Y Burnod

Publications (37)94.75 Total impact

• Chapter: Space-time statistical model for functional MRI image sequences

  H. Benali, I. Buvat, J. L. Anton, M. Pélégrini, M. Di Paola, J. Bittoun, Y. Burnod, R. Di Paola
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  ABSTRACT: Changes in cerebral blood oxygenation and flow during activation of human brain can be measured using functional magnetic resonance imaging (fMRI) data acquired during periodic sensory stimulation. Ideally, spatial and temporal correlations in the acquired data should all be taken into account to derive statistical parametric maps (SPM) and to identify significant changes in fMRI signal. This paper proposes a multivariate statistical model for brain activation detection accounting for both the spatial and temporal correlations. This model considers a space-time variant error and a spatial Markov random field process is used to yield an unbiased estimate of the SPM. As the number of pixels is large enough, the asymptotic theory is used to derive a threshold allowing the identification of activated areas in the SPM. The method is illustrated on sensorimotor experiments performed on normal subjects using 1.5T gradient-echo MRI.
  11/2006: pages 285-298;
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  Available from: free.fr

  Article: A hierarchy of associations in hippocampo-cortical systems: cognitive maps and navigation strategies.

  J P Banquet, Ph Gaussier, M Quoy, A Revel, Y Burnod
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  ABSTRACT: In this letter we describe a hippocampo-cortical model of spatial processing and navigation based on a cascade of increasingly complex associative processes that are also relevant for other hippocampal functions such as episodic memory. Associative learning of different types and the related pattern encoding-recognition take place at three successive levels: (1) an object location level, which computes the landmarks from merged multimodal sensory inputs in the parahippocampal cortices; (2) a subject location level, which computes place fields by combination of local views and movement-related information in the entorhinal cortex; and (3) a spatiotemporal level, which computes place transitions from contiguous place fields in the CA3-CA1 region, which form building blocks for learning temporospatial sequences. At the cell population level, superficial entorhinal place cells encode spatial, context-independent maps as landscapes of activity; populations of transition cells in the CA3-CA1 region encode context-dependent maps as sequences of transitions, which form graphs in prefrontal-parietal cortices. The model was tested on a robot moving in a real environment; these tests produced results that could help to interpret biological data. Two different goal-oriented navigation strategies were displayed depending on the type of map used by the system. Thanks to its multilevel, multimodal integration and behavioral implementation, the model suggests functional interpretations for largely unaccounted structural differences between hippocampo-cortical systems. Further, spatiotemporal information, a common denominator shared by several brain structures, could serve as a cognitive processing frame and a functional link, for example, during spatial navigation and episodic memory, as suggested by the applications of the model to other domains, temporal sequence learning and imitation in particular.
  Neural Computation 07/2005; 17(6):1339-84. · 1.88 Impact Factor
• Article: Dynamics of parietofrontal networks underlying visuospatial short-term memory encoding.

  A C Croizé, R Ragot, L Garnero, A Ducorps, M Pélégrini-Issac, K Dauchot, H Benali, Y Burnod
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  ABSTRACT: Brain imaging studies in TEP, functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) have shown that visuospatial short-term memory tasks depend on dorsal parietofrontal networks. Knowing the spatiotemporal dynamics of this network would provide further understanding of the neural bases of the encoding process. We combined magnetoencephalography (MEG) with EEG and fMRI techniques to study this network in a task, in which participants had to judge the symmetry in position of two dots, presented either simultaneously ("immediate comparison") or successively ("memorization" of a first dot and "delayed comparison", after 3 s, with a second dot). With EEG, larger amplitude was observed in the parietocentral P3b component (350-500 ms) in the immediate and "delayed comparisons" than in "memorization" condition, where topography at this time was more anterior and right lateralized. MEG provided a more accurate localization and temporal variations of sources, revealing a strong M4 component at 450 ms in the "memorization" condition, with two sources localized in parietal and right premotor regions. These localizations are consistent with both fMRI foci and EEG cortical current source densities (CSD), but only MEG revealed the strong increase in premotor region at 450 ms related to "memorization". These combined results suggest that EEG P3B and MEG M4 components reflect two different dynamics in parietofrontal networks: the parietocentral P3b indexes a decision mechanism during the immediate and "delayed comparisons", whereas the MEG M4 component, with a larger right premotor source, reflects the encoding process in visuospatial short-term memory.
  NeuroImage 12/2004; 23(3):787-99. · 5.89 Impact Factor
• Conference Proceeding: Spatial representation versus navigation through hippocampal, prefrontal and ganglio-basal loops

