrugator EMG activity covaries with the pleasantness dimension, while SC increases together with arousal. The first objective of this research is to study the possible covariation between peripheral measures and pleasantness/arousal in olfaction. We also examined the effect of odor intensity on facial and autonomic variations. The second objective was to investigate whether odors could evoke verbally specific emotions (e.g. joy, anger, fear, surprise, disgust or sadness) and also induce specific patterns of peripheral responses. Participants were exposed to 12 different odors while their facial and autonomic parameters were recorded, and estimated their intensity, pleasantness, and arousal capacity. Then, they chose between seven words for emotions (fear, anger, sadness, surprise, neutral, joy or disgust) to describe their reaction to the odor. As in vision, olfactory pleasantness covaries (negatively) with facial activity of the corrugator muscle, and arousal (positively) with skin conductance. No relationships were observed between physiological changes and variations in perceived intensity. Results also showed that emotions of "disgust" and "joy" were more frequently evoked verbally than any other emotions, and that only facial EMG activity distinguishes them (e.g. "disgust" vs. "joy" and "neutral state"). The results are discussed in terms of possible existence of two brain systems (defensive and appetitive), each of them being able to vary in metabolic arousal.

Respective value of pudendal nerve terminal motor latency and anal sphincter electromyography in neurogenic fecal incontinence.

Abstract: Fecal incontinence may be related to a neurogenic injury. Electrodiagnostic tests including pudendal nerve terminal motor latency (PNTML) and external anal sphincter electromyography (AEMG) have been proposed to reveal anal nerve damage. The aim of this study was to assess the respective value of PNTML and AEMG in the diagnosis of fecal incontinence. This study included 80 women (range 23-85 years) with fecal incontinence secondary to obstetrical and/or surgical trauma. They were evaluated by performing PNTML and AEMG. The electrophysiological results were compared and interpreted in the light of anorectal manometry (ARM) results. Electrodiagnostic test abnormalities were found in 64 of 80 patients (80%), including 28 patients with abnormal results for both tests and 36 patients with only one abnormal test. Overall, a neurogenic AEMG pattern was found in 64% of patients and a prolonged PNTML in 51%. No correlation was found between PNTML value and either AEMG grade or ARM parameters, while AEMG grade strongly correlated with squeeze pressure measured by ARM. This study showed that AEMG and PNTML did not give redundant information and allowed to explicit the mechanisms of neurogenic fecal incontinence. We found that AEMG was more sensitive and more closely related to the anal functional status (ARM parameters) than PNTML. These electrodiagnostic tests, particularly AEMG as performed in everyday practice, are useful in the assessment of neurogenic fecal incontinence.

Modulation of visual event-related potentials by emotional olfactory stimuli.

Abstract: The objective of the present study was to determine whether an olfactory prime could modulate behavior and visual event-related potentials (ERPs) obtained in response to a visual stimulation representing female faces. More specifically, we tested the hypothesis that a pleasant odor could have effects on face perception: behavioral effects on subjective emotional estimation of faces, and on associated response times, and electrophysiological effects on the N400 and late positive complex or LPC. Experiments were performed in which subjects had to decide whether the presented face was pleasant or not, while visual ERPs were recorded. Faces were always primed with either a pleasant odor or a neutral olfactory stimulus (pure air). In order to test the effect of subject's awareness, participants were not informed that an odor would be presented in the experimental sessions. Responses were significantly shorter for unpleasant faces. However, no behavioral effects of the pleasant odor on response time or on evaluation of face pleasantness were observed. Late ERPs evoked by faces were modulated by the presence of a pleasant odor, even when subjects were neither warned nor aware of the presence of the odor: in a frontal site and after the diffusion of the odor, the LPC (appearing 550 ms after the presentation of the visual stimulus) evoked by unpleasant faces was significantly more positive than the LPC evoked by pleasant faces. This effect could reflect an enhanced alert reaction to unpleasant faces are preceded by an (incongrous) pleasant odor.

Voluntarily simulated tremor in normal subjects.

