| Publications of year 2006 |
| Books |
| Theses |
| Abstract: | L'homme manipule les nombres en utilisant les mots de sa langue. De plus, tout un ensemble de données convergent pour indiquer qu'il dispose aussi d'un système non-verbal pour représenter la numérosité des ensembles, système hérité du monde animal. Nous avons abordé la question des interactions entre représentations numériques verbales et non-verbales, en étudiant trois populations différentes : des adultes occidentaux, des bébés de trois mois, ainsi que des Indiens d'Amazonie, les Mundu! rucus, peuple dont la langue possède un lexique numérique très restreint. Nos recherches s'articulent autour des trois axes suivants : 1. Tout d'abord nous avons cherché à donner une caractérisation fine des représentations non-verbales de la numérosité, à l'aide d'un modèle mathématique, qui postule que les numérosités sont représentées sur un continuum interne, la ligne numérique interne. Les prédictions! du modèle s'accordent avec un ensemble de mesures expérimentales, sur des tâches de comparaison, d'addition et de soustraction de numérosités. Enfin, en confrontant les prédictions du modèle aux résultats d'une tâche d'estimation de numérosité que nous avons développée, nous avons pu conclure que la ligne numérique interne est compressive. 2. Par ailleurs, nos travaux sur l'estimation abordent la question des liens entre les représentations de numérosités et les numéraux de la langue. De manière spontanée, les sujets ont une tendance marquée à sous-estimer la numérosité des stimuli, mais la donnée d'un indice suffit à modifier radicalement la manière dont ils sont calibrés. De plus, le processus de calibration agit de manière globale sur toute la ligne numérique. 3. Enfin, que se passe-t-il en l'absence de représentations verbales pour les nombres ? A l'aide de la technique des potentiels évoqués (ERPs), nous avons montré que les bébés âgés de trois mois sont déjà sensibles à la numérosité. Par ailleurs, nos expériences chez les Indiens Mundurucus montrent qu'en l'absence d'un lexique pour les grands nombres, ceux-ci déploient les mêmes compétences que des occidentaux dans des tâches d'arithmétique sur la numérosité, tant qu'on n'exige qu'une réponse approximative. De plus, les Mundurucus possèdent un concept d'égalité exacte, transcendant leurs représentations non-verbales approximatives de numérosité, mais se trouvent limités dans la plupart des tâches d'arithmétique exacte, de fait qu'il leur manque un outil cognitif (analogue à notre procédure de comptage) pour évaluer! la numérosité exacte d'un ensemble. Ces résultats nous éclairent sur les influences respectives de notre bagage biologique et de la culture dans le développement de la cognition numérique |
| Book chapters |
| Articles in journals |
| Abstract: | The supplementary motor area (SMA) is a key structure for behavioral planning and execution. Recent research on motor control conducted with monkeys and humans has put to light an anatomical and functional distinction between pre-SMA and SMA-proper. According to this view, the pre-SMA would be involved in higher level processes while the SMA-proper would be more closely tied to motor output. We extended this general framework to the verbal domain, in order to investigate the role of the SMA in speech production. We conducted two speech production experiments with fMRI where we manipulated parameters such as familiarity, complexity or constraints on word selection. The results reveal a parcellation of the SMA into three distinct regions, according to their involvement in different aspects of word production. More specifically, following a rostrocaudal gradient, we observed differential activations related to lexical selection, linear sequence encoding and control of motor output. A parallel organization was observed in the dorsolateral frontal cortex. By refining its anatomical and functional parcellation, these results clarify the roles of the SMA in speech production |
| Abstract: | 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 |
| Abstract: | OBJECTIVE: Altered anterior cingulate cortex activity has been consistently detected by functional imaging in schizophrenia patients. In the present study, we hypothesized that the detection of such local hypoactivity varies when the subjects' local gyrification is monitored. Using a group-statistical approach, we investigated whether the presence or absence of a paracingulate sulcus (PCS) does influence the detection of the activation patterns in the cognitive division of the anterior cingulate cortex (ACcd). METHOD: fMRI data were acquired using an event-related paradigm during a task involving both priming and interference between stimuli. In the fMRI dataset collected from 13 schizophrenia patients and 16 healthy subjects, subgroups were defined according to the presence or absence of a PCS. Regional activations during interference between stimuli were examined in the ACcd of each hemisphere, using for each region of interest both voxel-based random-effects and non-parametric analyses. RESULTS: ACcd activation was left-sided in healthy subjects with a PCS, and right-sided in healthy subjects devoid of a PCS. ACcd activations were detected bilaterally in schizophrenia patients with a PCS, whereas left ACcd was deactivated in patients without a PCS. Subgroup comparisons revealed no difference between healthy subjects with a PCS and patients with a PCS, whereas in the subgroups devoid of PCS, the patients exhibited a bilateral ACcd hypoactivation relative to healthy subjects. CONCLUSIONS: PCS presence or absence influences the detection of ACcd activations in group-analysis of schizophrenia patients |