  J.P. Banquet, Y. Burnod, P. Gaussier, M. Quoy, A. Revel
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  ABSTRACT: A neural network model of intrahippocampal and hippocampo-cortico-gangliobasal loops allows the robotic implementation of the spatial information contained within cognitive maps in neural space, into temporo-spatial sequences of movements during goal-oriented navigation in outer space. At the representation level, the intrahippocampal loop features place cells in entorhinal cortex and transition cells in CA3-CA1 which constitute, as a population, spatial and contextual maps, respectively. Path integration converges with place cell information in the subiculum. The spatial representation in deep and superficial layers of the entorhinal cortex are dissociated; the unidirectional connections between these two layers close the intrahippocamal loop. The prefrontal cortex, at the junction between representation and implementation, receives from three hippocampal subsystems and stores a global graph-map of an environment and the goal locations on this map. The diffusion of activation from active goals through the graph allows path selection in the motivational limbic prefrontal cortex and planning in the executive lateral part. The top-down output from prefrontal cortex and the bottom-up output from the hippocampus combine onto the accumbens the first stage for the stepwise selection and implementation of the optimal actions in the direction of the goal. Proactive and reactive functioning modes are dissociated.
  Neural Networks, 2004. Proceedings. 2004 IEEE International Joint Conference on; 08/2004
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  Available from: nguyendangbinh.org

  Conference Proceeding: Place cells, maps and navigation strategies: processing steps of the cortico-hippocampal system

  J.P. Banquet, P. Gaussier, M. Quoy, A. Revel, Y. Burnod
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  ABSTRACT: A biologically inspired integrated model of different hippocampal subsystems makes a distinction between place cells (PC) within the entorhinal cortex (EC) (diffuse) or dentate gyrus (segregated), and transition cells (TC) in CA3-CA1 that encode transitions between events. These two types of codes support two kinds of hippocampo-cortical cognitive maps: a context-independent map in the subiculum and EC essentially encodes the spatial layout of the environment thanks to a local dominance of ideothetic movement-related information over allothetic (visual) information, and a task- and temporal context-dependent map based on the TC in CA3-CA1 allows the encoding, in higher-order structures, of maps as graphs resulting from combinations of learned sequences of events. The dominantly spatial and the temporal-task-dependent maps are permanently stored in the parietal cortex and the pre-frontal cortex respectively. On the basis of these two maps, two distinct goal-oriented navigation strategies were designed in experimental robotic paradigms: one based on a (population) vector code of the location-actions pairs to learn and implement to reach the goal, and the other based on linking TC together as conditioning chains that are implemented under the top-down guidance of drives and motivations
  Neural Networks, 2002. IJCNN '02. Proceedings of the 2002 International Joint Conference on; 02/2002
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  Available from: Jean-Claude Dreher

  Article: An integrative theory of the phasic and tonic modes of dopamine modulation in the prefrontal cortex

  J. C. Dreher, Y. Burnod
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  ABSTRACT: This paper presents a model of both tonic and phasic dopamine (DA) effects on maintenance of working memory representations in the prefrontal cortex (PFC). The central hypothesis is that DA modulates the efficacy of inputs to prefrontal pyramidal neurons to prevent interferences for active maintenance. Phasic DA release, due to DA neurons discharges, acts at a short time-scale (a few seconds), while the tonic mode of DA release, independent of DA neurons firing, acts at a long time-scale (a few minutes). The overall effect of DA modulation is modeled as a threshold restricting incoming inputs arriving on PFC neurons. Phasic DA release temporary increases this threshold while tonic DA release progressively increases the basal level of this threshold. Thus, unlike the previous gating theory of phasic DA release, proposing that it facilitates incoming inputs at the time of their arrival, the effect of phasic DA release is supposed to restrict incoming inputs during a period of time after DA neuron discharges. The model links the cellular and behavioral levels during performance of a working memory task. It allows us to understand why a critical range of DA D1 receptors stimulation is required for optimal working memory performance and how D1 receptor agonists (respectively antagonists) increase perseverations (respectively distractability). Finally, the model leads to several testable predictions, including that the PFC regulates DA neurons firing rate to adapt to the delay of the task and that increase in tonic DA release may either improve or decrease performance, depending on the level of DA receptors stimulation at the beginning of the task.
  Neural Netw. 01/2002; 15(4-6):583-602.
• Article: Development of a global motor rating scale for young children (0-4 years) including eye-hand grip coordination.

