References of "Luxen, André"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailRadiochemical synthesis and tissue distribution of p-[F-18]DMPPF, a new 5-HT1A ligand for PET, in rats
Defraiteur, Caroline; Lemaire, Christian ULg; Luxen, André ULg et al

in Nuclear Medicine & Biology (2006), 33(5), 667-675

Several studies have demonstrated the potential of p-[F-18]MPPF as a radiophanilaceutical to study the 5-HT1A receptor family in animals and humans. A structural modification leading to a higher ... [more ▼]

Several studies have demonstrated the potential of p-[F-18]MPPF as a radiophanilaceutical to study the 5-HT1A receptor family in animals and humans. A structural modification leading to a higher radioactive signal at an equipotent dose would greatly enhance this potential. With this goal, the desmethylated 4-(2'-methoxyphenyl)-1-[2'-[N-(2"-pyridinyl)-p-fluorobenzamidolethyl]-piperazine (p-MPPF), identified as p-DMPPF, was synthesized, labeled with fluorine-18 and evaluated through ex vivo tissue distribution in rats. The new compounds p-DMPPF, p-DMPPNO2, MEM-p-MPPF and MEM-p-MPPNO2 were isolated and fully identified (H-1 and C-13 NMR, LC-MS). The final compound, p-[F-18]DMPPF, was obtained ready for injection, with an overall radiochemical yield of 10% (EOB corrected) within 90 min and a specific activity of 62 GBq/mu mol. Tissue distributions showed that the carbon-fluorine bond was stable in vivo and that this compound could cross the blood-brain barrier. For kidney, lung, heart, spleen, bone, testicle, liver and muscle, the percentage of injected dose per gram of tissue obtained with p-[F-18]DMPPF was of the same order of magnitude as that of p-[F-18]MPPF. The amount of radioactivity reaching the brain was much higher (approximately fivefold at 60 min) for p-[F-18]DMPPF compared with p-[F-18]MPPF, which was taken as reference. The distribution and specificity were in total agreement with the known localization of 5-HT1A receptors in rats. The radioactivity increase was more important for specific tissues (hippocampus and frontal cortex) than for cerebellum or striatum, leading to better contrast (hippocampus/cerebellum=5.8 at 60 min). The levels of metabolites found in plasma showed that p-[F-18]DMPPF appears to be less metabolized than p-[F-18]MPPF. p-[F-18]DMPPF deserves further evaluation as a radiopharmaceutical candidate. (c) 2006 Elsevier Inc. All rights reserved. [less ▲]

Detailed reference viewed: 133 (6 ULg)
Full Text
Peer Reviewed
See detailImplicit oculomotor sequence learning in humans: Time course of offline processing
Albouy, Geneviève ULg; Ruby, P.; Phillips, Christophe ULg et al

in Brain Research (2006), 1090

Studies of manual and digital sequence learning indicate that motor memories continue to be processed after training has ended, following a succession of identifiable steps. However, it is not known ... [more ▼]

Studies of manual and digital sequence learning indicate that motor memories continue to be processed after training has ended, following a succession of identifiable steps. However, it is not known whether this offline memory processing constitutes a basic feature of motor learning and generalizes to the implicit learning of a sequence of eye movements. To assess this hypothesis, we have created the serial oculomotor reaction time task (SORT). Participants were trained to the SORT then tested after either 30 min, 5 h or 24 h. During training, ocular reaction times decreased monotonically over practice of a repeated sequence, then increased when a different sequence was displayed, demonstrating oculomotor learning of the trained sequence. When tested 30 min after training, a significant gain in oculomotor performance was observed irrespective of the sequence learning. This gain was no longer present after 5 h. Remarkably, a gain in performance specific to the learned sequence emerged only 24 h after training. After testing, a generation task confirmed that most subjects learned implicitly the regularities of the sequence. Our results show that, as for manual or digital sequences, oculomotor sequences can be implicitly learned. The offline processing of oculomotor memories follows distinct stages in a way similar to those observed after manual or digital sequence learning. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 29 (6 ULg)
See detailSynthesis of anhydro-muramic acid derivatives as substrates for MurNAc amidase
Mercier, Frédéric; Lemaire, Christian ULg; Plenevaux, Alain ULg et al

Poster (2006, May 17)

Detailed reference viewed: 9 (0 ULg)
Full Text
Peer Reviewed
See detailSleep after spatial learning promotes covert reorganization of brain activity
Orban, Pierre ULg; Rauchs, Géraldine; Balteau, Evelyne ULg et al

in Proceedings of the National Academy of Sciences of the United States of America (2006), 103(18), 7124-7129

Sleep promotes the integration of recently acquired spatial memories into cerebral networks for the long term. In this study, we examined how sleep deprivation hinders this consolidation process. Using ... [more ▼]

