References of "Degueldre, Christian"
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See detailMemory Reactivation During Rapid Eye Movement (REM) Sleep Promotes Its Generalization and Integration in Cortical Stores
Sterpenich, Virginie; Schmidt, Christina ULg; Albouy, Genevièvre et al

in Sleep (2014), 37(6), 1061-1075

Memory reactivation appears to be a fundamental process in memory consolidation. Here, we tested the influence of memory reactivation during REM sleep on memory performance and brain responses at ... [more ▼]

Memory reactivation appears to be a fundamental process in memory consolidation. Here, we tested the influence of memory reactivation during REM sleep on memory performance and brain responses at retrieval in healthy human participants. Auditory cues were associated with pictures of faces during their encoding. These memory cues delivered during REM sleep enhanced subsequent accurate recollections but also false recognitions. These results suggest that reactivated memories interacted with semantically-related representations, and induced new creative associations, which subsequently reduced the distinction between new and previously encoded exemplars. Cues had no effect if presented during stage 2 sleep, or if they were not associated with faces during encoding. Functional MRI revealed that following exposure to conditioned cues during REM sleep, responses to faces during retrieval were enhanced both in a visual area and in a cortical region of multisensory (auditory-visual) convergence. These results show that reactivating memories during REM sleep enhances cortical responses during retrieval, suggesting the integration of recent memories within cortical circuits, favoring the generalization and schematization of the information. [less ▲]

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See detailPhotic memory for executive brain responses
Chellappa*, Sarah Laxhmi ULg; Ly*, Julien ULg; Meyer, Christelle ULg et al

in Proceedings of the National Academy of Sciences of the United States of America (2014), Epub ahead of print

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See detailMulticlass classification of FDG PET scans for the distinction between Parkinson's disease and atypical parkinsonian syndromes
Garraux, Gaëtan ULg; Phillips, Christophe ULg; Schrouff, Jessica ULg et al

in NeuroImage: Clinical (2013), 2

Most available pattern recognition methods in neuroimaging address binary classification problems. Here, we used relevance vector machine (RVM) in combination with booststrap resampling (‘bagging’) for ... [more ▼]

Most available pattern recognition methods in neuroimaging address binary classification problems. Here, we used relevance vector machine (RVM) in combination with booststrap resampling (‘bagging’) for non-hierarchical multiclass classification. The method was tested on 120 cerebral 18fluorodeoxyglucose (FDG) positron emission tomography (PET) scans performed in patients who exhibited parkinsonian clinical features for 3.5 years on average but that were outside the prevailing perception for Parkinson's disease (PD). A radiological diagnosis of PD was suggested for 30 patients at the time of PET imaging. However, at follow-up several years after PET imaging, 42 of them finally received a clinical diagnosis of PD. The remaining 78 APS patients were diagnosed with multiple system atrophy (MSA, N = 31), progressive supranuclear palsy (PSP, N = 26) and corticobasal syndrome (CBS, N = 21), respectively. With respect to this standard of truth, classification sensitivity, specificity, positive and negative predictive values for PD were 93% 83% 75% and 96%, respectively using binary RVM (PD vs. APS) and 90%, 87%, 79% and 94%, respectively, using multiclass RVM (PD vs. MSA vs. PSP vs. CBS). Multiclass RVM achieved 45%, 55% and 62% classification accuracy for, MSA, PSP and CBS, respectively. Finally, a majority confidence ratio was computed for each scan on the basis of class pairs that were the most frequently assigned by RVM. Altogether, the results suggest that automatic multiclass RVM classification of FDG PET scans achieves adequate performance for the early differentiation between PD and APS on the basis of cerebral FDG uptake patterns when the clinical diagnosis is felt uncertain. This approach cannot be recommended yet as an aid for distinction between the three APS classes under consideration. [less ▲]