  L Vaivre-Douret, Y Burnod
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  ABSTRACT: A comparative study of the eight motor rating scales available in Western countries demonstrated methodological differences in the choice of items and standardization. We have developed a global motor rating scale that includes items which measure postural-motor, locomotor (PML) and eye-hand grip coordination (EHGC), and which allows the assessment of an average of motor function level (MFL), PML and EHGC development. Scores obtained were used to define the acquisition of motor age based on the skills completed. The items were selected on the basis of the average age at which the function developed in two populations of healthy full-term French infants, followed from birth to 4 months (n = 60) and from 4 months to 4 years (n = 63). Recent French developmental standards (mean age and standard deviation) of acquisition allow the identification of neuro-psychomotor deviations from normal motor behaviour. This includes both static and dynamic motor coordination sequences. Inter-examiner correlations (n = 3) for 15 randomly selected children indicated a coefficient of 0.90. The scale revealed a sequence in the organization of learned postural-motor, locomotor and eye-hand gripping skills which can contribute to the understanding of brain areas implicated in this maturation process.
  Child Care Health and Development 12/2001; 27(6):515-34. · 1.20 Impact Factor
• Article: Recoding arm position to learn visuomotor transformations.

  P Baraduc, E Guigon, Y Burnod
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  ABSTRACT: There is strong experimental evidence that guiding the arm toward a visual target involves an initial vectorial transformation from direction in visual space to direction in motor space. Constraints on this transformation are imposed (i) by the neural codes for incoming information: the desired movement direction is thought to be signalled by populations of broadly tuned neurons and arm position by populations of monotonically tuned neurons; and (ii) by the properties of outgoing information: the actual movement direction results from the collective action of broadly tuned neurons whose preferred directions rotate with the position of the arm. A neural network model is presented that computes the visuomotor mapping, given these constraints. Appropriate operations are learned by the network in an unsupervised fashion through repeated action- perception cycles by recoding the arm-related proprioceptive information. The resulting solution has two interesting properties: (i) the required transformation is executed accurately over a large part of the reaching space, although few positions are actually learned; and (ii) properties of single neurons and populations in the network closely resemble those of neurons and populations in parietal and motor cortical regions. This model thus suggests a realistic scenario for the calculation of coordinate transformations and initial motor command for arm reaching movements.
  Cerebral Cortex 11/2001; 11(10):906-17. · 6.54 Impact Factor
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  Available from: Marie-Laure Paillère-Martinot

  Article: Temporal order and spatial memory in schizophrenia: a parametric study.

  J C Dreher, J P Banquet, J F Allilaire, M L Paillère-Martinot, B Dubois, Y Burnod
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  ABSTRACT: Spatial working memory has been shown to be impaired in schizophrenia. In contrast, memory for temporal order has been poorly studied in patients with schizophrenia. The aim of this study was to compare and to further characterize spatial working memory and sequence reproduction deficits in patients with schizophrenia under stable medication by manipulating cues (pattern versus sequence), delay, set-size and response type in various recall and recognition tasks. This allowed us to dissociate processes as encoding, retention and retrieval and to compare the performance of patients with schizophrenia to the performance of patients with prefrontal lesions, who have been previously tested in the same tasks. Our results show that increase of the set-size and of the delay decreased performance of both groups, and that these factors had larger detrimental effects in patients with schizophrenia than in controls. Furthermore, comparison between tasks revealed retention and retrieval deficits in schizophrenia. Finally, patients with schizophrenia showed impairments not only in recall but also in sequence recognition tasks with delay. This is in contrast to patients with prefrontal lesions, who have previously been shown to have intact recognition of sequences after a delay. These results suggest that the working memory deficit in schizophrenia cannot be restricted to a prefrontal dysfunction.
  Schizophrenia Research 10/2001; 51(2-3):137-47. · 4.75 Impact Factor
• Conference Proceeding: Sequence learning and timing in hippocampus, prefrontal cortex, and accumbens