| Abstract: | Previous studies have shown that processing information in one sensory modality can either be enhanced or attenuated by concurrent stimulation of another modality. Here, we reconcile these apparently contradictory results by showing that the sign of cross-modal interactions depends on whether the content of two modalities is associated or not. When concurrently presented auditory and visual stimuli are paired by chance, cue-induced preparatory neural activity is strongly enhanced in the task-relevant sensory system and suppressed in the irrelevant system. Conversely, when information in the two modalities is reliably associated, activity is enhanced in both systems regardless of which modality is task relevant. Our findings illustrate an ecologically optimal flexibility of the neural mechanisms that govern multisensory processing: facilitation occurs when integration is expected, and suppression occurs when distraction is expected. Because thalamic structures were more active when the senses needed to operate separately, we propose them to serve gatekeeper functions in early cross-modal interactions |
| Abstract: | Five experiments investigated whether adults and preschool children can perform simple arithmetic calculations on non-symbolic numerosities. Previous research has demonstrated that human adults, human infants, and non-human animals can process numerical quantities through approximate representations of their magnitudes. Here we consider whether these non-symbolic numerical representations might serve as a building block of uniquely human, learned mathematics. Both adults and children with no training in arithmetic successfully performed approximate arithmetic on large sets of elements. Success at these tasks did not depend on non-numerical continuous quantities, modality-specific quantity information, the adoption of alternative non-arithmetic strategies, or learned symbolic arithmetic knowledge. Abstract numerical quantity representations therefore are computationally functional and may provide a foundation for formal mathematics |
| Abstract: | Of the many brain events evoked by a visual stimulus, which are specifically associated with conscious perception, and which merely reflect non-conscious processing? Several recent neuroimaging studies have contrasted conscious and non-conscious visual processing, but their results appear inconsistent. Some support a correlation of conscious perception with early occipital events, others with late parieto-frontal activity. Here we attempt to make sense of these dissenting results. On the basis of the global neuronal workspace hypothesis, we propose a taxonomy that distinguishes between vigilance and access to conscious report, as well as between subliminal, preconscious and conscious processing. We suggest that these distinctions map onto different neural mechanisms, and that conscious perception is systematically associated with surges of parieto-frontal activity causing top-down amplification |
| Abstract: | Does geometry constitute a core set of intuitions present in all humans, regardless of their language or schooling? We used two nonverbal tests to probe the conceptual primitives of geometry in the Munduruku, an isolated Amazonian indigene group. Munduruku children and adults spontaneously made use of basic geometric concepts such as points, lines, parallelism, or right angles to detect intruders in simple pictures, and they used distance, angle, and sense relationships in geometrical maps to locate hidden objects. Our results provide evidence for geometrical intuitions in the absence of schooling, experience with graphic symbols or maps, or a rich language of geometrical terms |
| Abstract: | Subliminal words cause behavioral priming, yet the depth of their processing remains debated. Using transcranial magnetic stimulation (TMS), Nakamura et al. demonstrate in this issue of Neuron that this subliminal priming effect can be selectively disrupted. Distinct TMS sites disrupt priming in lexical decision and pronunciation tasks, suggesting that task set influences subliminal processing |
| Abstract: | The functional organization of the perisylvian language network was examined using a functional MRI (fMRI) adaptation paradigm with spoken sentences. In Experiment 1, a given sentence was presented every 14.4 s and repeated two, three, or four times in a row. The study of the temporal properties of the BOLD response revealed a temporal gradient along the dorsal-ventral and rostral-caudal directions: From Heschl's gyrus, where the fastest responses were recorded, responses became increasingly slower toward the posterior part of the superior temporal gyrus and toward the temporal poles and the left inferior frontal gyrus, where the slowest responses were observed. Repetition induced a decrease in amplitude and a speeding up of the BOLD response in the superior temporal sulcus (STS), while the most superior temporal regions were not affected. In Experiment 2, small blocks of six sentences were presented in which either the speaker voice or the linguistic content of the sentence, or both, were repeated. Data analyses revealed a clear asymmetry: While two clusters in the left superior temporal sulcus showed identical repetition suppression whether the sentences were produced by the same speaker or different speakers, the homologous right regions were sensitive to sentence repetition only when the speaker voice remained constant. Thus, hemispheric left regions encode linguistic content while homologous right regions encode more details about extralinguistic features like speaker voice. The results demonstrate the feasibility of using sentence-level adaptation to probe the functional organization of cortical language areas. Hum Brain Mapp, 2006. (c) 2006 Wiley-Liss, Inc |