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See detailConcurrent Synaptic and Systems Memory Consolidation during Sleep
Mascetti, Laura; Foret, Ariane; Schrouff, Jessica ULg et al

in Journal of Neuroscience (2013), 33(24), 10182-10190

Memories are consolidated during sleep by two apparently antagonistic processes: (1) reinforcement of memory-specific cortical interactions and (2) homeostatic reduction in synaptic efficiency. Using fMRI ... [more ▼]

Memories are consolidated during sleep by two apparently antagonistic processes: (1) reinforcement of memory-specific cortical interactions and (2) homeostatic reduction in synaptic efficiency. Using fMRI, we assessed whether episodic memories are processed during sleep by either or both mechanisms, by comparing recollection before and after sleep. We probed whether LTP influences these processes by contrasting two groups of individuals prospectively recruited based on BDNF rs6265 (Val66Met) polymorphism. Between immediate retrieval and delayed testing scheduled after sleep, responses to recollection increased significantly more in Val/Val individuals than in Met carriers in parietal and occipital areas not previously engaged in retrieval, consistent with “systems-level consolidation.” Responses also increased differentially between allelic groups in regions already activated before sleep but only in proportion to slow oscillation power, in keeping with “synaptic downscaling.” Episodic memories seem processed at both synaptic and systemic levels during sleep by mechanisms involving LTP. [less ▲]

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See detailInteraction between hippocampal and striatal systems predicts subsequent consolidation of motor sequence memory.
Albouy, Geneviève; Sterpenich, Virginie; Vandewalle, Gilles ULg et al

in PLoS ONE (2013), 8(3), 59490

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See detailSleep stabilizes visuomotor adaptation memory: a functional magnetic resonance imaging study
Albouy, Geneviève ULg; Vandewalle, Gilles ULg; Sterpenich, Virginie et al

in Journal of Sleep Research (2013), 22(2), 144-54

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See detailEpisodic autobiographical memory in amnestic Mild Cognitive Impairment: What are the neural correlates?
Bastin, Christine ULg; Feyers, Dorothée ULg; Jedidi, Haroun ULg et al

in Human Brain Mapping (2013), 34

Autobiographical memory in amnestic Mild Cognitive Impairment (aMCI) is characterized by impaired retrieval of episodic memories, but relatively preserved personal semantic knowledge. This study aimed to ... [more ▼]

Autobiographical memory in amnestic Mild Cognitive Impairment (aMCI) is characterized by impaired retrieval of episodic memories, but relatively preserved personal semantic knowledge. This study aimed to identify (via FDG-PET) the neural substrates of impaired episodic specificity of autobiographical memories in 35 aMCI patients compared with 24 healthy elderly controls. Significant correlations between regional cerebral activity and the proportion of episodic details in autobiographical memories from two life periods were found in specific regions of an autobiographical brain network. In aMCI patients, more than in controls, specifically episodic memories from early adulthood were associated with metabolic activity in the cuneus and in parietal regions. We hypothesized that variable retrieval of episodic autobiographical memories in our aMCI patients would be related to their variable capacity to reactivate specific sensory-perceptual and contextual details of early adulthood events linked to reduced (occipito-parietal) visual imagery and less efficient (parietal) attentional processes. For recent memories (last year), a correlation emerged between the proportion of episodic details and activity in lateral temporal regions and the temporo-parietal junction. Accordingly, variable episodic memory for recent events may be related to the efficiency of controlled search through general events likely to provide cues for the retrieval of episodic details and to the ability to establish a self perspective favouring recollection. [less ▲]

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See detailExploration of the mechanisms underlying the ISPC effect: Evidence from behavioral and neuroimaging data
Grandjean, Julien; D'Ostilio, Kevin ULg; Fias, Wim et al

in Neuropsychologia (2013), 51

The item-specific proportion congruent (ISPC) effect in a Stroop task – the observation of reduced interference for color words mostly presented in an incongruent color – has attracted growing interest ... [more ▼]