  J.P. Banquet, P. Gaussier, A. Revel, S. Moga, Y. Burnod
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  ABSTRACT: A basic architecture inspired from dentate gyrus and CA3-CA1 hippocampal fields combines a spectral timing module and an association network learning event transitions. According to the type of input the system can learn and replay: purely temporal sequences of aperiodic events; place-field chains as building blocks of graphs and maps, by combining visual and path-integration inputs; imitated sequences of movements by combining optic flow and movement-related proprioceptive feedback. The model is part of a triptych featuring also place cell computation and planning. The integrated architecture is used as a control system for robot navigation, sequence learning, prediction and novelty detection
  Neural Networks, 2001. Proceedings. IJCNN '01. International Joint Conference on; 02/2001
• Conference Proceeding: A hippocampal model of visually guided navigation as implemented bya mobile agent

  J P Banquet, P. Gaussier, A. Revel, Y Burnod
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  ABSTRACT: Visually guided landmark navigation is based on space coding by hippocampal place cells (PC). A biologically realistic architecture of cooperative-competitive associative networks (implemented as a control system for mobile agents) emulates PC activity during local navigation in exploration and goal-retrieval. The system builds and stores panoramic views from landmarks and compares them with current inputs. Mismatch-induced low levels of recognition trigger a vigilance burst, which favors either the recognition of an alternative place category or the creation of a new category. The sole implementation of visual “What” and “Where” information does not restrain the generality of the model since several modalities could cooperate to give rise to more robust place field spatial categories. Providing the system with real visual inputs automatically extracted from a natural environment demonstrates that interspecies differences in PC coding result more from characteristics of the visual systems than from differences in processing. Conversely, differences in PC multiple codes within a system result from different levels of processing and/or different degrees of multimodality. Each code could be used within different navigational strategies. A control system derived from the model allows a mobile agent to learn a few places and the associated actions required to reach a goal. Generalisation property of the model provides the capacity to join the goal from any place in the learned environment
  Neural Networks, 2000. IJCNN 2000, Proceedings of the IEEE-INNS-ENNS International Joint Conference on; 02/2000
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  Available from: Etienne Koechlin

  Article: Parieto-frontal coding of reaching: an integrated framework.

