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Biomedical subjects

D Rivière

Publications and source records attributed to D Rivière.

At least 19 recordsLinked to original sources
PubMed2005

Modulation of language areas with functional MR image-guided magnetic stimulation.

Repetitive transcranial magnetic stimulation (rTMS) can interfere with linguistic performance when delivered over language areas. At low frequency (1 Hz), rTMS is assumed to decrease cortical excitability; however, the degree of TMS effect on cortical language areas may depend on the localization of the stimulation coil with respect to the inter-individual anatomo-functional variations. Hence, we aimed at investigating individual brain areas involved in semantic and phonological auditory processes. We hypothesized that active rTMS targeted over Wernicke's area might modify the performance during a language-fragment-detection task. Sentences in native or foreign languages were presented to 12 right-handed male healthy volunteers during functional magnetic resonance imaging (fMRI). 3D-functional maps localized the posterior temporal activation (Wernicke) in each subject and MRI anatomical cortical landmarks were used to define Broca's pars opercularis (F3Op). A frameless stereotaxy system was used to guide the TMS coil position over Wernicke's and F3Op areas in each subject. Active and placebo randomized rTMS sessions were applied at 1 Hz, 110% of motor threshold, during the same language-fragment-detection task. Accuracy and response time (RT) were recorded. RT was significantly decreased by active rTMS compared to placebo over Wernicke's area, and was more decreased for native than for foreign languages. No significant RT change was observed for F3Op area. rTMS conditions did not impair participants' accuracy. Thus, low-frequency rTMS over Wernicke's area can speed-up the response to a task tapping on native language perception in healthy volunteers. This individually-guided stimulation study confirms that facilitatory effects are not confined to high-frequency rTMS.

Adult↗
PubMed2005

MR diffusion-based inference of a fiber bundle model from a population of subjects.

This paper proposes a method to infer a high level model of the white matter organization from a population of subjects using MR diffusion imaging. This method takes as input for each subject a set of trajectories stemming from any tracking algorithm. Then the inference results from two nested clustering stages. The first clustering converts each individual set of trajectories into a set of bundles supposed to represent large white matter pathways. The second clustering matches these bundles across subjects in order to provide a list of candidates for the bundle model. The method is applied on a population of eleven subjects and leads to the inference of 17 such candidates.

Algorithms↗
PubMed2005

Anatomically constrained surface parameterization for cortical localization.

We present here a method that aims at defining a surface-based coordinate system on the cortical surface. Such a system is needed for both cortical localization and intersubject matching in the framework of neuroimaging. We propose an automatic parameterization based on the spherical topology of the grey/white matter interface of each hemisphere and on the use of naturally organized and reproducible anatomical features. From those markers used as initial constraints, the coordinate system is propagated via a PDE solved on the cortical surface.

Algorithms↗
PubMed2004

Brain morphometry using 3D moment invariants.

This paper advocates the use of shape descriptors based on moments of 3D coordinates for morphometry of the cortical sulci. These descriptors, which have been introduced more than a decade ago, are invariant relatively to rotations, translations and scale and can be computed for any topology. A rapid insight into the derivation of these invariants is proposed first. Then, their potential to characterize shapes is shown from a principal component analysis of the 12 first invariants computed for 12 different deep brain structures manually drawn for 7 different brains. Finally, these invariants are used to find some correlates of handedness and sex among the shapes of 116 different cortical sulci automatically identified in each of 142 brains of the ICBM database.

Algorithms↗
PubMed2004

A framework to study the cortical folding patterns.

This paper describes a decade-long research program focused on the variability of the cortical folding patterns. The program has developed a framework of using artificial neuroanatomists that are trained to identify sulci from a database. The framework relies on a renormalization of the brain warping problem, which consists in matching the cortices at the scale of the folds. Another component of the program is the search for the alphabet of the folding patterns, namely, a list of indivisible elementary sulci. The search relies on the study of the cortical folding process using antenatal imaging and on backward simulations of morphogenesis aimed at revealing traces of the embryologic dimples in the mature cortical surface. The importance of sulcal-based morphometry is illustrated by a simple study of the correlates of handedness on asymmetry indices. The study shows for instance that the central sulcus is larger in the dominant hemisphere.

