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STUDY AIM : To provide a consensus of European leading authorities about the optimal use of clinical neurophysiological (CN) tests (electroencephalogram [EEG]; evoked potentials [EP]; electroneuromyography [ENMG]) in the intensive care unit (ICU) and, particularly, about the way to make these tests clinically useful for the management of individual patients. METHODS : This study gathered together several European clinical neurophysiologists and neurointensivists whose leading contributions in the adult or paediatric ICU and in continuous neuromonitoring had been peer-acknowledged. It was based on both a literature review and each participant's own experience. Given the methodological impossibility to gather studies fulfilling criteria of evidence-based medicine, this article essentially relies on expert opinions that were gained after several rounds, in which each expert was invited to communicate his own contribution to all other experts. A complete consensus has been reached when submitting the manuscript. RESULTS : What the group considered as the best classification systems for EEG and EP abnormalities in the ICU is first presented. CN tests are useful for diagnosis (epilepsy, brain death, and neuromuscular disorders), prognosis (anoxic ischemic encephalopathy, head trauma, and neurologic disturbances of metabolic and toxic origin), and follow-up, in the adult, paediatric, and neonatal ICU. Regarding prognosis, a clear distinction is made between these tests whose abnormalities are indicative of an ominous prognosis and those whose relative normalcy is indicative of a good prognosis. The prognostic significance of any test may vary as a function of coma etiology. CONCLUSION : CN provides quantitative functional assessment of the nervous system. It can be used in sedated or curarized patients. Therefore, it should play a major role in the individual assessment of ICU patients., BUT DE L’ÉTUDE : Présenter l’avis consensuel d’un groupe d’experts européens à propos de l’utilisation optimale de la neurophysiologie clinique (électroencéphalogramme : EEG, potentiels évoqués : PE, électroneuromyographie [ENMG]) en unité de soins intensifs (USI) et, plus particulièrement, de la manière de maximiser l’utilité de ces tests dans la mise au point individuelle des patients. MÉTHODES : Cette étude a rassemblé plusieurs neurophysiologistes cliniciens et neurointensivistes européens dont la compétence en matière de neuroréanimation adulte ou pédiatrique et de neuromonitoring était unanimement reconnue par leurs pairs. Elle est basée à la fois sur une revue de la littérature et sur l’expérience de chaque participant. Vu l’impossibilité, d’ordre méthodologique, de rassembler des études satisfaisant les critères de la médecine factuelle, cet article repose essentiellement sur des opinions d’experts et un consensus atteint au bout de plusieurs « tours de table » lors desquels chaque expert était invité à soumettre sa propre contribution à l’opinion de tous les autres. RÉSULTATS : Nous présentons d’abord ce que le groupe a considéré comme les meilleurs systèmes de classification des anomalies EEG et PE en USI. Les tests neurophysiologiques sont utiles pour le diagnostic (épilepsie, mort cérébrale, anomalies neuromusculaires), le pronostic (encéphalopathies anoxo-ischémiques, traumatismes crâniens, dysfonctionnements neurologiques d’origine métabolique ou toxique) et le suivi, dans les USI adultes, pédiatriques et néonatales. Sur le plan du pronostic, il importe de bien distinguer les tests dont les anomalies sont indicatives d’un mauvais pronostic et ceux qui, lorsqu’ils sont relativement peu perturbés, impliquent un pronostic favorable. Un même test peut avoir une signification pronostique variable en fonction de l’étiologie du coma. CONCLUSION : La neurophysiologie clinique évalue fonctionnellement et quantitativement le système nerveux, même chez les patien

The increasing knowledge about anatomical structures and cellular processes underlying psychiatric disorders may help bridge the gap between clinical manifestations and basic physiological processes. Accordingly, important insights have been brought these last years into a main psychiatric affection, i.e. schizophrenia., Journal Article, Review, SCOPUS: sh.j, info:eu-repo/semantics/published