The item-specific proportion congruent (ISPC) effect in a Stroop task – the observation of reduced interference for color words mostly presented in an incongruent color – has attracted growing interest since the original study by Jacoby (2003). Two mechanisms have been proposed to explain the effect: associative learning of contingencies and item-specific control through word reading modulation. Both interpretations have received empirical support from behavioral data. Therefore, the aim of this study was to investigate the responsible mechanisms of the ISPC effect with the classic two-item sets design using fMRI. Results showed that the ISPC effect is associated with increased activity in the anterior cingulate (ACC), dorsolateral prefrontal (DLPFC), and inferior and superior parietal cortex. Importantly, behavioral and fMRI analyses specifically addressing the respective contribution of associative learning and item-specific control mechanisms brought support for the contingency learning account of the ISPC effect. Results are discussed in reference to task and procedure characteristics that may influence the extent to which item-specific control and/or contingency learning contribute to the ISPC effect. [less ▲]

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See detailThe impact of visual perceptual learning on sleep and local slow wave initiation
Mascetti, Laura ULg; Muto, Vincenzo ULg; Matarazzo, Luca et al

in Journal of Neuroscience (2013)

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See detailSmall animal imaging with human PET
Bahri, Mohamed Ali ULg; Tombuloglu, S; Warnock, Geoffrey ULg et al

Poster (2012, September)

PET studies provide valuable information in the assessment of animal models for human diseases. MicroPET systems provide the high resolution needed to explore small organs but suffer from a reduced axial ... [more ▼]

PET studies provide valuable information in the assessment of animal models for human diseases. MicroPET systems provide the high resolution needed to explore small organs but suffer from a reduced axial FOV. Multiple bed positions are then used to obtain whole body scans resulting in increased scan time and incomplete dynamic data. In contrast, human PET systems have larger axial FOV but a lower resolution. In this study, an image-based model of the scanner spatial response function combined with a 3D-OSEM reconstruction algorithm were used to improve spatial resolution of the Siemens ECAT EXACT HR+ PET scanner. A stationary double Gaussian model [1] of the ECAT EXACT HR+ point spread function was derived from 18F point source measurements performed at different radial and axial locations in the scanner FOV. This model was used in a 3D-OSEM reconstruction (3D-OSEM-RM). Sinograms were normalized and attenuation and scatter corrected using the Siemens ECAT tools before reconstruction. Both NEMA NU 2-1994 performance phantoms and NEMA NU4-2008 image quality phantom mimicking small animals were used to evaluate the accuracy of corrections for physical effects and the overall image quality. A 50 min dynamic FDG rat study was conducted on the ECAT HR+ and reconstructed with 3D-OSEM-RM. The images were used to compute the metabolic rate of glucose (MRglu) in multiple brain structures. These images were also visually compared to the static image obtained with a FOCUS 120 microPET immediately after the HR+ dynamic scan. The standard deviations of the two Gaussians used to model the transaxial (axial) resolution in a central FOV of 5 cm radius were σ1 = 1.6 (2.75) mm and σ2 = 3.66 (4.16) mm, and the ratio of the weights between the first and second Gaussians was ρ = 0.2 (0.7). Image uniformity and accuracy of scatter and attenuation corrections, evaluated following NEMA NU 2-1994, were found to be very similar between 3D-OSEM, 3D-OSEM-RM, 2D- and 3D-FBP reconstructed images. When using the NEMA NU4-2008 image quality phantom a significant increase of the hot rod recovery coefficient was observed. This effect was rod size dependent and amounted to 17-35% for the 3D-OSEM-RM compared to the 3D-OSEM and to 35-62% compared to the FBP reconstructions. Nevertheless the values obtained with 3D-OSEM-RM were around 20-35% lower than those obtained with the FOCUS 120 microPET scanner. Most of the small brain structures observed on microPET images were also visible on the images obtained with the HR+ scanner and 3D-OSEM-RM. Rat cerebral MRglu values calculated on 3D-OSEM-RM images were in the range of published values [2] (e.g. whole brain = 25.34 μmol/min/100g). Using an approximate model of the ECAT EXACT HR+ spatial response in 3D-OSEM resulted in sufficient image quality for dynamic whole body scans of small rodents, despite the large FOV, and resulted in improved contrast compared to images generated using the built-in software. This methodology will be applied for future small animal dosimetry and modeling studies in our laboratory. [1] Comtat et al. IEEE Nucl Sci Symp Conf Record. pp. 4120-4123 (2008) [2] Schiffer et al. J Nucl Med 48:277-287 (2007) [less ▲]

