References of "Luxen, André"
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See detailAre spatial memories strengthened in the human hippocampus during slow wave sleep?
Peigneux, Philippe ULg; Laureys, Steven ULg; Fuchs, Sonia et al

in Neuron (2004), 44(3), 535-545

In rats, the firing sequences observed in hippocampal ensembles during spatial learning are replayed during subsequent sleep, suggesting a role for posttraining sleep periods in the offline processing of ... [more ▼]

In rats, the firing sequences observed in hippocampal ensembles during spatial learning are replayed during subsequent sleep, suggesting a role for posttraining sleep periods in the offline processing of spatial memories. Here, using regional cerebral blood flow measurements, we show that, in humans, hippocampal areas that are activated during route learning in a virtual town are likewise activated during subsequent slow wave sleep. Most importantly, we found that the amount of hippocampal activity expressed during slow wave sleep positively correlates with the improvement of performance in route retrieval on the next day. These findings suggest that learning-dependent modulation in hippocampal activity during human sleep reflects the offline processing of recent episodic and spatial memory traces, which eventually leads to the plastic changes underlying the subsequent improvement in performance. [less ▲]

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See detailFluorinated tracers for imaging cancer with positron emission tomography
Couturier, Olivier; Luxen, André ULg; Chatal, Jean-François et al

in European Journal of Nuclear Medicine and Molecular Imaging (2004), 31(8), 1182-1206

2-[F-18]fluoro-2-deoxy-D-glucose (FDG) is currently the only fluorinated tracer used in routine clinical positron emission tomography (PET). Fluorine-18 is considered the ideal radioisotope for PET ... [more ▼]

2-[F-18]fluoro-2-deoxy-D-glucose (FDG) is currently the only fluorinated tracer used in routine clinical positron emission tomography (PET). Fluorine-18 is considered the ideal radioisotope for PET imaging owing to the low positron energy (0.64 MeV), which not only limits the dose rate to the patient but also results in a relatively short range of emission in tissue, thereby providing high-resolution images. Further, the 110-min physical half-life allows for high-yield radiosynthesis, transport from the production site to the imaging site and imaging protocols that may span hours, which permits dynamic studies and assessment of potentially fairly slow metabolic processes. The synthesis of fluorinated tracers as an alternative to FDG was initially tested using nucleophilic fluorination of the molecule, as performed when radiolabelling with iodine-124 or bromide-76. However, in addition to being long, with multiple steps, this procedure is not recommended for bioactive molecules containing reactive groups such as amine or thiol groups. Radiochemical yields are also often low. More recently, radiosynthesis from prosthetic group precursors, which allows easier radiolabelling of biomolecules, has led to the development of numerous fluorinated tracers. Given the wide availability of 18F, such tracers may well develop into important routine tracers. This article is a review of the literature concerning fluorinated radiotracers recently developed and under investigation for possible PET imaging in cancer patients. Two groups can be distinguished. The first includes "generalist" tracers, i.e. tracers amenable to use in a wide variety of tumours and indications, very similar in this respect to FDG. These are tracers for non-specific cell metabolism, such as protein synthesis, amino acid transport, nucleic acid synthesis or membrane component synthesis. The second group consists of "specific" tracers for receptor expression (i.e. oestrogens or somatostatin), cell hypoxia or bone metabolism. [less ▲]

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See detailHighly enantioselective synthesis of no-carrier-added 6-[18F]Fluoro-L-dopa by chiral phase-transfer alkylation
Lemaire, Christian ULg; Gillet, Steve; Guillouet, Stéphane et al

in European Journal of Organic Chemistry (2004), (13), 2899-2904

[F-18]Fluoro-L-dopa, an important radiopharmaceutical for positron emission tomography (PET), has been synthesized using a phase-transfer alkylation reaction. A chiral quaternary ammonium salt derived ... [more ▼]

[F-18]Fluoro-L-dopa, an important radiopharmaceutical for positron emission tomography (PET), has been synthesized using a phase-transfer alkylation reaction. A chiral quaternary ammonium salt derived from a Cinchona alkaloid served as phase-transfer catalyst for the enantioselective alkylation of a glycine derivative. The active methylene group of this Schiff-base substrate was deprotonated with cesium hydroxide and rapidly alkylated by the 2-[F-18]fluoro-4,5-dimethoxybenzyl halide (X = Br, I). The reaction proceeded with high yield (> 90%) at 0 degreesC or room temperature in various solvents such as toluene or dichloromethane. Preparation of the [F-18]alkylating agent on a solid support was developed. After labelling, the labeled [F-18]fluoroveratraldehyde was trapped on a (t)C18 cartridge and then converted on the cartridge into the corresponding benzyl halide derivatives by addition of aqueous sodium borohydride and gaseous hydrobromic or -iodic acid. Hydrolysis and purification by preparative HPLC made 6-[F-18]fluoro-L-dopa ready for human injection in a 25-30% decay-corrected radiochemical yield in a synthesis time of 100 min. The product was found to be chemically, radiochemically and enantiomerically pure (ee > 95%). (C) Wiley-VCH Verlag GmbH [less ▲]