| Abstract: | BACKGROUND: Studies of visual backward masking have frequently revealed an elevated masking threshold in schizophrenia. This finding has frequently been interpreted as indicating a low-level visual deficit. However, more recent models suggest that masking may also involve late and higher-level integrative processes, while leaving intact early bottom-up visual processing. OBJECTIVE: To test the hypothesis that the backward-masking deficit in schizophrenia corresponds to a deficit in the late stages of conscious perception, whereas the subliminal processing of masked stimuli is fully preserved. DESIGN: Twenty-eight patients with schizophrenia and 28 normal control subjects performed 2 backward-masking experiments. We used Arabic digits as stimuli and varied quasi-continuously the interval with a subsequent mask, thus allowing us to progressively unmask the stimuli. We finely quantified their degree of visibility using objective and subjective measures to evaluate the threshold duration for access to consciousness. We also studied the priming effect caused by the variably masked numbers in a comparison task performed on a subsequently presented and highly visible target number. RESULTS: The threshold delay between the digit and mask necessary for the conscious perception of the masked stimulus was longer in patients compared with controls. This higher consciousness threshold in patients was confirmed by an objective and a subjective measure, and both measures were highly correlated for the patients and controls. However, subliminal priming of masked numbers was effective and identical in patients and controls. CONCLUSIONS: Access to conscious report of masked stimuli is impaired in schizophrenia, whereas fast bottom-up processing of the same stimuli, as assessed by subliminal priming, is preserved. These findings suggest a high-level origin of the masking deficit in schizophrenia, although they leave open for further research its exact relation to previously identified bottom-up visual processing abnormalities |
| Abstract: | Mammals acquire much of their sensory information by actively moving their sensory organs. Rats, in particular, scan their surrounding environment with their whiskers. This form of active sensing induces specific patterns of temporal encoding of sensory information, which are based on a conversion of space into time via sensor movement. We investigate the ways in which object location is encoded by the whiskers and decoded by the brain. We recorded from first-order neurons located in the trigeminal ganglion (TG) of anaesthetized rats during epochs of artificial whisking induced by electrical stimulation of the facial motor nerve. We found that TG neurons encode the three positional coordinates with different codes. The horizontal coordinate (along the backward-forward axis) is encoded by two encoding schemes, both relying on the firing times of one type of TG neuron, the 'contact cell'. The radial coordinate (from face outward) is encoded primarily by the firing magnitude of another type of TG neurons, the 'pressure cell'. The vertical coordinate (from ground up) is encoded by the identity of activated neurons. The decoding schemes of at least some of these sensory cues, our data suggest, are also active: cortical representations are generated by a thalamic comparison of cortical expectations with incoming sensory data. |
| Abstract: | The human infant is particularly immature at birth and brain maturation, with the myelination of white matter fibers, is protracted until adulthood. Diffusion tensor imaging offers the possibility to describe non invasively the fascicles spatial organization at an early stage and to follow the cerebral maturation with quantitative parameters that might be correlated with behavioral development. Here, we assessed the feasibility to study the organization and maturation of major white matter bundles in eighteen 1- to 4-month-old healthy infants, using a specific acquisition protocol customized to the immature brain (with 15 orientations of the diffusion gradients and a 700 s mm(-2)b factor). We were able to track most of the main fascicles described at later ages despite the low anisotropy of the infant white matter, using the FACT algorithm. This mapping allows us to propose a new method of quantification based on reconstructed tracts, split between specific regions, which should be more sensitive to specific changes in a bundle than the conventional approach, based on regions-of-interest. We observed variations in fractional anisotropy and mean diffusivity over the considered developmental period in most bundles (corpus callosum, cerebellar peduncles, cortico-spinal tract, spino-thalamic tract, capsules, radiations, longitudinal and uncinate fascicles, cingulum). The results are in good agreement with the known stages of white matter maturation and myelination, and the proposed approach might provide important insights on brain development |
| Abstract: | OBJECT: A method is proposed for generating schemes of diffusion gradient orientations which allow the diffusion tensor to be reconstructed from partial data sets in clinical DT-MRI, should the acquisition be corrupted or terminated before completion because of patient motion. MATERIALS AND METHODS: A general energy-minimization electrostatic model was developed in which the interactions between orientations are weighted according to their temporal order during a |