Sleep promotes the integration of recently acquired spatial memories into cerebral networks for the long term. In this study, we examined how sleep deprivation hinders this consolidation process. Using functional MRI, we mapped regional cerebral activity during place-finding navigation in a virtual town, immediately after learning and 3 days later, in subjects either allowed regular sleep (RS) or totally sleep-deprived (TSD) on the first posttraining night. At immediate and delayed retrieval, place-finding navigation elicited increased brain activity in an extended hippocamponeocortical network in both RS and TSD subjects. Behavioral performance was equivalent between groups. However, striatal navigation-related activity increased more at delayed retrieval in RS than in TSD subjects. Furthermore, correlations between striatal response and behavioral performance, as well as functional connectivity between the striatum and the hippocampus, were modulated by posttraining sleep. These data suggest that brain activity is restructured during sleep in such a way that navigation in the virtual environment, initially related to a hippocampus-dependent spatial strategy, becomes progressively contingent in part on a response-based strategy mediated by the striatum. Both neural strategies eventually relate to equivalent performance levels, indicating that covert reorganization of brain patterns underlying navigation after sleep is not necessarily accompanied by overt changes in behavior. [less ▲]

Detailed reference viewed: 21 (1 ULg)
Full Text
Peer Reviewed
See detailDecomposition of metabolic brain clusters in the frontal variant of frontotemporal dementia
Salmon, Eric ULg; Kerrouche, Nacer; Herholz, Karl et al

in NeuroImage (2006), 30(3), 871-878

Previous studies that measured brain activity in frontotemporal dementia (FTD) used univariate analyses, examining each region of interest separately. We explored in a multicenter European research ... [more ▼]

Previous studies that measured brain activity in frontotemporal dementia (FTD) used univariate analyses, examining each region of interest separately. We explored in a multicenter European research program the principal brain clusters characterized by a common variability in cerebral metabolism in FTD. Seventy patients with frontal variant (fv) FTD were selected according to international clinical recommendations; principal component analysis (PCA) was performed on FDG-PET metabolic images, looking for covariance clusters in this large population. A first metabolic cluster included most of the lateral and medial prefrontal cortex, bilaterally; PC1 scores correlated with performances on memory and executive neuropsychological tasks. Moreover, FDG-PET images in fv-FTD were further characterized by a metabolic covariance in two clusters comprising the subcallosal medial frontal region, the temporal pole, medial temporal structures and the striatum, separately in the left and in the right hemisphere. The study provides original data-driven arguments for metabolic involvement of separate brain clusters in the rostral limbic system, corresponding to pathological poles differentially affected in each FTD patient. [less ▲]

Detailed reference viewed: 28 (0 ULg)
Full Text
Peer Reviewed
See detailOffline persistence of memory-related cerebral activity during active wakefulness
Peigneux, Philippe ULg; Orban, Pierre ULg; Balteau, Evelyne ULg et al

in PLoS Biology (2006), 4(4), 100

Much remains to be discovered about the fate of recent memories in the human brain. Several studies have reported the reactivation of learning-related cerebral activity during post-training sleep ... [more ▼]

Much remains to be discovered about the fate of recent memories in the human brain. Several studies have reported the reactivation of learning-related cerebral activity during post-training sleep, suggesting that sleep plays a role in the offline processing and consolidation of memory. However, little is known about how new information is maintained and processed during post-training wakefulness before sleep, while the brain is actively engaged in other cognitive activities. We show, using functional magnetic resonance imaging, that brain activity elicited during a new learning episode modulates brain responses to an unrelated cognitive task, during the waking period following the end of training. This post-training activity evolves in learning-related cerebral structures, in which functional connections with other brain regions are gradually established or reinforced. It also correlates with behavioral performance. These processes follow a different time course for hippocampus-dependent and hippocampus-independent memories. Our experimental approach allowed the characterization of the offline evolution of the cerebral correlates of recent memories, without the confounding effect of concurrent practice of the learned material. Results indicate that the human brain has already extensively processed recent memories during the first hours of post-training wakefulness, even when simultaneously coping with unrelated cognitive demands. [less ▲]

Detailed reference viewed: 78 (10 ULg)
Full Text
Peer Reviewed
See detailDEVELOPPEMENT D'INHIBITEURS SELECTIFS DE LA TRYPTOPHANE HYDROXYLASE
Giacomelli, Fabrice ULg; Luxen, André ULg; Lemaire, Christian ULg et al

Conference (2006, February 03)

Comprendre la façon dont le cerveau travaille et en particulier le mode de communication de ses cellules est un rêve que beaucoup de chercheurs caressent. A l’heure actuelle, une des rares certitudes à ... [more ▼]