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See detailNeural Correlates of Performance Variabilty during Motor Sequence Acquisition
Albouy, Geneviève ULg; Sterpenich, V.; Vandewalle, Gilles ULg et al

in NeuroImage (2012), 60(1), 324-331

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See detailInfluence of acute sleep loss on the neural correlates of alerting, orientating and executive attention components
Muto, Vincenzo ULg; Shaffii, Anahita ULg; Matarazzo, Luca et al

in Journal of Sleep Research (2012), 21(6), 648-58

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See detailCircadian preference modulates the neural substrate of conflict processing across the day
Schmidt, Christina ULg; Peigneux, Philippe ULg; Leclercq, Yves ULg et al

in PLoS ONE (2012), 7(1), 29658

Human morning and evening chronotypes differ in their preferred timing for sleep and wakefulness, as well as in optimal daytime periods to cope with cognitive challenges. Recent evidence suggests that ... [more ▼]

Human morning and evening chronotypes differ in their preferred timing for sleep and wakefulness, as well as in optimal daytime periods to cope with cognitive challenges. Recent evidence suggests that these preferences are not a simple by-product of socio-professional timing constraints, but can be driven by inter-individual differences in the expression of circadian and homeostatic sleep-wake promoting signals. Chronotypes thus constitute a unique tool to access the interplay between those processes under normally entrained day-night conditions, and to investigate how they impinge onto higher cognitive control processes. Using functional magnetic resonance imaging (fMRI), we assessed the influence of chronotype and time-of-day on conflict processing-related cerebral activity throughout a normal waking day. Sixteen morning and 15 evening types were recorded at two individually adapted time points (1.5 versus 10.5 hours spent awake) while performing the Stroop paradigm. Results show that interference-related hemodynamic responses are maintained or even increased in evening types from the subjective morning to the subjective evening in a set of brain areas playing a pivotal role in successful inhibitory functioning, whereas they decreased in morning types under the same conditions. Furthermore, during the evening hours, activity in a posterior hypothalamic region putatively involved in sleep-wake regulation correlated in a chronotype-specific manner with slow wave activity at the beginning of the night, an index of accumulated homeostatic sleep pressure. These results shed light into the cerebral mechanisms underlying inter-individual differences of higher-order cognitive state maintenance under normally entrained day-night conditions. [less ▲]

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See detailThe fate of incoming stimuli during NREM sleep is determined by spindles and the phase of the slow oscillation
Schabus, M.; Dang Vu, Thien Thanh ULg; Heib, D. P. J. et al

in Frontiers in Neurology (2012), 3(40), 1-11

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See detailThe Neural Substrates of Memory Suppression: A fMRI Exploration of Directed Forgetting
Bastin, Christine ULg; Feyers, Dorothée ULg; Majerus, Steve ULg et al

in PLoS ONE (2012), 7(1), 29905

The directed forgetting paradigm is frequently used to determine the ability to voluntarily suppress information. However, little is known about brain areas associated with information to forget. The ... [more ▼]