Etude de la dynamique temporelle de la catégorisation faciale depuis la détection d'un visage dans le champ visuel jusqu'a l'encodage d'une représentation individuelle du visage. Investigation de cette dynamique temporelle via l'électrophysiologie chez le sujet humain (potentiels évoqués). / Temporal dynamics of face visual categorization : an electrophysiological (event-related potentials) approach, (PSY 3) -- UCL, 2007

L'être humain est pourvu des multiples canaux sensoriels par lesquels il appréhende le monde. Un critère fondamental à notre adaptation est notre capacité à établir des relations entre les différentes informations que nos sens perçoivent. Cette capacité est notamment cruciale dans nos interactions sociales puisque nous devons constamment intégrer en une représentation unifiée les informations visuelles (telles que les visages), auditives (telles que les voix) et verbales (telles que le discours ou le nom) afin de pouvoir identifier nos interlocuteurs. Sachant que le traitement des principales informations qui nous permettent d'identifier les personnes (visages, voix et nom de famille) est sous-tendu par l'activation de régions cérébrales spécifiques et distinctes les unes des autres, la question qui se pose est de savoir comment le cerveau opère pour créer une représentation unifiée des personnes que nous connaissons. Dans la première partie de cette thèse, nous passerons en revue différentes études qui ont tenté de cerner les régions cérébrales impliquées dans le traitement (perception et reconnaissance) de chaque type d'information. Le premier chapitre sera consacré aux corrélats cérébraux du traitement des visages, le second à ceux impliqués dans le traitement des noms propres, le troisième à ceux impliqués dans le traitement des voix. Ces processus seront chaque fois abordés sous l'angle de la neuropsychologie cognitive, de l'imagerie cérébrale fonctionnelle et de l'électrophysiologie. Un quatrième chapitre théorique sera consacré à l'étude des processus associatifs entre ces trois types d'informations, et nous verrons que rares sont les études qui ont directement examiné les activités cérébrales spécifiques à la récupération d'associations entre informations relatives à l'identité des personnes. L'approche expérimentale sera abordée dans la seconde partie de cette thèse., Les quatre études décrites dans cette partie se basent sur les résultats de l'étude de Campanella et al. (2001) qui, par PET-scan, ont examiné les régions cérébrales activées par la récupération d'associations entre visages et noms propres. Utilisant la méthode soustractive, consistant en la soustraction de deux conditions unimodales d'une condition bimodale, ces auteurs ont montré une activation d'un réseau d'aires cérébrales latéralisé dans l'hémisphère gauche et incluant notamment le lobule pariétal inférieur, interprété comme étant une région de convergence multimodale où s'opère l'intégration des différentes informations perçues par les sujets. La méthode soustractive sera utilisée dans toutes les expériences décrites dans cette section. La première étude de cette thèse, utilisant la même méthodologie appliquée à la méthode électrophysiologique des potentiels évoqués, aura pour but d'examiner le décours temporel des activités observées par Campanella et al. (2001). La seconde étude en potentiels évoqués aura pour but d'examiner si les activités observées dans les deux études pré-citées sont spécifiques aux processus associatifs entre visages et noms propres, ou s'ils reflètent des processus plus généraux permettant de lier tout objet visuel à son nom. Les études 3 et 4 viseront quant à elles à définir si le lobule pariétal inférieur gauche est impliqué dans l'intégration de stimulations exclusivement visuelles, ou si il est impliqué dans le " binding " de tout type d'information relative aux personnes, quelle que soit les modalités de présentation. Dans ce cadre, l'étude 3 examinera les corrélats cérébraux impliqués dans la récupération d'associations entre visages et voix. L'étude 4 examinera cette question au moyen de l'imagerie par résonance magnétique fonctionnelle. La dernière partie de cette thèse sera consacrée à l'interprétation de l'ensemble des résultats des 4 expériences décrites précédemment. L'accent y sera mis sur la latence d'apparition des ondes, (PSY 3)--UCL, 2006