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See detailImaging a cognitive model of apraxia: The neural substrate of gesture-specific cognitive processes
Peigneux, Philippe ULg; Van der Linden, Martial ULg; Garraux, Gaëtan ULg et al

in Human Brain Mapping (2004), 21(3), 119-142

The present study aimed to ascertain the neuroanatomical basis of an influential neuropsychological model for upper limb apraxia [Rothi LJ, et al. The Neuropsychology of Action. 1997. Hove, UK: Psychology ... [more ▼]

The present study aimed to ascertain the neuroanatomical basis of an influential neuropsychological model for upper limb apraxia [Rothi LJ, et al. The Neuropsychology of Action. 1997. Hove, UK: Psychology Press]. Regional cerebral blood flow was measured in healthy volunteers using (H2O)-O-15 PET during performance of four tasks commonly used for testing upper limb apraxia, i.e., pantomime of familiar gestures on verbal command, imitation of familiar gestures, imitation of novel gestures, and an action-semantic task that consisted in matching objects for functional use. We also re-analysed data from a previous PET study in which we investigated the neural basis. of the visual analysis of gestures. First; we found that two sets of discrete brain areas are predominantly engaged in the imitation of familiar and novel gestures, respectively. Segregated brain activation for novel gesture mutation concur with neuropsychological reports to support the hypothesis that knowledge about the organization of the human body mediates the transition from visual perception to motor execution when imitating novel gestures [Goldenberg Neuropsychologia 1995;35.63-72]. Second, conjunction analyses revealed distinctive neural bases for most of the gesture-specific cognitive processes proposed in this cognitive model of upper limb apraxia. However, a functional analysis of brain imaging data suggested that one single memory store may be used for "to be-perceived" and "to-be-produced" gestural representations, departing from Rothi et al.'s proposal. Based on the above considerations, we suggest and discuss a revised model for upper limb apraxia that might best account for both brain imaging findings and neuropsychological dissociations reported in the apraxia literature. (C) 2004 Wiley-Liss, Inc. [less ▲]

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See detailAuditory processing in severely brain injured patients: differences between the minimally conscious state and the persistent vegetative state.
Boly, Mélanie ULg; FAYMONVILLE, Marie-Elisabeth ULg; Peigneux, Philippe ULg et al

in Archives of Neurology (2004), 61(2), 233-8

BACKGROUND: The minimally conscious state (MCS) is a recently defined clinical condition; it differs from the persistent vegetative state (PVS) by the presence of inconsistent, but clearly discernible ... [more ▼]

BACKGROUND: The minimally conscious state (MCS) is a recently defined clinical condition; it differs from the persistent vegetative state (PVS) by the presence of inconsistent, but clearly discernible, behavioral evidence of consciousness. OBJECTIVE: To study auditory processing among patients who are in an MCS, patients who are in a PVS, and healthy control subjects. METHODS: By means of (15)O-radiolabeled water-positron emission tomography, we measured changes in regional cerebral blood flow induced by auditory click stimuli in 5 patients in an MCS, 15 patients in a PVS, and 18 healthy controls. RESULTS: In both patients in an MCS and the healthy controls, auditory stimulation activated bilateral superior temporal gyri (Brodmann areas 41, 42, and 22). In patients in a PVS, the activation was restricted to Brodmann areas 41 and 42 bilaterally. We also showed that, compared with patients in a PVS, patients in an MCS demonstrated a stronger functional connectivity between the secondary auditory cortex and temporal and prefrontal association cortices. CONCLUSIONS: Although assumptions about the level of consciousness in severely brain injured patients are difficult to make, our findings suggest that the cerebral activity observed in patients in an MCS is more likely to lead to higher-order integrative processes, thought to be necessary for the gain of conscious auditory perception. [less ▲]

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See detailResidual cerebral functioning in the vegetative state
Laureys, Steven ULg; Faymonville, Marie-Elisabeth ULg; De Tiège, X. et al

in Arco di Giano (2004)