  Y Burnod, P Baraduc, A Battaglia-Mayer, E Guigon, E Koechlin, S Ferraina, F Lacquaniti, R Caminiti
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  ABSTRACT: In the last few years, anatomical and physiological studies have provided new insights into the organization of the parieto-frontal network underlying visually guided arm-reaching movements in at least three domains. (1) Network architecture. It has been shown that the different classes of neurons encoding information relevant to reaching are not confined within individual cortical areas, but are common to different areas, which are generally linked by reciprocal association connections. (2) Representation of information. There is evidence suggesting that reach-related populations of neurons do not encode relevant parameters within pure sensory or motor "reference frames", but rather combine them within hybrid dimensions. (3) Visuomotor transformation. It has been proposed that the computation of motor commands for reaching occurs as a simultaneous recruitment of discrete populations of neurons sharing similar properties in different cortical areas, rather than as a serial process from vision to movement, engaging different areas at different times. The goal of this paper was to link experimental (neurophysiological and neuroanatomical) and computational aspects within an integrated framework to illustrate how different neuronal populations in the parieto-frontal network operate a collective and distributed computation for reaching. In this framework, all dynamic (tuning, combinatorial, computational) properties of units are determined by their location relative to three main functional axes of the network, the visual-to-somatic, position-direction, and sensory-motor axis. The visual-to-somatic axis is defined by gradients of activity symmetrical to the central sulcus and distributed over both frontal and parietal cortices. At least four sets of reach-related signals (retinal, gaze, arm position/movement direction, muscle output) are represented along this axis. This architecture defines informational domains where neurons combine different inputs. The position-direction axis is identified by the regular distribution of information over large populations of neurons processing both positional and directional signals (concerning the arm, gaze, visual stimuli, etc.) Therefore, the activity of gaze- and arm-related neurons can represent virtual three-dimensional (3D) pathways for gaze shifts or hand movement. Virtual 3D pathways are thus defined by a combination of directional and positional information. The sensory-motor axis is defined by neurons displaying different temporal relationships with the different reach-related signals, such as target presentation, preparation for intended arm movement, onset of movements, etc. These properties reflect the computation performed by local networks, which are formed by two types of processing units: matching and condition units. Matching units relate different neural representations of virtual 3D pathways for gaze or hand, and can predict motor commands and their sensory consequences. Depending on the units involved, different matching operations can be learned in the network, resulting in the acquisition of different visuo-motor transformations, such as those underlying reaching to foveated targets, reaching to extrafoveal targets, and visual tracking of hand movement trajectory. Condition units link these matching operations to reinforcement contingencies and therefore can shape the collective neural recruitment along the three axes of the network. This will result in a progressive match of retinal, gaze, arm, and muscle signals suitable for moving the hand toward the target.
  Experimental Brain Research 01/2000; 129(3):325-46. · 2.39 Impact Factor
• Article: Brain activation in response to a tactile stimulation: functional magnetic resonance imaging (FMRI) versus cognitive analysis.

  B Querleux, G Gazano, O Mohen-Domenech, J Jacquin, Y Burnod, P Gaudion, O Jolivet, J Bittoun, H Benali
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  ABSTRACT: Objective. The aim of this study was to compare fMRI analysis of somatosensory areas activated by passive touch, to cognitive analysis of the psychological profile of human subjects. Methods. The study was carried out on 21 females, after informed consent. Two artificial textures (smooth and rough), and two natural textures (the skin of an operator modified or not by a cosmetic product), were applied on the fingers of the subjects. A period of imagination to be touched was also included in the study. MR images of the somatosensory cortex were acquired on a 1.5T MRI system during the different behavioral conditions. Series of images were first processed to compensate for the inter-frame motions and then activation was assessed with a statistical method based on conditional analysis. After the MRI protocol, each subject was interviewed following a questionnaire from which psychological descriptors were extracted. Results. 1) Activations were quite similar for all textures in the contralateral sensory areas 2) In the ipsilateral sensory areas, activations were more important in response to a stimulation with the skin of an operator than with artificial textures. The activation was even more important after application of a cosmetic product on the skin. 3) Imagination of the tactile stimulation resulted in an activation mostly localized in the ipsilateral cortex. 4) A PLS analysis assessed that 2 psychological descriptors, rationality and sensorial reactivity, were related to an activation in the contralateral cortex, while 2 others, imagination and sensitivity, were related to ipsilateral areas activation. Conclusion. fMRI and cognitive analysis allowed us to map the physical component of the tactile perception in the contralateral cortex. This study also gave rise to a better understanding of the activation in ipsilateral areas, which was found to be mainly related to the subjective component of the stimulation.
  International Journal of Cosmetic Science 05/1999; 21(2):107-18.
• Article: Bayesian inference in populations of cortical neurons: a model of motion integration and segmentation in area MT.

  E Koechlin, J L Anton, Y Burnod
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  ABSTRACT: A major issue in cortical physiology and computational neuroscience is understanding the interaction between extrinsic signals from feedforward connections and intracortical signals from lateral connections. We propose here a computational model for motion perception based on the assumption that the local cortical circuits in the medio-temporal area (area MT) implement a Bayesian inference principle. This approach establishes a functional balance between feedforward and lateral, excitatory and inhibitory, inputs. The model reproduces most of the known properties of the neurons in area MT in response to moving stimuli. It accounts for important motion perception phenomena including motion transparency, spatial and temporal integration/segmentation. While integrating several properties of previously proposed models, it makes specific testable predictions concerning, in particular, temporal properties of neurons and the architecture of lateral connections in area MT. In addition, the proposed mechanism is consistent with the known properties of local cortical circuits in area V1. This suggests that Bayesian inference may be a general feature of information processing in cortical neuron populations.
  Biological Cybernetics 02/1999; 80(1):25-44. · 1.59 Impact Factor
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  Available from: Jean-Claude Dreher

  Article: Planning dysfunction in schizophrenia: impairment of potentials preceding fixed/free and single/sequence of self-initiated finger movements.