Abstract: Based on the hypothesis that rhythmical, tremor-like movements produced by normal subjects might be influenced by similar central oscillatory neuronal networks believed to determine the features of the pathologic tremors of Parkinson's disease (PD) or Essential Tremor (ET) patients, we examined the neurophysiological characteristics of a tremor mimicked by normal volunteers and compare this data with those from PD or ET tremors. Voluntarily simulated tremor (VST) was studied in 47 neurologically intact subjects, resting tremor in 10 patients with PD and postural tremor in 10 patients with ET. Using a tremor analysis system based on a solid state gyroscopic sensor sensitive to angular rate, the following parameters were determined: frequency, amplitude (angular displacement) and regularity (Q coefficient of constancy). We also performed an inertial loading test and a test-retest analysis. Nearly all normal subjects were able to simulate a tremor that was indistinguishable, in frequency and regularity, from that of PD or ET, although the amplitude was significantly higher in normal subjects. As in pathological tremors, the VST frequency was significantly influenced by age, but not by gender, handedness or previous knowledge of tremor. Inertial load did not modify the tremor frequency, suggesting that mechanical factors were minor. We also found a logarithmic inverse relationship between frequency and amplitude of the VST. We concluded that VST shares many similarities with pathological tremors. It is therefore possible that all tremors are somehow influenced by the same central oscillators which may become disinhibited and clinically apparent in pathological conditions such as PD or ET.

Human brain potentials reveal similar processing of non-linguistic abstract structure and linguistic syntactic structure.

Abstract: This research tested the hypothesis that shared or related neurophysiological processes are required for treating (a) non-linguistic abstract structure and (b) some aspects of linguistic syntactic structure. In language, one syntactic structure can be used to create an open class of sentences. We have previously proposed a relation between this generative aspect of syntactic structure and the abstract structure of non-linguistic sequences. For instance, the sequences ‘ABCBAC’ and ‘DEFEDF’ have different serial order or serial structure, but share the same abstract structure ‘123213’. Our recent studies of neuropsychology, simulation and ERPs argued that similar neurophysiological processes are involved in treating non-linguistic abstract structure and certain aspects of linguistic syntactic structure. The current research tests this hypothesis by examining the ERP profile evoked during the processing of non-linguistic sequences vs. sentences. Ten healthy subjects were trained to discriminate between syntactically correct and incorrect sequences and sentences presented visually on a video screen. During the subsequent ERP recording, subjects discriminated between correct and incorrect sequences and sentences presented visually on the screen. This discrimination task yielded, for anomalies in both the abstract and syntactic conditions, a late positivity around 550 ms with partially overlapping topography. These results support our hypothesis that shared or related neurophysiological processes are required for treating non-linguistic abstract structure and aspects of linguistic syntactic structure. However, they also suggest that the overlap between these two types of processing is not complete.

Mutations of the neuronal nicotinic acetylcholine receptors and their association with ADNFLE

Abstract: Elucidating the origin of epileptic seizures represents one of the many ways by which today’s scientists are approaching this devastating neurological disorder. Although epilepsies have several different origins ranging from head trauma to genetically transmissible affections, common neuronal network dysfunction can be recognised between these many forms of the disease. Thus, understanding the basic mechanisms underlying some genetically transmissible epilepsies should bring new and important knowledge that is readily applicable to other types of epilepsies. In this work we review our current knowledge of one genetically transmissible form of nocturnal epilepsy, the ADNFLE. In the light of the most recent findings obtained on five mutants of the neuronal nicotinic acetylcholine receptors associated with ADNFLE, we discuss the effects of these spontaneous genome alterations on the receptor function. The only common trait identified so far between these mutant receptors is an increase in acetylcholine sensitivity. Based on our understanding of the receptor distribution in the different brain areas, their development and the neuronal network circuitry, we hypothesise that increased acetylcholine sensitivity causes an unbalance in the fine tuning of the cortico-reticular thalamic and thalamo-cortical loops. In addition, we illustrate how spontaneous mutations in the gene coding for a receptor provoke a change in its pharmacological profile and thereby might account for the inter-individual therapeutic sensitivity.

Clinical application of laser evoked potentials using the Nd:YAG laser.