Comprendre la façon dont le cerveau travaille et en particulier le mode de communication de ses cellules est un rêve que beaucoup de chercheurs caressent. A l’heure actuelle, une des rares certitudes à son sujet est qu’un de ses modes de transmission d’informations utilise des « messagers » chimiques appelés neurotransmetteurs. Parmi ceux-ci, la sérotonine (5-HT) revêt une importance particulière. En effet, la 5-HT est impliquée dans de nombreuses fonctions (apprentissage, locomotion, sommeil,…) et pathologies (dépressions, démences, schizophrénies,…). Dès lors, l'étude in vivo chez l'homme des neurones sérotoninergiques ainsi que la quantification de la vitesse de biosynthèse de la 5-HT sont des domaines d'études fondamentaux pour lesquels la tomographie à émission de positons (TEP) constitue un outil de choix. Pour mener à bien ces différentes expérimentations, deux stratégies sont envisageables : - L’emploi d'un traceur capable de suivre la chaîne métabolique du tryptophane conduisant à la 5-HT tout en évitant les autres voies métaboliques. - L’utilisation d'un inhibiteur de la TrpOH (enzyme limitant du processus). Dans le cadre de cette présentation, nous nous intéresserons plus particulièrement à la deuxième stratégie. [less ▲]

Detailed reference viewed: 34 (3 ULg)
See detailThe role of sleep in the consolidation of emotional memories W
Sterpenich, V.; Albouy, G.; Boly, M. et al

Poster (2006)

Detailed reference viewed: 7 (1 ULg)
Full Text
Peer Reviewed
See detailL-amino acid load to enhance PET differentiation between tumor and inflammation: an in vitro study on (18)F-FET uptake.
Laique, S.; Egrise, D.; Monclus, M. et al

in Contrast Media & Molecular Imaging (2006), 1(5), 212-20

Labeled amino acids (AA) are tumor tracers for use in nuclear medecine. O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET) is transported by the L-system, known to function as an exchanger. In vitro utilization of ... [more ▼]

Labeled amino acids (AA) are tumor tracers for use in nuclear medecine. O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET) is transported by the L-system, known to function as an exchanger. In vitro utilization of FET, after a preload or prior to an afterload of non radioactive L-amino acids, was evaluated in order to measure the potential effects of AA content on the distinction between tumor and inflammatory lesions. Cellular uptake of FET was studied on rat osteosarcoma cells (ROS 17/2.8) and human leukocytes, initially loaded with nonradioactive L-tyrosine or L-methionine. FET efflux was evaluated from cells loaded with nonradioactive L-phenylalanine after tracer uptake. ROS 17/2.8 showed a higher sensitivity to preload and afterload effects on cellular FET content as compared with the leukocytes. We conclude that preload with L-tyrosine, prior to the administration of FET, may be a potential procedure to improve PET differentiation between tumor and inflammatory lesions. [less ▲]

Detailed reference viewed: 26 (0 ULg)
Full Text
Peer Reviewed
See detailImproved PRESS sequence for lactate detection in the human vitreous body
Balteau, Evelyne ULg; COLLIGNON, Nathalie ULg; Robe, Pierre ULg et al

in Proceedings of the International Society for Magnetic Resonance in Medicine (2006), 14

Detailed reference viewed: 57 (8 ULg)
Full Text
Peer Reviewed
See detailHippocampal response at training promotes insight after sleep
Darsaud, Annabelle; Balteau, Evelyne ULg; Desseilles, Martin ULg et al

in NeuroImage (2006), 31(Suppl. 1),

Detailed reference viewed: 11 (1 ULg)
Peer Reviewed
See detailThe role of sleep in the consolidation of emotional memories in humans : a fMRI study
Sterpenich, Virginie; Albouy, Geneviève ULg; Boly, Mélanie ULg et al

Poster (2006)

Detailed reference viewed: 17 (5 ULg)
Full Text
Peer Reviewed
See detailDaytime light exposure dynamically enhances brain responses.
Vandewalle, Gilles ULg; Balteau, Evelyne ULg; Phillips, Christophe ULg et al

in Current Biology (2006), 16(16), 1616-21

In humans, light enhances both alertness and performance during nighttime and daytime [1-4] and influences regional brain function [5]. These effects do not correspond to classical visual responses but ... [more ▼]

In humans, light enhances both alertness and performance during nighttime and daytime [1-4] and influences regional brain function [5]. These effects do not correspond to classical visual responses but involve a non-image forming (NIF) system, which elicits greater endocrine, physiological, neurophysiological, and behavioral responses to shorter light wavelengths than to wavelengths geared toward the visual system [6-11]. During daytime, the neural changes induced by light exposure, and their time courses, are largely unknown. With functional magnetic resonance imaging (fMRI), we characterized the neural correlates of the alerting effect of daytime light by assessing the responses to an auditory oddball task [12-15], before and after a short exposure to a bright white light. Light-induced improvement in subjective alertness was linearly related to responses in the posterior thalamus. In addition, light enhanced responses in a set of cortical areas supporting attentional oddball effects, and it prevented decreases of activity otherwise observed during continuous darkness. Responses to light were remarkably dynamic. They declined within minutes after the end of the light stimulus, following various region-specific time courses. These findings suggest that light can modulate activity of subcortical structures involved in alertness, thereby dynamically promoting cortical activity in networks involved in ongoing nonvisual cognitive processes. [less ▲]