Brain Mapping↗
PubMed2004

Coordinate-based versus structural approaches to brain image analysis.

A basic issue in neurosciences is to look for possible relationships between brain architecture and cognitive models. The lack of architectural information in magnetic resonance images, however, has led the neuroimaging community to develop brain mapping strategies based on various coordinate systems without accurate architectural content. Therefore, the relationships between architectural and functional brain organizations are difficult to study when analyzing neuroimaging experiments. This paper advocates that the design of new brain image analysis methods inspired by the structural strategies often used in computer vision may provide better ways to address these relationships. The key point underlying this new framework is the conversion of the raw images into structural representations before analysis. These representations are made up of data-driven elementary features like activated clusters, cortical folds or fiber bundles. Two classes of methods are introduced. Inference of structural models via matching across a set of individuals is described first. This inference problem is illustrated by the group analysis of functional statistical parametric maps (SPMs). Then, the matching of new individual data with a priori known structural models is described, using the recognition of the cortical sulci as a prototypical example.

Brain↗
PubMed2004

Effects of brisk walking on static and dynamic balance, locomotion, body composition, and aerobic capacity in ageing healthy active men.

This work analyses the short-term physiological and neurophysiological effects of a brisk walking programme in ageing, healthy, active men. Twenty-one men 63 to 72 years of age were recruited and separated into 2 groups. One group performed a walking programme (WP) (n = 11) and another served as control (C) group (n = 10). The walking programme lasted for twelve weeks and included five sessions per week. Several parameters were assessed before and after the programme for the WP group. The same tests were performed (separated by twelve weeks) in group C. During each assessment, the subjects were put through static and dynamic balance tests, spatio-temporal gait analysis, body composition measurements and determination of aerobic capacity and bone mineral density. The statistic analysis showed a significant improvement in dynamic balance performance, especially in lateral sway when the subjects kept their eyes open, an increase of VO(2) max and loss of fat mass in the WP group. However, no alterations appeared in spatiotemporal gait characteristics, static balance performance, lean mass or bone mineral density (total body and hip). According to these results, this walking programme may have positive effects on preventing ageing subjects from falling.

Accidental Falls↗
PubMed2004

Object-based morphometry of the cerebral cortex.

Most of the approaches dedicated to automatic morphometry rely on a point-by-point strategy based on warping each brain toward a reference coordinate system. In this paper, we describe an alternative object-based strategy dedicated to the cortex. This strategy relies on an artificial neuroanatomist performing automatic recognition of the main cortical sulci and parcellation of the cortical surface into gyral patches. A set of shape descriptors, which can be compared across subjects, is then attached to the sulcus and gyrus related objects segmented by this process. The framework is used to perform a study of 142 brains of the International Consortium for Brain Mapping (ICBM) database. This study reveals some correlates of handedness on the size of the sulci located in motor areas, which was not detected previously using standard voxel based morphometry.

Algorithms↗
PubMed2003

Object-based strategy for morphometry of the cerebral cortex.

Most of the approaches dedicated to automatic morphometry rely on a point-by-point strategy based on warping each brain towards a reference coordinate system. In this paper, we describe an alternative object-based strategy dedicated to the cortex. This strategy relies on an artificial neuroanatomist performing automatic recognition of the main cortical sulci and parcellation of the cortical surface into gyral patches. A set of shape descriptors, which can be compared across subjects, is then attached to the sulcus and gyrus related objects segmented by this process. The framework is used to perform a study of 142 brains of the ICBM database. This study reveals some correlates of handedness on the size of the sulci located in motor areas, which seem to be beyond the scope of the standard voxel based morphometry.

Algorithms↗
PubMed2003

A generic framework for the parcellation of the cortical surface into gyri using geodesic Voronoï diagrams.

In this paper we propose a generic automatic approach for the parcellation of the cortical surface into labeled gyri. These gyri are defined from a set of pairs of sulci selected by the user. The selected sulci are first automatically identified in the data, then projected onto the cortical surface. The parcellation stems from two nested Voronoï diagrams computed geodesically to the cortical surface. The first diagram provides the zones of influence of the sulci. The boundary between the two zones of influence of each selected pair of sulci stands for a gyrus seed. A second diagram yields the gyrus parcellation. The distance underlying the Voronoï diagram allows the method to interpolate the gyrus boundaries where the limiting sulci are interrupted. The method is illustrated with 12 different hemispheres.