GOALS: To give an overview on the theoretical and practical applications of chemosensory event-related potentials. METHODS: Chemosensory event-related potentials (ERPs) may be elicited by brief and precisely defined odorous stimuli. Based on the principles of air-dilution olfactometry, a stimulator was developed in the late 1970s, which allows stimulation of the olfactory neuroepithelium and the nasal mucosa with no concomitant mechanical stimulation. Chemosensory ERPs were obtained after stimulation of the olfactory nerve (olfactory ERPs) or the trigeminal nerve (somatosensory or trigeminal ERPs). The characteristics of the stimulator for chemosensory research as well as the variables influencing the responses are discussed in this paper. RESULTS: Implementation and normative data from our department are reported with different clinical examples from otorhinolaryngologic clinic. The bulk of the evoked response consists of a large negative component (often referred to as N1), which occurs between 320 and 450 ms after stimulus onset. This component is followed by a large positive component, often referred to as P2, occurring between 530 and 800 ms after stimulus onset. Absence of olfactory ERPs and presence (even with subtle changes) of somatosensory ERPs is a strong indicator of the presence of an olfactory dysfunction. CONCLUSIONS: This review examines and discusses the methods of chemosensory stimulation as well as the electrophysiological correlates elicited by such stimuli. The clinical applications of chemosensory ERPs in neurology and otorhinolaryngology are outlined.

Numbers convey different meanings when used in different contexts (Wiese, 2003). In a cardinal context, a number will tell us how many entities are in a set and convey quantity meaning. In an ordinal context, a number will refer to the relative position (or rank) of one element within a sequence; non-numerical ordered series (e.g. the letters of the alphabet) can also be used to provide meaningful order information. Because quantity and order are linked up with each other in the cognitive number domain (the larger the quantity a number refers to, the later it is located in the conventional number sequence), the question of whether they rely on some common or distinct underlying mechanism(s) is theoretically relevant and was addressed in the present thesis. Experimental studies showed evidence of both similarities (similar distance and SNARC effects, recruitment of parietal and frontal regions, and conjoint impairment or preservation after brain damage) and dissociations (different developmental course, dissociation after cerebral lesion, and specific behavioural markers) between quantity and order neuro-functional processes. The aim of the present thesis was to clarify the relationship between numerical quantity and order processing and to test the hypothesis that they rely on (at least partially) dissociated mechanisms. We tested this hypothesis in a single case study, an electrophysiological study and in two behavioural experiments. In the neuropsychological study, we reported the case of patient CO, who showed Gerstmann syndrome after bilateral parietal damage and became unable to process sequence order relations (e.g. he couldn't recite the number sequence backwards, nor decide whether a number, letter, day or month comes before or after a given target in the corresponding sequence, and he was unable to verify the order of items in a pair). Nonetheless, the patient had largely preserved quantity processing abilities (he could compare numbers and dot patterns to, (PSY 3)--UCL, 2005

Ecstasy is the common name for a drug mainly containing a substance identified as 3,4-methylenedioxymethamphetamine (MDMA). It has become popular with participants in "raves", because it enhances energy, endurance and sexual arousal, together with the widespread belief that MDMA is a safe drug [Byard, R.W. Gilbert, J. James, R. Lokan, R.J. 1998. Amphetamine derivative fatalities in South Australia. Is "ecstasy" the culprit? Am. J. Forensic Med. Pathol. 19, 261-265]. However, it is suggested that this drug causes a neurotoxicity to the serotonergic system that could lead to permanent physical and cognitive problems. In order to investigate this issue, and during an ERP recording with 32 channels, we used a visual oddball design, in which subjects (14 MDMA abusers and 14 paired normal controls) saw frequent stimuli (neutral faces) while they had to detect as quickly as possible rare stimuli with happy or fearful expression. At a behavioral level, MDMA users imply longer latencies than normal controls to detect rare stimuli. At the neurophysiological level, ERP data suggest as main result that the N200 component, which is involved in attention orienting associated to the detection of stimulus novelty (e.g. [Campanella, S. Gaspard, C. Debatisse, D. Bruyer, R. Crommelinck, M. Guerit, J.M. 2002. Discrimination of emotional facial expression in a visual oddball task: an ERP study. Biol. Psychol. 59, 171-186]), shows shorter latencies for fearful rare stimuli (as compared to happy ones), but only for normal controls. This absence of delay was interpreted as an attentional deficit due to MDMA consumption., Journal Article, Research Support, Non-U.S. Gov't, info:eu-repo/semantics/published