Abstract: The clinical interest of a new type of laser evoked potentials (LEPs) using Nd:YAG laser was assessed in the diagnosis of peripheral neuropathies affecting the small-diameter nerve fibres, and of spinal cord lesions, affecting the spinothalamic tract. Twelve patients aged from 26 to 79 years with sensory neuropathies (n = 6) or spinal cord lesions (n = 6) underwent neurophysiological examination of the lower limbs comprising quantitative sensory testing, i.e., the determination of vibratory and thermal thresholds (VT and TT), somatosensory evoked potentials (SEPs) to electrical stimulation and Nd:YAG LEPs. VT and SEPs were used to assess large-diameter afferent nerve fibres and the lemniscal pathways while TT and LEPs were used to assess small-diameter afferent nerve fibres and the spinothalamic tract. In addition, patients with peripheral neuropathy underwent also standard nerve conduction studies to explore large fibres and the recording of sympathetic skin responses (SSRs) to explore small fibres, whereas motor evoked potentials were performed in patients with spinal cord lesion. LEPs were absent bilaterally in all patients with polyneuropathy, even when TT remained within the normal limits and SSRs were present. LEPs were absent after stimulation of the affected limb in all patients with a spinal cord lesion, and allowed to detect subclinical contralateral lesion in two cases. LEPs following Nd:YAG laser stimulation are sensitive in the diagnosis of peripheral and/or central nervous system disorders and they give complementary information as compared to routine electrophysiological tests.

Les activités paroxystiques pseudo-périodiques en électroencéphalographie

Abstract: Periodic and paroxysmal EEG patterns are frequent and easily recognized. They often correlate with particular neurological or systemic conditions. We propose a reclassification and critical examination of these periodic EEG patterns by reviewing the original work presented by J. Gaches in this journal some thirty years ago. Periodic EEG activity is still classified by its localisation--generalised or focal--and by its periodicity--long or short. Periodic long-interval diffuse paroxysmal patterns are reported with rare pathologies such as SSPE, trypanosomiasis or intoxication with phencyclidine. Suppression bursts (SB) may be found in two main situations post-anoxic encephalopathies and drug-induced comas. Ohtahara syndrome is a very rare childhood epileptic syndrome with SB. Periodic short-interval diffuse pattern have been reported in Creutzfeldt-Jakob disease but also in toxic encephalopathies, such as lithium intoxication or as recently reported in acute Cefepime intoxication as well as with metabolic encephalopathies and rarely during AIDS. Periodic lateralized epileptiform discharges (PLEDs) have been classified according to their morphology and the associated condition (epileptic seizures, subtle status, "vascular" seizure). The principal etiology is cerebro-vascular disease and herpes encephalitis but it has also been reported in several other neurological diseases.

An artificial intelligence approach to classify and analyse EEG traces.

Abstract: We present a fully automatic system for the classification and analysis of adult electroencephalograms (EEGs). The system is based on an artificial neural network which classifies the single epochs of trace, and on an Expert System (ES) which studies the time and space correlation among the outputs of the neural network; compiling a final report. On the last 2000 EEGs representing different kinds of alterations according to clinical occurrences, the system was able to produce 80% good or very good final comments and 18% sufficient comments, which represent the documents delivered to the patient. In the remaining 2% the automatic comment needed some modifications prior to be presented to the patient. No clinical false-negative classifications did arise, i.e. no altered traces were classified as 'normal' by the neural network. The analysis method we describe is based on the interpretation of objective measures performed on the trace. It can improve the quality and reliability of the EEG exam and appears useful for the EEG medical reports although it cannot totally substitute the medical doctor who should now read the automatic EEG analysis in light of the patient's history and age.