Automation↗
PubMed2003

Post-exercise increase of lipid oxidation after a moderate exercise bout in untrained healthy obese men.

The aim of the study was to examine whether a moderate exercise increases the utilization of fatty acids during the recovery period in obese men. Six healthy obese participated in a randomized crossover investigation, one with exercise and one without exercise. At 8 a. m., the subjects had a standardized breakfast and they rested in a sitting position for 3 hours. The subjects were maintained in the sitting position for 4 additional hours in one session. In a second session, they exercised for 60 min at 50 % of their VO(2) max and then returned to the sitting position for 3 hours. Respiratory exchange ratio (RER) values were calculated by indirect calorimetry. During the resting session, plasma non-esterified fatty acids (NEFA) and glycerol concentrations rose progressively, whereas RER progressively decreased. During the exercise, plasma catecholamines, NEFA, glycerol, growth hormone and cortisol levels and RER increased while insulin decreased. During the recovery, plasma NEFA increased and glycerol decreased. During the first hour of recovery, RER values were lower and fatty acid utilization higher than during the same period of the resting session. The study shows that exercise induces modifications in hormonal factors promoting lipid mobilization and suggests that exercise provide substantial amounts of NEFA for muscle oxidation during recovery from an exercise bout in obese subjects.

Adult↗
PubMed2003

A primal sketch of the cortex mean curvature: a morphogenesis based approach to study the variability of the folding patterns.

In this paper, we propose a new representation of the cortical surface that may be used to study the cortex folding process and to recover some putative stable anatomical landmarks called sulcal roots usually buried in the depth of adult brains. This representation is a primal sketch derived from a scale space computed for the mean curvature of the cortical surface. This scale-space stems from a diffusion equation geodesic to the cortical surface. The primal sketch is made up of objects defined from mean curvature minima and saddle points. The resulting sketch aims first at highlighting significant elementary cortical folds, second at representing the fold merging process during brain growth. The relevance of the framework is illustrated by the study of central sulcus sulcal roots from antenatal to adult age. Some results are proposed for ten different brains. Some preliminary results are also provided for superior temporal sulcus.

Adult↗
PubMed2003

Aerobic training improves exercise-induced lipolysis in SCAT and lipid utilization in overweight men.

The aim of this study was to investigate whether endurance training improves lipid mobilization and oxidation in overweight subjects. Eleven young men (25.6 +/- 1.4 yr and body mass index 27.7 +/- 0.2) performed a 4-mo training program consisting of practicing aerobic exercise 5 days/wk. Before and after the training period, lipid oxidation was explored during a 60-min exercise at 50% of peak O2 consumption by use of indirect calorimetry. Lipid mobilization and antilipolytic alpha2-adrenoceptor effect were also studied using the microdialysis method in abdominal subcutaneous adipose tissue (SCAT). After training, plasma nonesterified fatty acid (NEFA) levels, at rest and during exercise, were significantly lower than before (P < 0.001). Lipolysis in SCAT was significantly higher after than before training. An antilipolytic alpha2-adrenoceptor effect in SCAT was underlined during exercise before training and disappeared after. The respiratory exchange ratio was lower after training, i.e., the percentage of lipid oxidation was higher only at rest. The amount of lipid oxidized was higher after training, at rest, and during exercise. Although exercise power was higher after training, the relative intensity was equivalent, as suggested by a similar increase in plasma catecholamine concentrations before and after training. In conclusion, 4-mo training in overweight men improved lipid mobilization through a decrease of antilipolytic alpha2-adrenoceptor effect in SCAT and lipid oxidation during moderate exercise. Training induced a decrease of blood NEFA, predicting better prevention of obesity.

Abdomen↗
PubMed2003

[Sport and atopy].