The directed forgetting paradigm is frequently used to determine the ability to voluntarily suppress information. However, little is known about brain areas associated with information to forget. The present study used functional magnetic resonance imaging to determine brain activity during the encoding and retrieval phases of an item-method directed forgetting recognition task with neutral verbal material in order to apprehend all processing stages that information to forget and to remember undergoes. We hypothesized that regions supporting few selective processes, namely recollection and familiarity memory processes, working memory, inhibitory and selection processes should be differentially activated during the processing of to-be-remembered and to-be-forgotten items. Successful encoding and retrieval of items to remember engaged the entorhinal cortex, the hippocampus, the anterior medial prefrontal cortex, the left inferior parietal cortex, the posterior cingulate cortex and the precuneus; this set of regions is well known to support deep and associative encoding and retrieval processes in episodic memory. For items to forget, encoding was associated with higher activation in the right middle frontal and posterior parietal cortex, regions known to intervene in attentional control. Items to forget but nevertheless correctly recognized at retrieval yielded activation in the dorsomedial thalamus, associated with familiarity-based memory processes and in the posterior intraparietal sulcus and the anterior cingulate cortex, involved in attentional processes. [less ▲]

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See detailModulation of brain activity during a Stroop inhibitory task by the kind of cognitive control required
Grandjean, Julien ULg; D'Ostilio, Kevin ULg; Phillips, Christophe ULg et al

in PLoS ONE (2012), 7(7), 41513

This study used a proportion congruency manipulation in the Stroop task in order to investigate, at the behavioral and brain substrate levels, the predictions derived from the Dual Mechanisms of Control ... [more ▼]

This study used a proportion congruency manipulation in the Stroop task in order to investigate, at the behavioral and brain substrate levels, the predictions derived from the Dual Mechanisms of Control (DMC) account of two distinct modes of cognitive control depending on the task context. Three experimental conditions were created that varied the proportion congruency: mostly incongruent (MI), mostly congruent (MC), and mostly neutral (MN) contexts. A reactive control strategy, which corresponds to transient interference resolution processes after conflict detection, was expected for the rare conflicting stimuli in the MC context, and a proactive strategy, characterized by a sustained task-relevant focus prior to the occurrence of conflict, was expected in the MI context. Results at the behavioral level supported the proactive/reactive distinction, with the replication of the classic proportion congruent effect (i.e., less interference and facilitation effects in the MI context). fMRI data only partially supported our predictions. Whereas reactive control for incongruent trials in the MC context engaged the expected fronto-parietal network including dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex, proactive control in the MI context was not associated with any sustained lateral prefrontal cortex activations, contrary to our hypothesis. Surprisingly, incongruent trials in the MI context elicited transient activation in common with incongruent trials in the MC context, especially in DLPFC, superior parietal lobe, and insula. This lack of sustained activity in MI is discussed in reference to the possible involvement of item-specific rather than list-wide mechanisms of control in the implementation of a high task-relevant focus. [less ▲]

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See detailAttention Supports Verbal Short-Term Memory via Competition between Dorsal and Ventral Attention Networks.
Majerus, Steve ULg; Attout, Lucie ULg; D'Argembeau, Arnaud ULg et al

in Cerebral Cortex (2012), 22

Interactions between the neural correlates of short-term memory (STM) and attention have been actively studied in the visual STM domain but much less in the verbal STM domain. Here we show that the same ... [more ▼]

Interactions between the neural correlates of short-term memory (STM) and attention have been actively studied in the visual STM domain but much less in the verbal STM domain. Here we show that the same attention mechanisms that have been shown to shape the neural networks of visual STM also shape those of verbal STM. Based on previous research in visual STM, we contrasted the involvement of a dorsal attention network centered on the intraparietal sulcus supporting task-related attention and a ventral attention network centered on the temporoparietal junction supporting stimulus-related attention. We observed that, with increasing STM load, the dorsal attention network was activated while the ventral attention network was deactivated, especially during early maintenance. Importantly, activation in the ventral attention network increased in response to task-irrelevant stimuli briefly presented during the maintenance phase of the STM trials but only during low-load STM conditions, which were associated with the lowest levels of activity in the dorsal attention network during encoding and early maintenance. By demonstrating a trade-off between task-related and stimulus-related attention networks during verbal STM, this study highlights the dynamics of attentional processes involved in verbal STM. [less ▲]