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See detailTissue distribution and metabolism of D-p-[18F]MPPF in rats.
Defraiteur, C.; Muroni, S.; Lemaire, Christian ULg et al

in Journal of Nuclear Medicine : Official Publication, Society of Nuclear Medicine (2004), 45(S2), 444

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See detailNonvisual responses to light exposure in the human brain during the circadian night
Perrin, Fabien; Peigneux, Philippe ULg; Fuchs, Sonia ULg et al

in Current Biology (2004), 14(20), 1842-6

The brain processes light information to visually represent the environment but also to detect changes in ambient light level. The latter information induces non-image-forming responses and exerts ... [more ▼]

The brain processes light information to visually represent the environment but also to detect changes in ambient light level. The latter information induces non-image-forming responses and exerts powerful effects on physiology such as synchronization of the circadian clock and suppression of melatonin. In rodents, irradiance information is transduced from a discrete subset of photosensitive retinal ganglion cells via the retinohypothalamic tract to various hypothalamic and brainstem regulatory structures including the hypothalamic suprachiasmatic nuclei, the master circadian pacemaker. In humans, light also acutely modulates alertness, but the cerebral correlates of this effect are unknown. We assessed regional cerebral blood flow in 13 subjects attending to auditory and visual stimuli in near darkness following light exposures (>8000 lux) of different durations (0.5, 17, 16.5, and 0 min) during the biological night. The bright broadband polychromatic light suppressed melatonin and enhanced alertness. Functional imaging revealed that a large-scale occipito-parietal attention network, including the right intraparietal sulcus, was more active in proportion to the duration of light exposures preceding the scans. Activity in the hypothalamus decreased in proportion to previous illumination. These findings have important implications for understanding the effects of light on human behavior. [less ▲]

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See detailLearned material content and acquisition level modulate cerebral reactivation during posttraining rapid-eye-movements sleep
Peigneux, Philippe ULg; Laureys, Steven ULg; Fuchs, Sonia et al

in NeuroImage (2003), 20(1), 125-134

We have previously shown that several brain areas are activated both during sequence learning at wake and during subsequent rapid-eye-movements (REM) sleep (Nat. Neurosci. 3 (2000) 831-836), suggesting ... [more ▼]

We have previously shown that several brain areas are activated both during sequence learning at wake and during subsequent rapid-eye-movements (REM) sleep (Nat. Neurosci. 3 (2000) 831-836), suggesting that REM sleep participates in the reprocessing of recent memory traces in humans. However, the nature of the reprocessed information remains open. Here, we show that regional cerebral reactivation during posttraining REM sleep is not merely related to the acquisition of basic visuomotor skills during prior practice of the serial reaction time task, but rather to the implicit acquisition of the probabilistic rules that defined stimulus sequences. Moreover, functional connections between the reactivated cuneus and the striatum-the latter being critical for implicit sequence learning-are reinforced during REM sleep after practice on a probabilistic rather than on a random sequence of stimuli. Our results therefore support the hypothesis that REM sleep is deeply involved in the reprocessing and optimization of the high-order information contained in the material to be learned. In addition, we show that the level of acquisition of probabilistic rules attained prior to sleep is correlated to the increase in regional cerebral blood flow during subsequent REM sleep. This suggests that posttraining cerebral reactivation is modulated by the strength of the memory traces developed during the learning episode. Our data provide the first experimental evidence for a link between behavioral performance and cerebral reactivation during REM sleep. (C) 2003 Elsevier Inc. All rights reserved. [less ▲]

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See detailRadiochemical Synthesis of p-[18F]Desmethyl-MPPF (p-[18F]D-MPPF) for the Study of 5-HT1A Receptors
Defraiteur, Caroline; Plenevaux, Alain ULg; Lemaire, Christian ULg et al

in Journal of Labelled Compounds & Radiopharmaceuticals (2003, August), 46(S1), 157

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See detailPhonological short-term memory networks following recovery from Landau and Kleffner syndrome
Majerus, Steve ULg; Laureys, Steven ULg; Collette, Fabienne ULg et al

in Human Brain Mapping (2003), 19(3), 133-144

Landau-Kleffner syndrome (LKS) is a rare acquired aphasia occurring in otherwise healthy children, together with spike-wave discharges predominating over superior temporal regions and activated by sleep ... [more ▼]