Metaphorical and non-metaphorical links: a behavioral and ERP study in young and elderly adults

Abstract: Event-related potentials (ERPs) and reaction times were recorded in a semantic decision task with isolated word pairs. The two words in each pair had either a metaphorical semantic link or a non-metaphorical semantic link. The metaphorical semantic link implied familiar expressions. Two conditions without any semantic link were also used, where the two words had a phonological relationship or not. Normal young adults and elderly people participated in this task. Subjects had to decide whether a target word presented 700 ms after a prime word was or was not semantically linked to the prime. Among word pairs with semantic relation, some pairs presented a metaphorical link, and the others presented a non-metaphorical link. Among word pairs without semantic relation, some pairs had a phonological relationship, and the others had no specific relationship. Familiar metaphorical expressions were used. In the two groups, target words elicited larger N400 components when they were related to the prime word by a metaphorical semantic link than when the semantic link was not metaphorical. No significant differences were found between the metaphorical semantic link condition and the two conditions without semantic link. The reaction times analysis showed that young and elderly people took more time to respond to the metaphorical semantic link than to the non-metaphorical semantic link. These results suggest that understanding metaphorical semantic links requires a lexical controlled process and that metaphors have a special status in the semantic memory.

The internal auditory clock: what can evoked potentials reveal about the analysis of temporal sound patterns, and abnormal states of consciousness?

Abstract: Whereas in vision a large amount of information may in theory be extracted from instantaneous images, sound exists only in its temporal extent, and most of its information is contained in the pattern of changes over time. The "echoic memory" is a pre-attentive auditory sensory store in which sounds are apparently retained in full temporal detail for a period of a few seconds. From the long-latency auditory evoked potentials to spectro-temporal modulation of complex harmonic tones, at least two automatic sound analysis processes can be identified whose time constants suggest participation of the echoic memory. When a steady tone changes its pitch or timbre, "change-type" CP1, CN1 and CP2 potentials are maximally recorded near the vertex. These potentials appear to reflect a process concerned with the distribution of sound energy across the frequency spectrum. When, on the other hand, changes occur in the temporal pattern of tones (in which individual pitch changes are occurring at a rate sufficiently rapid for the C-potentials to be refractory), a large mismatch negativity (or MN1) and following positivity (MP2) are generated. The amplitude of these potentials is influenced by the degree of regularity of the pattern, larger responses being generated to a "deviant" tone when the pitch and time of occurrence of the "standards" are fully specified by the preceding pattern. At the sudden cessation of changes, on resumption of a steady pitch, a mismatch response is generated whose latency is determined with high precision (in the order of a few milliseconds) by the anticipated time of the next change, which did not in fact occur. The mismatch process, therefore, functions as spectro-temporal auditory pattern analyser, whose consequences are manifested each time the pattern changes. Since calibration of the passage of time is essential for all conscious and subconscious behaviour, is it possible that some states of unconsciousness may be directly due to disruption of internal "clocks"? Abnormal mismatch potentials may provide a manifestation of a disordered auditory time-sense, sometimes being abolished in comatose patients while the C-potentials and similar responses to the onset of tones are preserved. Both C- and M-potentials were usually found to be preserved, however, in patients who had emerged from coma and were capable of discriminating sounds. Substantially intact responses were also recorded from three patients who were functionally in a "vegetative" state. The C- and M-potentials were once again dissociated in a group of patients with multiple sclerosis, only the mismatch potentials being found to be significantly delayed. This subclinical impairment of a memory-based process responsible for the detection of change in temporal sound patterns may be related to defects in other memory domains such as working memory.

Cognitive effects of precentral cortical stimulation for pain control: an ERP study

