Perrine Bocquillon

Use of swLORETA to localize the cortical sources of target- and distracter-elicited P300 components

OBJECTIVE Cognitive event-related potentials (especially P300) have long been used to explore attentional processes. The aim of this study was to identify the cortical areas involved in P300 generation during a selective attention task. METHODS 128 channel electroencephalograms were recorded in 15 healthy controls performing a three-stimulus visual oddball paradigm, in order to identify distracter- and target-elicited P300 components. For each subject, the P300 sources were localized using standardized weighted low-resolution electromagnetic tomography (swLORETA). One sample and paired T-tests were performed using SPM5®. RESULTS Common sources for both P300 components were observed within a large frontoparietal network, including the frontal eye field and dorsal parietal cortex (i.e. the attentional dorsal frontoparietal network). More inferior parietal areas, prefrontal and cingulate cortices (i.e. the attentional ventral frontoparietal network) were also involved in the generation of target-elicited P300. CONCLUSIONS These results suggest that distracter- and target-elicited P300 are both generated by the dorsal frontoparietal network. Moreover, target processing recruits a specific ventral network. SIGNIFICANCE Our data agree with the literature reports using other methods and should help to improve our knowledge of the cerebral networks underlying attentional processes.

Attention impairment in temporal lobe epilepsy: A neurophysiological approach via analysis of the P300 wave

Purpose: Attention is often impaired in temporal lobe epilepsy (TLE). The P300 wave (an endogenous, event‐related potential) is a correlate of attention which is usually recorded during an “oddball paradigm,” where the subject is instructed to detect an infrequent target stimulus presented amongst frequent, standard stimuli. Modifications of the P300 waves latency and amplitude in TLE have been suggested, but it is still not known whether the source regions also differ. Our hypothesis was that temporal lobe dysfunction would modify the P3 source regions in TLE patients. Methods: A comparative, high density, 128‐channel electroencephalographic analysis of the characteristics of P300 (P3b latency and amplitude) was performed in 10 TLE patients and 10 healthy controls during auditory and visual oddball paradigms. The P3b sources were localized on individual 3D MR images using the LORETA method and intergroup statistical comparisons were performed using SPM2® software. Results: Our main results (in both individual analyses and intergroup comparisons) revealed a reduction in temporal (and more particularly mesiotemporal) sources and, to a lesser extent, frontal sources in TLE patients, compared with controls. Discussion: This reduction may reflect direct, local cortical dysfunction caused by the epileptic focus or more complex interference between epileptic networks and normal attentional pathways. Hum Brain Mapp, 2009.

THE SPATIOTEMPORAL DYNAMICS OF EARLY ATTENTION PROCESSES: A HIGH-RESOLUTION ELECTROENCEPHALOGRAPHIC STUDY OF N2 SUBCOMPONENT SOURCES

The N2 subcomponents of event-related potentials are known to reflect early attentional processes. The anterior N2 may reflect conflict monitoring, whereas the posterior N2 may be involved in target detection. The aim of this study was to identify the brain areas involved in the generation of the N2 subcomponents, in order to define the spatiotemporal dynamics of these attentional processes. We recorded 128-channel electroencephalograms in 15 healthy controls performing a three-stimulus visual oddball task and identified standard-, distracter- and target-elicited N2 components. Individual N2 sources were localized using standardized-weighted-low-resolution-electromagnetic-tomography (swLORETA). Comparative analyses were performed with a non-parametric permutation technique. Common N2 generators were observed in the Brodmann area (BA) 24 of the anterior cingulate cortex (ACC). The posterior cingulate cortex and the central precuneus were more involved in distracter processing, whereas the anterior precuneus and BA 32 of the ACC were target-specific. In accordance with previous demonstration of the frontoparietal cortexs critical role in attentional processes, these new data shed light on the ACCs role in conflict monitoring and its interaction with other median and frontoparietal structures in early attentional processes.

Effects of Stimulus-Driven and Goal-Directed Attention on Prepulse Inhibition of Brain Oscillations