Pain, defined as a percept, is a complex and primarily subjective experience which involves multidimensional sensory, motivational, and cognitive components. The sensory system producing this perception, sometimes referred to as the "nociceptive" system, consists in cutaneous and visceral nociceptors (present in all tissues except the brain), peripheral A[delta]- and C-fiber afferent fibers, and spinal transmission neurons which modulate and project this peripheral input to supraspinal structures such as the brain stem, the thalamus, the limbic system, and the cortex. By selectively and synchronously activating A[delta]- and C-fiber nociceptors, laser heat stimulators have been extensively used to study electrical brain responses involved in nociception. Concomitant activation of A[delta]- and C-fibers produces a dual sensation, composed of first and second pain, but evokes only a single, A[delta]-fiber related, late laser-evoked potential (LEP). Yet, when concomitant activation of A[delta]-fibers is avoided, a C-fiber related ultra-late LEP response is recorded. This well known but poorly understood phenomenon should be taken into account when one infers on the functional significance of the processes these responses reflect. Indeed, the apparent dissociation between perceptual and electrophysiological correlates of A[delta]- and C-nociceptor activation suggests that LEPs reflect cortical processes which are not required for the perception of first or second pain. Study 1. In addition to evoked-potentials, sensory, motor, and cognitive events may induce transient enhancements or attenuations of ongoing EEG oscillations. Hypotheses are that these modulations reflect mechanisms involved in cortical activation, inhibition, and probably binding. However, these electrophysiological responses are cancelled-out by conventional time-averaging procedures. In a first study, novel time-frequency signal-processing methods were developed and applied to the analysis of laser-ind, Thèse de doctorat en sciences biomédicales (neurosciences)(SBIM 3) -- UCL, 2005

An ERP study on 9 healthy participants was carried out to temporally constrain the neural network proposed by Campanella et al. (2001) in a PET study investigating the cerebral areas involved in the retrieval of face-name associations. Three learning sessions served to familiarize the participants with 24 face-name associations grouped in 12 male/female couples. During EEG recording, participants were confronted with four experimental conditions, requiring the retrieval of previously learned couples on the basis of the presentation of name-name (NN), face-face (FF), name-face (NF), or face-name (FN) pairs of stimuli. The main analysis of this experiment consisted in the subtraction of the nonmixed conditions (NN and FF) from the mixed conditions (NF and FN). It revealed two main ERP components: a negative wave peaking at left parieto-occipital sites around 285 ms and its positive counterpart recorded at left centro-frontal electrodes around 300 ms. Moreover, a dipole modeling using three dipoles whose localization corresponded to the three cerebral areas observed in the PET study (left inferior frontal gyrus, left medial frontal gyrus, left inferior parietal lobe) explained more than 90% of the variance of the results. The complementarity between anatomical and neurophysiological techniques allowed us to discuss the temporal course of these cerebral activities and to propose an interactive and original anatomo-temporal model of the retrieval of face-name associations., Clinical Trial, Journal Article, Research Support, Non-U.S. Gov't, FLWIN, info:eu-repo/semantics/published

Pictures from the Ekman and Friesen series were used in an event-related potentials study to define the timing of occurrence of gender differences in the processing of positive (happy) and negative (fear) facial expressions. Ten male and 10 female volunteers were confronted with a visual oddball design, in which they had to detect, as quickly as possible, deviant happy or fearful faces amongst a train of standard stimuli (neutral faces). Behavioral results suggest that men and women detected fearful faces more quickly than happy ones. The main result is that the N2b component, functionally considered as an attentional orienting mechanism, was delayed in men for happy stimuli as compared with fearful ones. Gender differences observed in the processing of emotional stimuli could then originate at the attentional level of the information processing system., Comparative Study, Journal Article, Research Support, Non-U.S. Gov't, info:eu-repo/semantics/published