Abstract: Electrical stimulation of the motor cortex (MCS) is a promising and increasingly used neurosurgical technique for the control of refractory neuropathic pain. Although its mechanisms of action remain unknown, recent functional imaging data suggest involvement of the thalamus, brainstem and anterior cingulate/orbitofrontal cortex. Since some of these areas are also implicated in higher cognitive functions, notably attentional processes, we analysed cognitive ERPs and behavioural performance during an “oddball” auditory detection task in patients submitted to this procedure. Eleven consecutive patients undergoing MCS because of neuropathic refractory pain, ranging in age from 25 to 71 years, were included in the study. ERPs were obtained in all cases both during the application (“MCS-on”) and within the 10 min that followed discontinuation of the procedure (“MCS-off”). In five patients, ERPs could also be obtained just before the start of MCS. When the patients’ sample was taken as a whole, there were no consistent effects of MCS on the ERPs. There was, however, a significant interaction of MCS action with the patients’ age, reflecting a significant delay during MCS of the cognitive responses N2 and P3 (N200 and P300) in the group of patients older than 50 years exclusively. This effect was rapidly reversible after MCS discontinuation. No MCS-related changes were observed in the N1 component. At the individual level, the effect of MCS on the endogenous ERPs was highly variable, ranging from a total stability of ERPs (mostly in younger subjects) to latency differences of tens of milliseconds in the older group. These results, together with recent experiments showing P300 alteration during repetitive transcranial stimulation, suggest that motor cortex stimulation may interfere with relatively simple cognitive processes such as those underlying target detection, and that the risk of abnormal cognitive effects related to cortical stimulation may increase with age. Although the procedure appears on the whole remarkably safe, complementary neuropsychological studies in this category of patients are advised, as well as caution to possible adverse cognitive effects when using MCS in the elderly, notably in the presence of pre-existent cerebral lesions.

Ajustements posturaux anticipés lors de la flexion du membre supérieur : intérêt du moment de torsion

Abstract: Resume Objectifs : Determiner s’il existe un parametre biomecanique capable de caracteriser les ajustements posturaux dans differentes conditions. Methodes : L’elevation du membre superieur induit chez le sujet debout un moment de torsion vertical Tz mesure par une plate-forme de force. Ce moment a ete etudie chez 10 sujets jeunes grâce au systeme opto-electronique Vicon 370. Les sujets, debout sur une plate-forme de force, flechissaient leur bras droit pour attraper une poignee situee a leur portee devant eux, dans 5 conditions : auto-commandees a 3 vitesses (lente, intermediaire, maximale), declenchee (sur signal sonore), lestee (1 kg au poignet) toutes deux a vitesse maximale. Dans une sixieme condition, le bras etait passivement deplace par un experimentateur. Resultats : Tz comportait une phase negative (c’est-a-dire une rotation anti-horaire) dans toutes les conditions. Elle n’etait precedee d’une phase positive, precedant le debut du mouvement, que lorsque ce dernier etait volontaire. La phase positive de Tz etait retardee dans la condition declenchee (– 60 ms) par rapport a la condition auto-commandee a vitesse maximale (– 155 ms) et n’etait pas modifiee par la charge et la vitesse. Par contre son amplitude augmentait avec la vitesse, la charge et en condition declenchee. Conclusion : Le moment de torsion Tz et notamment sa phase positive permet de mesurer la latence, la duree et l’intensite de la preparation posturale associee a un mouvement volontaire, en fonction des caracteristiques de ce dernier. Il caracterise donc les ajustements posturaux dans toutes les conditions, y compris pour des vitesses faibles.

Étude électromyographique paravertébrale dorso-lombaire: Analyse en mode multi-MUP et établissement de normes au sein d'une population de référence

Abstract: Resume Ce travail vise a etablir des normes pour les parametres electromyographiques de la musculature paravertebrale dorso-lombaire. Materiel et Methodes. 75 sujets sains, asymptomatiques sur le plan rachidien, sont soumis a une etude electromyographique des faisceaux musculaires du multifidus dont l’innervation monosegmentaire depend du rameau posterieur du nerf rachidien. Les myotomes T8 , L3 , L4 , L5 et S1 sont explores. L’activite spontanee de repos et les parametres quantitatifs des potentiels d’unite motrice obtenus par l’analyse en mode multi-MUP (Motor Unit Potential) sont etudies. Resultats et conclusion. Aucun potentiel de fibrillation, aucun potentiel lent de denervation ni aucune fasciculation n’est enregistre au repos. Il n’apparait aucune influence du sexe ou de l’âge sur l’analyse quantitative des potentiels d’unite motrice. Des normes de reference sont etablies pour les niveaux segmentaires T8 et L5 sur le calcul des moyennes des 20 potentiels d’unite motrice isoles chez chaque sujet. Un intervalle de reference est egalement defini a partir des limites extremes inferieure et superieure des valeurs individuelles. Cette etude met a la disposition des electrophysiologistes des valeurs de reference permettant d’objectiver une eventuelle pathologie myogene ou neurogene, en particulier dans le cadres des radiculopathies lombo-sacrees.