INTRODUCTION: The atopic diseases, asthma, allergic rhinitis and atopic dermatitis, are common in children, adolescents and young adults. They may have important consequences on physical exercise, especially asthma. STATE OF ART: Elite athletes have been observed to have a high prevalence of asthma (and perhaps also rhinitis). The reasons for this observation are still debated, but different mechanisms linked to the intensity of physical activity in athletes are probably involved. Exercise-induced symptoms should be confirmed not only from the clinical history but also by objective measurements of lung function. In elite athletes confirmation of exercise-induced asthma might be difficult and may require special diagnostic tests such as bronchial provocation by eucapnic voluntary hyperventilation. Several drugs are effective in exercise-induced prevention of nasal and bronchial symptoms. Therapeutic approaches for atopic diseases in international guidelines (GINA and ARIA) are generally compatible with anti-doping laws but require compliance with specific prescription rules. PERSPECTIVES: A better understanding of mechanisms and risk factors involved in the increase of asthma prevalence in elite athletes may permit prevention by modifying training conditions during exercise. CONCLUSIONS: Atopic diseases are common in athletes. They require special therapeutic considerations. The increasing prevalence of respiratory asthma-like symptoms in elite athlete is opening new paths for research into airway physiology in extreme conditions.

Adolescent↗
PubMed2002

Effect of a long-duration physical exercise on fat cell lipolytic responsiveness to adrenergic agents and insulin in obese men.

OBJECTIVE: The aim of the study was to investigate whether a long-lasting bout of exercise modifies the lipolytic beta- and antilipolytic-alpha(2)-adrenergic effect and the antilipolytic effect of insulin in obese subjects. DESIGN: Biopsies of abdominal subcutaneous adipose tissue were performed before and immediately after 2 h exercise (at 50% of VO(2max)) on an ergometric bicycle. SUBJECTS: Nine healthy obese male subjects (mean age 38.0+/-3.5 y; mean body mass index (BMI) 35.6+/-3.9 kg/m(2)) were included in the experiment. METHODS: :The lipolytic responsiveness to adrenaline, isoprenaline (beta-adrenergic agonist), UK-14304 (alpha(2)-adrenergic agonist) and insulin was studied in the isolated fat cell obtained by biopsies of subcutaneous adipose tissue from the peri-umbilical region before and after exercise. RESULTS: After exercise, an increase was observed in spontaneous lipolytic rate, and in the lipolytic effect of isoprenaline, but no modification in the lipolytic action of adrenaline. Antilipolytic effects of UK-14304 and insulin were not changed by the single bout of exercise. CONCLUSION: A single bout of long-term exercise increased the responsiveness of adipose tissue to beta-adrenergic stimulation of lipolysis in obese subjects.

Abdomen↗
PubMed2001

Modulation of parietal activation by semantic distance in a number comparison task.

The time to compare two numbers shows additive effects of number notation and of semantic distance, suggesting that the comparison task can be decomposed into distinct stages of identification and semantic processing. Using event-related fMRI and high-density ERPs, we isolated cerebral areas where activation was influenced by input notation (verbal or Arabic notation). The bilateral extrastriate cortices and a left precentral region were more activated during verbal than during Arabic stimulation, while the right fusiform gyrus and a set of bilateral inferoparietal and frontal regions were more activated during Arabic than during verbal stimulation. We also identified areas that were influenced solely by the semantic content of the stimuli (numerical distance between numbers to be compared) independent of the input notation. Activation tightly correlated with numerical distance was observed mainly in a group of parietal areas distributed bilaterally along the intraparietal sulci and in the precuneus, as well as in the left middle temporal gyrus and posterior cingulate. Our results support the assumption of a central semantic representation of numerical quantity that relies on a common parietal network shared among notations.

Adult↗
PubMed2001

Cerebral mechanisms of word masking and unconscious repetition priming.

We used functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs) to visualize the cerebral processing of unseen masked words. Within the areas associated with conscious reading, masked words activated left extrastriate, fusiform and precentral areas. Furthermore, masked words reduced the amount of activation evoked by a subsequent conscious presentation of the same word. In the left fusiform gyrus, this repetition suppression phenomenon was independent of whether the prime and target shared the same case, indicating that case-independent information about letter strings was extracted unconsciously. In comparison to an unmasked situation, however, the activation evoked by masked words was drastically reduced and was undetectable in prefrontal and parietal areas, correlating with participants' inability to report the masked words.

Adult↗