Several ERP studies have shown an orienting complex, the N2/P3a, associated to the detection of stimulus novelty. Its role consists in preparing the organism to process and react to biologically prepotent stimuli. Whether this N2/P3a: (1) could be obtained with complex visual stimuli, such as with emotional facial expressions; and (2) could take part in a complex discrimination process has yet to be determined. To investigate this issue, event-related potentials were recorded in response to repetitions of a particular facial expression (e.g. sadness) and in response to two different deviant (rare) stimuli, one depicting the same emotion as the frequent stimulus, while the other depicted a different facial expression (e.g. fear). As expected, deviant stimuli evoked an N2/P3a complex of larger amplitude than frequent stimuli. But more interestingly, when the deviant stimulus depicted the same emotion as the frequent stimulus the N2/P3a was delayed compared to the response elicited by the different-emotion deviant. The N2/P3a was thus implicated in the detection of physical facial changes, with a higher sensitivity to changes related to a new different emotional content, perhaps leading to faster adaptive reactions., Journal Article, Research Support, Non-U.S. Gov't, info:eu-repo/semantics/published

Behavioral studies have shown that two different morphed faces perceived as reflecting the same emotional expression are harder to discriminate than two faces considered as two different ones. This advantage of between-categorical differences compared with within-categorical ones is classically referred as the categorical perception effect. The temporal course of this effect on fear and happiness facial expressions has been explored through event-related potentials (ERPs). Three kinds of pairs were presented in a delayed same-different matching task: (1) two different morphed faces perceived as the same emotional expression (within-categorical differences), (2) two other ones reflecting two different emotions (between-categorical differences), and (3) two identical morphed faces (same faces for methodological purpose). Following the second face onset in the pair, the amplitude of the bilateral occipito-temporal negativities (N170) and of the vertex positive potential (P150 or VPP) was reduced for within and same pairs relative to between pairs. This suggests a repetition priming effect. We also observed a modulation of the P3b wave, as the amplitude of the responses for the between pairs was higher than for the within and same pairs. These results indicate that the categorical perception of human facial emotional expressions has a perceptual origin in the bilateral occipito-temporal regions, while typical prior studies found emotion-modulated ERP components considerably later., Journal Article, Research Support, Non-U.S. Gov't, info:eu-repo/semantics/published

Doctorat en sciences psychologiques (PSY 3)--UCL, 2001

Several pathophysiological processes cause reversible functional abnormalities before the appearance of any structural, irreversible damage, in which case the observation of these abnormalities can constitute an invaluable warning signal to prevent the occurrence of irreversible neurological sequelae. Several processes occurring in the operating room (OR) and intensive care unit (lCU) belong to this last category and justify the usefulness of clinical neurophysiology as a neuromonitoring tool during surgery and in coma. Recent technological advances offer new concepts in monitoring of brain signals. In ICU and OR, modern computer technology has recently provided a large number of sophisticated neuromonitoring systems. The dimensions of the helmet vary because it is adjustable. Therefore, the helmet takes into consideration the individual head size and shape. Electrodes for electroencephalography (EEG), stimulus-induced brain oscillations, early somatosensory EPs (SEPs), and brainstem auditory EPs (BAEPs) are generally placed according to the International 10–20 System. Improvement in EEG assessment may be obtained with optimal electrode montages and objective spectral parameters. The montages currently in use are symmetrical and favor central and occipital electrodes. Monitoring of carotid endarterectomy (CEA) is necessary when selective shunting is performed. Monitoring techniques differ in many respects, such as the physiological mechanism studied, the invasiveness of the technique, and subjective versus objective assessment.