Crises giratoires répétitives révélatrices d’une hyperglycémie non cétosique

Abstract: Resume Nous rapportons le cas d’une patiente, sans antecedents particuliers, qui presente brutalement des crises giratoires repetitives. L’EEG montrait un foyer d’ondes lentes paroxystiques centro-parietales droites. Le bilan biologique a mis en evidence une hyperglycemie sans cetose. Les crises ont disparu en 48 heures sous insulinotherapie. La survenue d’une hemiplegie gauche un mois plus tard, secondaire a une ischemie sylvienne, pose le probleme d’une ischemie focale transitoire pouvant expliquer les crises.

Orientation spatiale de l’attention : étude des temps de réaction lors du mouvement de pointage

Abstract: Resume Objectif : L’objectif de ce travail est d’etudier l’influence de l’information prealable au mouvement sur l’orientation spatiale et le controle interne de l’attention chez des sujets adultes normaux. Materiel et Methodes : Le protocole experimental comporte une situation de temps de reaction simple avec un indice oriente et deux situations de temps de reaction de choix : une avec indice preparatoire neutre et une ou existe un indice d’amorcage avec biais de probabilite de compatibilite entre un stimulus preparatoire (S1) et un stimulus imperatif (S2). Les mecanismes de mise en jeu de la vigilance et de l’orientation de l’attention sont etudies en evaluant les effets sur les temps de reaction d’une part du signal preparatoire et d’autre part du biais de probabilite de compatibilite entre S1 et S2. Le signal preparatoire vise a orienter de facon explicite l’attention du sujet vers la position de la cible a pointer, la compatibilite entre S1 et S2 a pour but de mettre en jeu de facon implicite, le controle interne de l’attention du sujet. L’attention du sujet est ainsi sollicitee par l’information prealable a un mouvement de pointage sur une cible visuelle, cette information comportant deux composantes : une composante explicite liee a la position de S1 et une composante implicite liee a la probabilite de compatibilite entre S1 et S2. Resultats et conclusion : Les resultats obtenus chez 16 sujets adultes normaux montrent une amelioration des performances en TR par l’utilisation de la composante explicite de l’information. Nous notons egalement, une prise en compte de la composante implicite de l’information dans les situations de temps de reaction de choix : en effet, il existe un effet d’amorcage qui se traduit par un raccourcissement des temps de reaction indice privilegie compatible par rapport aux temps de reaction indice neutre et une correlation entre les performances en temps de reaction et le degre de compatibilite entre le signal preparatoire et le signal imperatif. Ces resultats suggerent une mise en jeu des differentes composantes du systeme attentionnel dans l’utilisation de l’information prealable au mouvement dans les protocoles de temps de reaction que nous avons utilises. La composante explicite de l’information prealable au mouvement met en jeu la vigilance et l’orientation spatiale de l’attention. Le controle interne de l’attention est mis en jeu par l’utilisation de la composante implicite de l’information.

Study of a patient population investigated for excessive daytime sleepiness (EDS).

Abstract: This study included all patients referred to the out-patient department of our sleep disorders centre from 1993 to 1999 on account of excessive daytime sleepiness (EDS). As a first step, patients in whom a diagnosis was established following appropriate polysomnography were excluded: this included sleep apnea syndrome, increased upper airway resistance syndrome, narcolepsy, periodic movements during sleep or other parasomnia, and epilepsy. Patients regularly taking psychotropic substances or with psychiatric disorders were also excluded. Finally, 128 patients remained in whom no clear diagnosis had been established for EDS, 70 women and 58 men, their ages ranging from 16 to 77 years. They underwent a 48-h recording (night 1-MSLT-night 2-continuous day). The aim of the study was to establish, define and characterise different groups of undiagnosed EDS patients using clinical, electrophysiological and immunological data with the help of hierarchical cluster analysis. Eight groups were characterised: group 1: mild hypersomnia type 1 (n = 11); group 2: hypersomnia frequently associated with HLA type DR2-DQw1 (n = 11); group 3: mild hypersomnia type 2 (n = 28); group 4: morning recovery from disrupted sleep (n = 19); group 5: young "long sleepers with difficulty at waking up" (n = 17); group 6: idiopathic hypersomnia (n = 15); group 7: poor or short sleepers since childhood (n = 8); group 8: older poor sleepers with a late onset of symptoms (n = 19). Characteristic features of these different groups provided consistent and objective arguments leading to a more precise diagnosis for these patients, and helped the initiation of appropriate management and treatment.