Objective: Prepulse inhibition (PPI) is an operational measure of sensory gating. PPI of cortical response to a startling pulse is known to be modulated by attention. With a time-frequency analysis, we sought to determine whether goal-directed and stimulus-driven attention differentially modulate inhibition of cortical oscillations elicited by a startling pulse. Methods: An electroencephalogram (EEG) was recorded in 26 healthy controls performing an active acoustic PPI paradigm. Startling stimuli were presented alone or either 400 or 1000 ms after one of three types of visual prepulse: to-be-attended (goal-directed attention), unexpected (stimulus-driven attention) or to-be-ignored (non-focused attention). We calculated the percentage PPI for the auditory event-related spectral perturbation (ERSP) of theta (4–7 Hz), alpha (8–12 Hz), beta1 (13–20 Hz) and beta2 (20–30 Hz) oscillations and changes in inter-trial coherence (ITC), a measure of phase synchronization of electroencephalographic activity. Results: At 400 ms: (i) PPI of the ERSP of alpha, theta and beta1 oscillation was greater after an unexpected and a to-be-attended prepulse than after a to-be-ignored prepulse; and (ii) PPI of beta2 oscillations was greater after a to-be-attended than a to-be-ignored prepulse. At 1000 ms: (i) PPI of alpha oscillations was greater after an unexpected and a to-be-attended prepulse than after a to-be-ignored prepulse; and (ii) PPI of beta1 oscillations was greater after a to-be-attended than a to-be-ignored prepulse. The ITC values did not vary according to the type of prepulse. Conclusions: In an active PPI paradigm, stimulus-driven and goal-directed attention each have differential effects on the modulation of cortical oscillations.

P8.8 Role of basal ganglia circuits in selective attention: a swLORETA P300 study

P. Bocquillon1, J.-L. Bourriez2, E. Palmero-Soler3, A. Destee4, L. Defebvre5, P. Derambure1, K. Dujardin5 1Université Lille Nord de France, UDSL, Lab. Neurosciences Fonctionnelles et Pathologies, CNRS, FRE 3291, Clinical Neurophysiology Department, Lille University Medical Center, Lille, France, 2Lab. Neurosciences Fonctionnelles et Pathologies, CNRS, FRE 3291, Clinical Neurophysiology Department, Lille University Medical Center, Lille, France, 3Eemagine Medical Imaging Solutions GmbH, Berlin, Germany, 4Université Lille Nord de France, UDSL, Neurology and Movement Disorders Department, Lille University Medical Center, Lille, France, 5Université Lille Nord de France, UDSL, Lab. Neurosciences Fonctionnelles et Pathologies, CNRS, FRE 3291, Neurology and Movement Disorders Department, Lille University Medical Center, Lille, France

Impaired Early Attentional Processes in Parkinson’s Disease: A High-Resolution Event-Related Potentials Study

Introduction The selection of task-relevant information requires both the focalization of attention on the task and resistance to interference from irrelevant stimuli. A previous study using the P3 component of the event-related potentials suggested that a reduced ability to resist interference could be responsible for attention disorders at early stages of Parkinson’s disease (PD), with a possible role of the dorsolateral prefrontal cortex (DLPFC). Methods Our objective was to better determine the origin of this impairment, by studying an earlier ERP component, the N2, and its subcomponents, as they reflect early inhibition processes and as they are known to have sources in the anterior cingulate cortex (ACC), which is involved together with the DLPFC in inhibition processes. Fifteen early-stage PD patients and 15 healthy controls (HCs) performed a three-stimulus visual oddball paradigm, consisting in detecting target inputs amongst standard stimuli, while resisting interference from distracter ones. A 128-channel electroencephalogram was recorded during this task and the generators of the N2 subcomponents were identified using standardized weighted low-resolution electromagnetic tomography (swLORETA). Results PD patients displayed fewer N2 generators than HCs in both the DLPFC and the ACC, for all types of stimuli. In contrast to controls, PD patients did not show any differences between their generators for different N2 subcomponents. Conclusion Our data suggest that impaired inhibition in PD results from dysfunction of the DLPFC and the ACC during the early stages of attentional processes.

The spatiotemporal dynamics of incomplete object recognition

and frequency domain parameteres were analyzed. Variables were analyzed using the SPSS program. Results.— CSR showed statistically significant differences (p%3C0.05) between PD patients and healthy subjects (lower responses and lack of them) and HRV pointed to significantly lower values in patients both in time and frequency-domain when compared with controls. Patients treated with L-DOPA showed a significant less pronounced decrease in all these values. Conclusions.— Patients with PD showed earlier than expected sympathetic and parasympathetic impairments even before clinical manifestations. Such impairment worsened as the disease evolved and was correlated with Hoehn %26 Yahr stage. Treatment with L-DOPA had a stabilizing effect of the autonomic function (more significant in parasympathetic). CSR and HRV are two harmless and simple tools for the early detection of ANS impairment in PD.