Behavioral studies have shown that two different morphed faces belonging to the same identity are harder to discriminate than two faces stemming from two different identities. The temporal course of this categorical perception effect has been explored through event-related potentials. Three kinds of pairs were presented in a matching task: (1) two different morphed faces representing the same identity (within), (2) two other faces representing two different identities (between), and (3) two identical morphed faces (same). Following the second face onset in the pair, the amplitude of the right occipitotemporal negativity (N170) was reduced for within and same pairs as compared with between pairs, suggesting an identity priming effect. We also observed a modulation of the P3b wave, as the amplitude of the responses for within pairs was higher than for between and same pairs, suggesting a higher complexity of the task for within pairs. These results indicate that categorical perception of human faces has a perceptual origin in the right occipitotemporal hemisphere., Journal Article, Research Support, Non-U.S. Gov't, FLWIN, info:eu-repo/semantics/published

(MED - Sciences médicales) -- UCL, 1999

Event-related potentials (ERPs) studies in human subjects have shown inter-individual response variations, probably linked to anatomical and functional brain disparities. The present study was conducted to compare the results obtained by a standard grand-average method and a single subject analysis of VEPs to faces., Clinical Trial, English Abstract, Journal Article, info:eu-repo/semantics/published

In order to investigate stimulus-related and task-related electrophysiological activity relevant for face processing, event-related potentials (ERPs) from 58 electrodes at standard EEG sites were recorded while subjects performed a simple visual discrimination (control) task, in addition to various face processing tasks: recognition of previously learned faces and gender decision on familiar and unfamiliar faces. Three electrophysiological components or dipolar complex were recorded in all subjects: an occipital early component (P1, around 110 ms); a vertex positive potential (VPP; around 158 ms) which appeared to be specific to faces; and a negative central component, N2 (around 230 ms). Parametric analysis and source localization were applied to these components by means of a single-subject analysis methodology. No effect of familiarity was observed on any of these early component. While the VPP appears to be independent of the kind of processing performed, face task modulations of the early P1 and the N2 were observed, with a higher amplitude for the recognition than for the gender discrimination task. An attentional modulation of early visual areas is proposed for the first effect (P1 modulation), while the N2 seems to be related to general visual memory processing. This study strongly suggests that the VPP reflects an early visual stage of face processing in the fusiform gyrus that is strictly stimulus-related and independent of familiarity. It also shows that source localization algorithms may give reliable solutions on single subject averages for early visual components despite high inter-subject variability of the surface characteristics of ERPs., Journal Article, Research Support, Non-U.S. Gov't, info:eu-repo/semantics/published

Objective: To study the event related potentials (ERPs) in coma and altered states of consciousness, their relationship with the clinical status and coma outcome. Methods: ERPs were recorded with a passive auditory oddball paradigm in 103 patients. Their probability of occurrence and the peak latencies and amplitudes were studied as a function of the Glasgow Coma Score (GSC). Their relationship with outcome was studied in a subset of 83 patients examined within the first 4 days, and expressed in terms of sensitivity, specificity, and negative or positive prognostic values. Results: When present, the ERPs to rare stimuli consisted of a fronto-central negativity (N(endog), mean latency: 330 ms) and a fronto-central positivity (P(endog), mean latency: 431 ms) following the exogenous N100-P200 complex. Both their probability of occurrence and their latencies and amplitudes were related with the GCS in anoxic and traumatic comas. The N(endog) and P(endog) had high sensitivity with a negative predictive value of 70% and 100%, respectively, but a low specificity, with a positive predictive value of 44% and 41%, respectively. Conclusions: ERPs can be recorded in some comatose patients and are likely to reflect implicit orienting processes rather than preserved consciousness. Their presence implies a good prognosis but no conclusion can be drawn from their absence., SCOPUS: ar.j, info:eu-repo/semantics/published