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See detailFrontal and posterior cingulate metabolic impairment in the behavioural variant of frontotemporal dementia with impaired autonoetic consciousness
Bastin, Christine ULg; Feyers, Dorothée ULg; Souchay, Céline et al

in Human Brain Mapping (2012), 33

Although memory dysfunction is not a prominent feature of the behavioural variant of frontotemporal dementia (bv-FTD), there is evidence of specific deficits of episodic memory in these patients. They ... [more ▼]

Although memory dysfunction is not a prominent feature of the behavioural variant of frontotemporal dementia (bv-FTD), there is evidence of specific deficits of episodic memory in these patients. They also have problems monitoring their memory performance. The objective of the present study was to explore the ability to consciously retrieve own encoding of the context of events (autonoetic consciousness) and the ability to monitor memory performance using feeling-of-knowing (FOK) in bv-FTD. Analyses of the patients’ cerebral metabolism (FDG-PET) allowed an examination of whether impaired episodic memory in bv-FTD is associated with the frontal dysfunction characteristic of the pathology or a dysfunction of memory-specific regions pertaining to Papez’s circuit. Data were obtained from 8 bv-FTD patients and 26 healthy controls. Autonoetic consciousness was evaluated by Remember responses during the recognition memory phase of the FOK experiment. As a group, bv-FTD patients demonstrated a decline in autonoetic consciousness and FOK accuracy at the chance level. While memory monitoring was impaired in most (7) patients, 4 bv-FTD participants had individual impairment of autonoetic consciousness. They specifically showed reduced metabolism in the anterior medial prefrontal cortex, the left dorsolateral prefrontal cortex (near the superior frontal sulcus), parietal regions and the posterior cingulate cortex. These findings were tentatively interpreted by considering the role of the metabolically impaired brain regions in self-referential processes, suggesting that the bv-FTD patients’ problem consciously retrieving episodic memories may stem at least partly from deficient access to and maintenance/use of information about the self. [less ▲]

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See detailBrain energization in response to deep brain stimulation of subthalamic nuclei in Parkinson's disease.
Garraux, Gaëtan ULg; Bahri, Mohamed Ali ULg; Lemaire, Christian ULg et al

in Journal of Cerebral Blood Flow & Metabolism (2011)

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment in a subgroup of medically refractory patients with Parkinson's disease (PD). Here, we compared resting-state (18)F ... [more ▼]

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment in a subgroup of medically refractory patients with Parkinson's disease (PD). Here, we compared resting-state (18)F-fluorodeoxyglucose (FDG) positron emission tomography images in the stimulator off (DBS_OFF) and on (DBS_ON) conditions in eight PD patients in an unmedicated state, on average 2 years after bilateral electrode implantation. Global standardized uptake value (SUV) significantly increased by approximately 11% in response to STN-DBS. To avoid any bias in the voxel-based analysis comparing DBS_ON and DBS_OFF conditions, individual scan intensity was scaled to a region where FDG-SUV did not differ significantly between conditions. The resulting FDG-SUV ratio (FDG-SUVR) was found to increase in many regions in response to STN-DBS including the target area of surgery, caudate nuclei, primary sensorimotor, and associative cortices. Contrary to previous studies, we could not find any regional decrease in FDG-SUVR. These findings were indirectly supported by comparing the extent of areas with depressed FDG-SUVR in DBS_OFF and DBS_ON relatively to 10 normal controls. Altogether, these novel results support the prediction that the effect of STN-DBS on brain activity in PD is unidirectional and consists in an increase in many subcortical and cortical regions.Journal of Cerebral Blood Flow & Metabolism advance online publication, 6 April 2011; doi:10.1038/jcbfm.2011.41. [less ▲]

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