P156 Attention impairment in temporal lobe epilepsy: neurophysiological approach by the study of the P300 wave

Purpose: To study different F wave and other neurography parameters in patients with one year following stroke on the hemiparetic and non-paretic side Method: We studied 25 patients (11 men and 14 women) aged 21 to 75 years one year following stroke. 19 patients had a hemispheric infarction and 6 patients a brainstem infarction. The patients were studied bilaterally. The ulnar, peroneal and tibial nerve motor neurography and F waves were studied. The following parameters were measured: number of F waves/20 stimuli, F minimum latency, F wave dispersion, distal latency, M amplitude and motor conduction velocities. The amplitude of F waves was not analyzed in this study because the equipment used did not include this parameter. The sural nerve sensory conduction velocity and sensory nerve response amplitude were also measured. Results: The hemiparetic and unaffected sides were compared with each other using paired-samples t-test. The only significant side difference seen was in the ulnar nerve minimum F wave latency, which was shorter on the paretic side. There were no systematic side differences seen consistently in all three motor nerves. The slight difference in the ulnar nerve is probably by chance. Conclusion: There are no systematic side differences in the analyzed F wave parameters, motor conduction velocities, M amplitude and distal latency one year following stroke on the unaffected and hemiparetic side.

A - 21 Étude des troubles attentionnels dans l’épilepsie temporale par analyse de l’onde P300

Introduction L’epilepsie temporale (ET) s’accompagne de troubles attentionnels qu’il est possible d’explorer en electrophysiologie par l’onde P300. La localisation des generateurs de la P300 reste mal connue. Objectifs Comparer les sources de la P300 entre patients ET et sujets sains et determiner s’il existe une relation entre la lateralisation du foyer epileptique et les generateurs de l’onde. Methodes 10 patients ET et 10 sujets sains beneficierent d’un enregistrement EEG haute resolution (128 voies). Les caracteristiques de la P300 (latence, amplitude) furent mesurees au cours d’un paradigme oddball auditif et visuel. Les generateurs furent localises sur des IRM individuelles par la methode LORETA. Resultats Nous avons retrouve une augmentation de la latence et une diminution d’amplitude de la P300 dans l’ET. Par rapport aux sujets sains, les sources temporo-mesiales etaient plus rares chez les patients ET, au profit des sources temporales externes. Cette reduction apparaissait plus nette du cote du foyer epileptique. Discussion La reduction des generateurs temporo-mesiaux dans l’ET pourrait refleter une dysfonction corticale locale, secondaire a l’epilepsie et une reorganisation fonctionnelle des structures impliquees dans l’attention comme cela a deja ete montre dans la memoire episodique. La lateralisation de ces modifications est en faveur d’une implication directe du foyer epileptique sur la reduction des sources et sur les troubles attentionnels. Conclusion Le dysfonctionnement temporo-mesial pourrait etre en partie responsable des troubles attentionnels dans l’epilepsie temporale, malgre une reorganisation des reseaux attentionnels chez ces patients.

H - 5 Mélanome malin leptomeningé

Introduction Les leptomeningites et pachymeningites peuvent etre secondaires a de nombreuses etiologies. Nous rapportons le cas rare d’un melanome malin leptomeninge. Observation Dossier n° 06-277 : Une femme de 24 ans consulta pour cephalees et deficits transitoires hemicorporels a bascule. L’IRM cerebrale identifia une leptomeningite diffuse, l’analyse du LCR etait normale. Six mois plus tard, le tableau s’enrichit d’un ralentissement psychomoteur, d’un syndrome cerebelleux, d’une hypertension intracrânienne avec œdeme papillaire au fond d’œil. Une seconde IRM objectiva une majoration de la leptomeningite, avec pachymeningite. L’examen du LCR retrouvait des lymphocytes sans cellule anormale, avec hyperproteinorrachie, hypoglycorachie, normochlorurorachie. L’EEG identifia des foyers epileptiques temporaux gauche et frontal droit, tres actifs, et un traitement par lamotrigine fut debute, ameliorant les episodes deficitaires a bascule. Le bilan etiologique de la leptomeningite fut negatif. Deux mois plus tard, l’apparition d’une lesion sous-corticale frontoparietale droite conduit a la realisation d’une biopsie meningee, identifiant des cellules melanomateuses malignes. Aucun melanome primitif cutaneo-muqueux n’etant retrouve, on conclut au diagnostic de melanome malin leptomeninge (MML). La patiente fut traitee par chimiotherapie (fotemustine), avec une reponse initiale favorable, suivie d’une rechute severe rapide avec coma. Discussion Les melanomes malins primitifs du systeme nerveux central (SNC) representent 1 p. 100 des melanomes. Ils peuvent se presenter sous deux formes : les MML diffus, de diagnostic souvent tardif, et les lesions nodulaires intraparenchymateuses, de meilleur pronostic. Le diagnostic de melanome malin primitif du SNC ne peut etre pose qu’en l’absence de toute lesion primitive extra-neurologique (cutanee ou muqueuse). Conclusion Devant une leptomeningite a bilan etiologique negatif, la realisation d’une biopsie meningee peut permettre de poser le diagnostic rare de MML.