Detailed reference viewed: 47 (4 ULg)
Full Text
Peer Reviewed
See detailBrain response to one's own name in vegetative state, minimally conscious state and locked-in syndrome
Perrin, F.; Schnakers, Caroline ULg; Schabus, M. et al

in Archives of Neurology (2006), 63

Detailed reference viewed: 35 (7 ULg)
Peer Reviewed
See detailSynthesis of protected meso-diaminopimelic acid.
Teller, N.; Lemaire, Christian ULg; Plenevaux, Alain ULg et al

Poster (2005, October 10)

Detailed reference viewed: 13 (2 ULg)
Peer Reviewed
See detailSynthesis of anhydro-muranic acid derivatives as substrates for MurNAc amidase.
Mercier, F.; Lemaire, Christian ULg; Plenevaux, Alain ULg et al

Poster (2005, October 10)

Detailed reference viewed: 24 (7 ULg)
Full Text
Peer Reviewed
See detailExploring the unity and diversity of the neural substrates of executive functioning
Collette, Fabienne ULg; Van der Linden, Martial ULg; Laureys, Steven ULg et al

in Human Brain Mapping (2005), 25(4), 409-423

Previous studies exploring the neural substrates of executive functioning used task-specific analyses, which might not be the most appropriate approach due to the difficulty of precisely isolating ... [more ▼]

Previous studies exploring the neural substrates of executive functioning used task-specific analyses, which might not be the most appropriate approach due to the difficulty of precisely isolating executive functions. Consequently, the aim of this study was to use positron emission tomography (PET) to reexamine by conjunction and interaction paradigms the cerebral areas associated with three executive processes (updating, shifting, and inhibition). Three conjunction analyses allowed us to isolate the cerebral areas common to tasks selected to tap into the same executive process. A global conjunction analysis demonstrated that foci of activation common to all tasks were observed in the right intraparietal sulcus, the left superior parietal gyrus, and at a lower statistical threshold, the left lateral prefrontal cortex. These regions thus seem to play a general role in executive functioning. The right intraparietal sulcus seems to play a role in selective attention to relevant stimuli and in suppression of irrelevant information. The left superior parietal region is involved in amodal switching/integration processes. One hypothesis regarding the functional role of the lateral prefrontal cortex is that monitoring and temporal organization of cognitive processes are necessary to carry out ongoing tasks. Finally, interaction analyses showed that specific prefrontal cerebral areas were associated with each executive process. The results of this neuro-imaging study are in agreement with cognitive studies demonstrating that executive functioning is characterized by both unity and diversity of processes. [less ▲]

Detailed reference viewed: 87 (4 ULg)
Full Text
Peer Reviewed
See detailInvolvement of both prefrontal and inferior parietal cortex in dual-task performance
Collette, Fabienne ULg; Olivier, L.; Van der Linden, Martial ULg et al

in Cognitive Brain Research (2005), 24(2), 237-251

This PET study explored the neural substrate of both dual-task management and integration task using single tasks that are known not to evoke any prefrontal activation. The paradigm included two simple ... [more ▼]

This PET study explored the neural substrate of both dual-task management and integration task using single tasks that are known not to evoke any prefrontal activation. The paradigm included two simple (visual and auditory) discrimination tasks, a dual task and an integration task (requiring simultaneous visual and auditory discrimination), and baseline tasks (passive viewing and hearing). Data were analyzed using SPM99. As predicted, the comparison of each single task to the baseline task showed no activity in prefrontal areas. The comparison of the dual task to the single tasks demonstrated left-sided foci of activity in the frontal gyrus (BA 9/46, BA 10/47 and BA 6), inferior parietal gyrus (BA 40), and cerebellum. By reference to previous neuroimaging studies, BA 9/46 was associated with the coordinated manipulation of simultaneously presented information, BA 10/47 with selection processes, BA 6 with articulatory rehearsal, and BA 40 with attentional shifting. Globally similar regions were found for the integration task, except that the inferior parietal gyrus was not recruited. These results confirm the hypothesis that the left prefrontal cortex is implicated in dual-task performance. Moreover, the involvement of a parietal area in the dual task is in keeping with the hypothesis that a parieto-frontal network sustains executive functioning. [less ▲]

Detailed reference viewed: 67 (0 ULg)