Intérêt de la réalisation d’une IRM cérébrale précoce chez le prématuré : corrélation avec l’EEG et le devenir

Abstract: Resume Objectifs : Evaluer l’interet de la realisation d'une IRM cerebrale precoce chez des prematures a risque de sequelles neurologiques et etudier les relations entre les resultats de l’IRM cerebrale, de l'EEG et le devenir. Methodes : Une IRM cerebrale a ete realisee chez 34 prematures d’âge gestationnel moyen corrige de 35,3 SA (29–40SA) et d’âge reel de 5,3 semaines (1–11 semaines). Ils presentaient un comportement neurologique pathologique et/ou 2 EEG anormaux et/ou 2 ETF anormales. Les resultats de l’imagerie ont ete correles a ceux de 3 EEG (enregistres avant 15 j de vie, entre 15 j et un mois de vie et apres le premier mois de vie) et au devenir de chaque enfant. Resultats : Deux correlations significatives ont ete mises en evidence entre : 1) les anomalies de l’EEG tardif et la gravite des lesions objectivees sur l’IRM (sensibilite : 100 %, specificite 60 %), 2) la severite des lesions visualisees a l’IRM et la severite du devenir (sensibilite : 75 %, specificite : 80 %). Il n’y a pas de relation significative entre la gravite du devenir et les anomalies de l’EEG. Conclusion : L’indication de l’IRM precoce est justifiee dans une population ciblee de prematures. Elle apporte des informations essentielles pour le diagnostic des lesions neurologiques et la prise en charge de ces enfants. Couplee a l’EEG, la realisation d’une IRM precoce permet de detecter la grande majorite des enfants qui auront des sequelles neurologiques severes.

Comparaison de l’analyse spectrale et de l’analyse non-linéaire de l’EEG dans les troubles cognitifs

Abstract: Resume Dans cette etude portant sur 25 sujets, deux groupes ont ete constitues en fonction des resultats au MMS et des potentiels evoques cognitifs, comportant respectivement 15 sujets normaux et 10 sujets avec une atteinte cognitive. Il a ete realise une analyse spectrale de l’EEG ainsi qu'une analyse non-lineaire en utilisant la methode de representation des recurrences. L’etude statistique a mis en evidence des differences significatives entre les groupes, aussi bien pour les parametres de l’analyse spectrale (pourcentage de theta, indice spectral) que pour ceux de l’analyse non-lineaire (longueur maximale des diagonales, indice de Shannon et pourcentage de determinisme). Enfin les differentes analyses discriminantes realisees sur les groupes ont donne de meilleurs resultats de classement en utilisant les parametres non-lineaires. Les modifications de ces parametres vont dans le sens de ce qui a ete trouve dans la maladie d’Alzheimer avec la methode de Grassberger et Procaccia, qui mesure la dimension de complexite D2. Elles sont en faveur d’une dynamique de l’EEG plus contrainte et moins complexe associee aux alterations cognitives.

Electrically evoked auditory potentials: comparison between transtympanic promontory and round-window stimulations.