Landau-Kleffner syndrome (LKS) is a rare acquired aphasia occurring in otherwise healthy children, together with spike-wave discharges predominating over superior temporal regions and activated by sleep. Although the outcome of language abilities is variable, a residual impairment in verbal short-term memory (STM) is frequent. This STM deficit might be related to the persistent dysfunction of those temporal lobe regions where epileptic discharges were observed during the active phase of the disorder. We tested this hypothesis by measuring brain activation during immediate serial recall of lists of 4 words, compared to single word repetition, using H(2) (15)O positron emission tomography (PET), in 3 LKS patients after recovery and in 14 healthy controls. The patients (TG, JPH, and DC) had shown abnormally increased or decreased glucose metabolism in left or right superior temporal gyrus (STG) at different stages during the active phase of their disease. At the time of this study, the patients were 6-10 years from the active phase of LKS. Results showed that Patients JPH and DC had impaired performance in the STM condition, whereas TG showed near normal performance. PET data showed that JPH and DC activated significantly less than controls left and right posterior STG. TG, having near normal STM performance, showed increased activity in the posterior part of the right STG. These data suggest that impaired verbal STM at late outcome of LKS might indeed be related to a persistent decrease of activity in those posterior superior temporal gyri that were involved in the epileptic focus during the active phase. [less ▲]

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See detailIncreased cerebral functional connectivity underlying the antinociceptive effects of hypnosis
Faymonville, Marie-Elisabeth ULg; Roediger, Laurence ULg; Del Fiore, Guy et al

in Cognitive Brain Research (2003), 17(2), 255-262

The neural mechanisms underlying the antinociceptive effects of hypnosis are not well understood. Using positron emission tomography (PET), we recently showed that the activity in the anterior cingulate ... [more ▼]

The neural mechanisms underlying the antinociceptive effects of hypnosis are not well understood. Using positron emission tomography (PET), we recently showed that the activity in the anterior cingulate cortex (midcingulate area 24a') covaries with the hypnosis-induced reduction of affective and sensory responses to noxious thermal stimulation [Faymonville et al., Anesthesiology 92 (2000) 1257-1267]. In the present study, we assessed changes in cerebral functional connectivity related to the hypnotic state, compared to simple distraction and the resting state. Nineteen highly hypnotizable right-handed volunteers were studied using (H2O)-O-15-PET. The experimental conditions were hot noxious or warm non-noxious stimulation of the right hand during resting state, mental imagery and hypnotic state. Using a psychophysiological interaction analysis, we identified brain areas that would respond to noxious stimulations under the modulatory action of the midcingulate cortex in, and only in, the hypnotic state. Hypnosis, compared to the resting state, reduced pain perception by 50%. Pain perception during rest and mental imagery was not significantly different. Analysis of PET data showed that the hypnotic state, compared to normal alertness (i.e., rest and mental imagery), significantly enhanced the functional modulation between midcingulate cortex and a large neural network encompassing bilateral insula, pregenual anterior cingulate cortex, pre-supplementary motor area, right prefrontal cortex and striatum, thalamus and brainstem. These findings point to a critical role for the midcingulate cortex in the modulation of a large cortical and subcortical network underlying its influence on sensory, affective, Cognitive and behavioral aspects of nociception, in the specific context of hypnosis. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

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See detailRadiosynthèses d'antagonistes des récepteurs 5-HT1A.
Defraiteur, C.; Plenevaux, Alain ULg; Lemaire, Christian ULg et al

Poster (2003, June 13)

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See detailMise au point de sondes pour l'étude du système sérotoninergique par tomographie à émission de positons (TEP)
Giacomelli, Fabrice ULg; Lemaire, Christian ULg; Plenevaux, Alain ULg et al

Poster (2003, June 13)

La quantification de la vitesse de biosynthèse de la sérotonine ainsi que l'étude in vivo chez l'homme sont, du fait de l'implication cruciale des neurones sérotoninergiques dans de nombreuses fonctions ... [more ▼]

La quantification de la vitesse de biosynthèse de la sérotonine ainsi que l'étude in vivo chez l'homme sont, du fait de l'implication cruciale des neurones sérotoninergiques dans de nombreuses fonctions et pathologies cérébrales, des domaines d'études fondamentaux pour lesquels la TEP constitue un outil de choix. Ces différentes expérimentations peuvent être conduites suivant deux optiques: (i) emploi d'un traceur capable de suivre la chaîne métabolique du tryptophane conduisant à la sérotonine tout en évitant les autres voies métaboliques. (ii) utilisation d'un inhibiteur de la tryptophane hydroxylase (TPOH), enzyme limitante du processus. [less ▲]