This study examines how the recording of the lumbar and subcortical components of the posterior tibial nerve (PTN) SEPs may usefully replace that of cortical components in situations in which these components cannot be reliably obtained (infants, high concentrations of halogenated gasses). Lumbar, brain-stem, and cortical PTN SEPs were intraoperatively monitored in 7 patients undergoing repair of aortic coarctation under variable isoflurane concentration (up to 1.2%). Four patients were less than 1 year old. Two distinct activities were evidenced at the lumbar level in all of the patients: the dorsal root component (DRC) and the dorsal horn negativity (DHN). The equivalent of the adult P30 (lemniscal positivity; LP) was also present in all of the patients, whatever their age or the concentration of isoflurane. By contrast, the parietal activities were absent intraoperatively in the youngest patients. Spinal-cord ischemia consecutive to aortic cross-clamping gave rise to early DHN changes and later alterations of the LP in the two patients in which it occurred, while the DRC and the peripheral nerve activities remained unchanged. This elective sensitivity of the DHN is likely due to it being dependent on the gray matter of the spinal cord, the basal metabolism of which is greater than that of the white matter and to the situation of the DHN generator in a watershed zone of the spinal cord. This study emphasizes the interest of PTN SEPs for spinal-cord monitoring in vascular surgery and the importance of combining the recording of parietal activities with that of the lumbar spinal components.

Guillain-Barré's Syndrome and hearing loss. A child presenting Guillain-Barré's syndrome, together with bilateral hearing loss is presented. The incidence of hypoacusis is unknown. The necessity of behavioural audiometry and electrophysiologic testing is stressed., SCOPUS: ar.j, info:eu-repo/semantics/published

Median nerve somatosensory evoked potentials (SEPs) were recorded in 9 patients undergoing profound hypothermia for surgical repair of the aortic arch. In addition to the known increase in peak latencies, hypothermia gave rise to the appearance of peaks ('P13,' 'N14') inconsistently recognized at normothermia; moreover, profound hypothermia is associated with the disappearance of cortical activities around 20 degrees, of subcortical waves at lower temperatures. The practical implications of the results are 3-fold: firstly, they suggest that the 'P13' and P14 should both be intracranially generated, at a pre- and postsynaptic level with respect to the cuneate nucleus, respectively; secondly, they show that some discrepancies between previous papers dealing with SEPs and hypothermia can be explained by differences in the choice of the reference; thirdly, they bring some suggestions on a better use of SEPs to monitor patients undergoing aortic arch surgery.

L’enregistrement des Potentiels Evoqués (PE), Visuels, Somesthésiques et Auditifs du Tronc Cérébral permet une évaluation des fonctions du cortex et du tronc cérébral et peuvent ainsi fournir des éléments pronostiques déterminants chez les patients comateux. Trois types de facteurs peuvent donner lieu à des altérations des PE chez ces patents : des facteurs extracérébraux (pathologies sensorielles, modifications de la température corporelle, administration de drogues, déprimant l’activité du cerveau), des pathologies à répercussions cérébrales, mais non primitivement cérébrales (insuffisance rénales et hépatiques) et des pathologies primitivement cérébrales (anoxie, hypertension intracrânienne, lésions cérébrales focalisées). Seules les dernières donnent lieu à des altérations influençant réellement le pronostic neurologiques du patient. Deux paramètres essentiels peuvent être extraits des PE : les indices de fonctionnement hémisphérique global et les indices de conduction sous-corticale. Leur caractère normal ou pathologique implique un pronostic favorable ou défavorable si l’examen est pratiqué durant les dix premiers jours ou à partir du premier jour suivant l’accident aigu, respectivement. Les PE présentent un tableau spécifique chez les patients en coma dépassé. Leur enregistrement permet dès lors d’en poser le diagnostic, en complément à l’examen clinique et à l’électroencéphalogramme, même chez les patients chez lesquels ont été administrées des drogues déprimant l’activité du système nerveux. La valeur pronostique des PE dépend, enfin, de leur intégration dans un contexte clinique global, Thèse d'agrégation de l'enseignement supérieur (faculté de médecine) -- UCL, 1990