Abstract: Objective: electrically evoked auditory potential (eEAP) techniques have been developed in order to assess electrical excitability of auditory nervous pathways in deaf patients before cochlear implantation. The aim of this study was to compare eEAPs recorded after a transtympanic promontory stimulation with those obtained after a round-window stimulation during a surgical approach. Design: eEAPs were recorded after promontory and round-window stimulation in 10 deaf subjects (i.e. 14 ears) who were candidates for cochlear implantation. Results: eEAPs were successfully recorded in 13 out of 14 (93%) and 11 out of 14 (79%) ears after promontory stimulation and round-window stimulation, respectively. Similar waveforms, latencies, thresholds and eV amplitudes were observed in both cases. Conclusions: both tests provide objective and useful information for the patient selection process before cochlear implantation. Transtympanic stimulation should be preferred in clinical practice as it is less invasive than round-window stimulation and does not require surgical exposure.

Le contrôle moteur: quels outils neurophysiologiques pour l'explorer ?

Abstract: Le mouvement fait appel, aussi bien pour sa préparation que son exécution, à différentes régions cérébrales parmi lesquelles les régions corticales sensorimotrices, le cervelet et les noyaux gris centraux sont les principales. Quels moyens neurophysiologiques avons-nous pour explorer ces différentes structures et plus précisément leur fonction motrice ? L’électroencéphalographie (EEG) détecte l’activité corticale et permet d’étudier des potentiels mais aussi des rythmes. Le rétromoyennage de l’EEG par rapport au début d’un mouvement volontaire permet d’objectiver les potentiels de préparation du mouvement, en fait générés aussi bien par l’aire motrice supplémentaire que l’aire motrice primaire. L’analyse des variations de synchronisation des rythmes mu et beta montre une désynchronisation de ces rythmes avant et pendant le mouvement, suivie d’une synchronisation beta. Cependant seules les modifications précédant le mouvement sont spécifiques du caractère volontaire du mouvement, les autres étant obtenues également lors d’un mouvement passif. Est ainsi mise en évidence l’intrication du sensitif et du moteur et l’intérêt d’étudier l’intégration sensorimotrice en utilisant le « gating » des potentiels évoqués somesthésiques. Ces derniers sont atténués pendant mais également avant le mouvement, traduisant une préparation sensorielle au mouvement. La stimulation magnétique transcranienne, outre l’exploration de la voie corticospinale, permet d’étudier les circuits inhibiteurs intra-corticaux par le biais soit de la période de silence corticale, soit de la méthode de double choc qui explore aussi les circuits excitateurs selon l’intervalle séparant les 2 chocs. Quant à la stimulation répétitive, elle permet d’appréhender la fonction d’une région corticale limitée par les conséquences liées à son inhibition. L’influence des noyaux gris centraux peut se manifester sur certains réflexes comme le réflexe de clignement. Cela nécessite néanmoins des protocoles particuliers étudiant l’habituation (par stimulation répétitive), l’excitabilité (par double stimulation) et surtout le conditionnement par une autre stimulation somesthésique ou auditive. L’électromyographie (EMG) ne sert pas qu’à étudier la fonction musculaire ou moto-neuronale. Elle détecte l’activation musculaire, qu’elle soit anormale (permettant alors l’analyse des mouvements anormaux), ou normale, volontaire, telle qu’elle a été préparée par le cerveau. Il est alors possible d’explorer les ajustements posturaux accompagnant ce mouvement volontaire, mais aussi la fonction de programmation temporelle du cervelet en mesurant la durée des bouffées EMG et le délai de mise en jeu du muscle antagoniste lors d’un mouvement balistique. Tous les outils de la neurophysiologie clinique peuvent contribuer à étudier et donc à mieux comprendre le contrôle moteur.

Caractérisation des relations fonctionnelles entre structures cérébrales : du linéaire au non linéaire

Abstract: Two kinds of methods are available in order to assess the functional relationships between different cerebral structures from the analysis of EEG signals: linear and non-linear methods. In this paper, we describe didactically the methodological bases of signal processing. After recalling the significance of the fundamental parameters of a sine wave: frequency, amplitude and phase, we show, from a first example about an epileptic seizure propagation, how a linear variation between phase and frequency can be interpreted as a small time difference between two EEG channels. This linear method hypothesises that these two signals are respectively the input and the output of a linear system. Then, we point out the limits of this method and we introduce non-linear methods. Among the latter, a recent approach introduces a realistic model of EEG which try to relate signal measured quantities to relations between underlying structures which produce them.