  J C Dreher, W Trapp, J P Banquet, M Keil, W Günther, Y Burnod
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  ABSTRACT: To test the hypothesis of a planning dysfunction in schizophrenia using a precise temporal definition, the readiness potential (RP), a negative cortical wave preceding self-initiated movements and reflecting motor preparation processes, was studied in patients under stable medication and in controls. The supplementary motor area (SMA), known to be involved in the generation of the RP, has also been implicated in movement selection (fixed versus free) and complexity (single versus sequence). This is the first study using RP for the assessment of the influence of these factors on motor preparation in schizophrenics. Our results show that schizophrenics' RP amplitude is significantly lower than in controls at central and contralateral electrodes. However, RP amplitude increases with task difficulty in both groups, offering important new insight into classical SMA hypoactivation in schizophrenics performing motor tasks. Topographic analysis shows that RP amplitude is, for both groups, significantly higher in sequence than in single movements at fronto-central sites and higher for free than for fixed movements at centro-parietal sites. Finally, RP onset occurs significantly later in schizophrenics than in controls. These results support the view of a motor-preparation and decision-making dysfunction in schizophrenia. They are interpreted within the framework of a fronto-striatal disorder in this disease.
  Experimental Brain Research 02/1999; 124(2):200-14. · 2.39 Impact Factor
• Article: Early motor influences on visuomotor transformations for reaching: a positive image of optic ataxia.

  A Battaglia Mayer, S Ferraina, B Marconi, J B Bullis, F Lacquaniti, Y Burnod, P Baraduc, R Caminiti
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  ABSTRACT: Coding of reaching in the cerebral cortex is based on the operation of distributed populations of parietal and frontal neurons, whose main functional characteristics reside in their combinatorial power, i.e., in the capacity for combining different information related to the spatial aspects of reaching. The tangential distribution of reach-related neurons endowed with different functional properties changes gradually in the cortex and defines, in the parieto-frontal network, trends of functional properties. These visual-to-somatic gradients imply the existence of cortical regions of functional overlaps, i.e., of combinatorial domains, where the integration of different reach-related signals occurs. Studies of early coding of reaching in the mesial parietal areas show how somatomotor information, such as that related to arm posture and movement, influences neuronal activity in the very early stages of the visuomotor transformation underlying the composition of the motor command and is not added "downstream" in the frontal cortex. This influence is probably due to re-entrant signals traveling through fronto-parietal-association connections. Together with the gradient architecture of the network and the reciprocity of cortico-cortical connections, this implies that coding of reaching cannot be regarded as a top-down, serial sequence of coordinate transformation, each performed by a given cortical area, but as a recursive process, where different signals are progressively matched and further elaborated locally, due to intrinsic cortical connections. This model of reaching is also supported by psychophysical studies stressing the parallel processing of the different relevant parameters and the "hybrid" nature of the reference frame where they are combined. The theoretical frame presented here can also offer a background for a new interpretation of a well-known visuomotor disorder, due to superior parietal lesions, i.e., optic ataxia. More than a disconnection syndrome, this can now be interpreted as the consequence of the breakdown of the operations occurring in the combinatorial domains of the superior parietal segment of the parieto-frontal network.
  Experimental Brain Research 12/1998; 123(1-2):172-89. · 2.39 Impact Factor
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  Available from: free.fr

  Article: Bistable behaviour in a neocortical neurone model.