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See detailRadiosynthèse de dérivés du 7-[18F]fluoroindole
Otabashi, Muhammad ULg; Giacomelli, Fabrice ULg; Lemaire, Christian ULg et al

Poster (2003, June 13)

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See detailWhole-body tumor imaging using PET and 2-18F-fluoro-l-tyrosine: Preliminary evaluation and comparison with 18F-FDG
Hustinx, Roland ULg; Lemaire, Christian ULg; Jerusalem, Guy ULg et al

in Journal of Nuclear Medicine : Official Publication, Society of Nuclear Medicine (2003), 44(4), 533-539

18F-FDG PET imaging is now established as a valuable tool for evaluating cancer patients. However, a limitation of 18F-FDG is its absence of specificity for tumor. Both protein synthesis and amino acid ... [more ▼]

18F-FDG PET imaging is now established as a valuable tool for evaluating cancer patients. However, a limitation of 18F-FDG is its absence of specificity for tumor. Both protein synthesis and amino acid transport are enhanced in most tumor cells, but their metabolism is less affected in inflammation. We therefore decided to evaluate the ability of PET with 2-18F-fluoro-L-tyrosine (18F-TYR) to visualize cancer lesions in patients compared with 18F-FDG PET. Methods: 18F-FDG PET and 18F-TYR PET were performed on 23 patients with histologically proven malignancies (11 non-small cell lung cancers (NSCLCs), 10 lymphomas, and 2 head and neck carcinomas). Fully corrected, whole-body PET studies were obtained on separate days. 18F-FDG studies were performed after routine clinical fashion. 18F-TYR studies were started 36 ± 6 min after tracer injection and a second scan centered over a reference lesion was acquired after completion of the whole-body survey-on average, 87 min after injection. Standardized uptake values (SUVs) were calculated for all abnormal foci and for various normal structures. Results were compared with pathologic or correlative studies. Results: 18F-FDG PET correctly identified 54 malignant lesions, among which 36 were also visualized with 18F-TYR (67%). 18F-TYR did not detect any additional lesion. Tumor SUVs (SUVbw, 5.2 vs. 2.5), tumor-to-muscle (7.4 vs. 2.7), and tumor-to-mediastinum activity ratios (3 vs. 1.4) were higher with 18F-FDG than with 18F-TYR. Two of 11 NSCLCs and 4 of 10 lymphomas were understaged with 18F-TYR compared with 18F-FDG. Although the NSCLC lesions missed by 18F-TYR PET were small, several large lymphoma lesions did not accumulate the tracer. In 4 patients, 18F-TYR-positive lesions coexisted with 18F-TYR-negative lesions. There was a high physiologic 18F-TYR uptake by the pancreas (average SUVbw, 10.3) and the liver (average SUVbw, 6.3). Muscle and bone marrow uptakes were also higher with 18F-TYR than with 18F-FDG: average SUVbw, 1 versus 0.7 and 2.6 versus 1.8, respectively. There was no change over time in the 18F-TYR uptake by the tumors or the normal structures. Conclusion: 18F-TYR PET is not superior to 18F-FDG PET for staging patients with NSCLC and lymphomas. [less ▲]

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See detailNeural correlates of "hot" and "cold" emotional processing : a multilevel approach to the functional anatomy of emotion
Schaefer, Alexandre; Collette, Fabienne ULg; Philippot, Pierre et al

in Neuroimage (2003), 18(4), 938-949

The neural correlates of two hypothesized emotional processing modes, i.e., schematic and propositional modes, were investigated with positron emission tomography. Nineteen subjects performed an emotional ... [more ▼]

The neural correlates of two hypothesized emotional processing modes, i.e., schematic and propositional modes, were investigated with positron emission tomography. Nineteen subjects performed an emotional mental imagery task while mentally repeating sentences linked to the meaning of the imagery script. In the schematic conditions, participants repeated metaphoric sentences, whereas in the propositional conditions, the sentences were explicit questions about specific emotional appraisals of the imagery scenario. Five types of emotional scripts were proposed to the subjects (happiness, anger, affection, sadness, and a neutral scenario). The results supported the hypothesized distinction between schematic and propositional emotional processing modes. Specifically, schematic mode was associated with increased activity in the ventromedial prefrontal cortex whereas propositional mode was associated with activation of the anterolateral prefrontal cortex. In addition, interaction analyses showed that schematic versus propositional processing of happiness (compared with the neutral scenario) was associated with increased activity in the ventral striatum whereas "schematic anger" was tentatively associated with activation of the ventral pallidum. (C) 2003 Elsevier Science (USA). All rights reserved. [less ▲]

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