  B Delord, A J Klaassen, Y Burnod, R Costalat, E Guigon
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  ABSTRACT: Intracellular recordings have shown that neocortical pyramidal neurones have an intrinsic capacity for regenerative firing. The cellular mechanism of this firing was investigated by computer simulations of a model neurone endowed with standard action potential and persistent sodium (gNaP) conductances. The firing mode of the neurone was determined as a function of leakage and NaP maximal conductances (gl and gNaP). The neurone had two stable states of activity (bistable) over wide range of gl and gNaP, one at the resting potential and the other in a regenerative firing mode, that could be triggered by a transient input. This model points to a cellular mechanism that may contribute to the generation and maintenance of long-lasting sustained neuronal discharges in the cerebral cortex.
  Neuroreport 04/1997; 8(4):1019-23. · 1.66 Impact Factor
• Article: Functional MR imaging of the human sensorimotor cortex during haptic discrimination.

  J L Anton, H Benali, E Guigon, M Di Paola, J Bittoun, O Jolivet, Y Burnod
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  ABSTRACT: This study attempted to determine whether haptic discriminations of shape (haptic task) activate the same tissue in the central cortical region of normal human subjects as do finger movements (opposition task). Opposition and haptic tasks both activated the central sulcus, as expected from previous imaging studies. The haptic task activated about 50% of the cortical territory activated by the opposition task. The results suggest that exploratory digital movements performed to collect precise somatosensory information and automatic movements performed during finger positioning activate partially overlapping parts of the sensorimotor cortex.
  Neuroreport 12/1996; 7(18):2849-52. · 1.66 Impact Factor
• Article: Dynamical computational properties of local cortical networks for visual and motor processing: a bayesian framework.

  E Koechlin, J L Anton, Y Burnod
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  ABSTRACT: A major unsolved question concerns the interaction between the coding of information in the cortex and the collective neural operations (such as perceptual grouping, mental rotation) that can be performed on this information. A key property of the local networks in the cerebral cortex is to combine thalamocortical or feedforward information with horizontal cortico-cortical connections. Among different types of neural networks compatible with the known functional and architectural properties of the cortex, we show that there exist interesting bayesian solutions resulting in an optimal collective decision made by the neuronal population. We suggest that thalamo-cortical and cortico-cortical synaptic plasticity can be differentially modulated to optimize this collective bayesian decision process. We take two examples of cortical dynamics, one for perceptual grouping in MT, and the other one for mental rotation in M1. We show that a neural implementation of the bayesian principle is both computationally efficient to perform these tasks and consistent with the experimental data on the related neuronal activities. A major implication is that a similar collective decision mechanism should exist in different cortical regions due to the similarity of the cortical functional architecture.
  Journal of Physiology-Paris 02/1996; 90(3-4):257-62. · 1.31 Impact Factor
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  Available from: free.fr

  Article: Modelling the acquisition of goal-directed behaviors by populations of neurons.

  E Guigon, Y Burnod
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  ABSTRACT: Recent neurophysiological studies have revealed the patterns of neuronal activity during the acquisition of goal-directed behaviors, both in single cells, and in large populations of neurons. We propose a model which helps three sets of experimental results in the monkey to be understood: (1) activity of single cells vary greatly and only population activities are causally related to behavior. The model shows how a population of stochastic neurons, whose behaviors vary widely, can learn a skilled conditioned movement with only local activity-dependent synaptic changes. (2) typical changes in neuronal activity occur when the rules governing the behavior are changed, i.e. when the relationship between cues and actions to reach a goal changes over time. There are two types of neuronal patterns during changes in reward contingency: a monotonic increasing pattern and a non-monotonic pattern which follows the change in the way the reward is obtained. Units in the model display these two types of change, which correspond to synaptic modifications related to the encoding of the behavioral significance of sensory and motor events. (3) These two patterns of neuronal activity define two populations whose anatomical distributions in the frontal lobe overlap with a gradient organized in the rostro-caudal direction. The model consists of two artificial neural networks, defined by the same set of equations, but which differ in the values of two parameters (P and Q). P defines the adaptive properties of processing units and Q describes the coding of information. The model suggests that a balance in the relative strengths of these parameters distributed along a rostro-caudal gradient can explain the distribution of neuronal types in the frontal lobe of the monkey.
  International Journal of Psychophysiology 04/1995; 19(2):103-13. · 2.14 Impact Factor