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Hannagan T, Agrawal A, Cohen L, Dehaene S. Emergence of a compositional neural code for written words: Recycling of a convolutional neural network for reading. Proc Natl Acad Sci U S A 2021; 118:e2104779118. [PMID: 34750255 PMCID: PMC8609650 DOI: 10.1073/pnas.2104779118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/10/2021] [Indexed: 11/18/2022] Open
Abstract
The visual word form area (VWFA) is a region of human inferotemporal cortex that emerges at a fixed location in the occipitotemporal cortex during reading acquisition and systematically responds to written words in literate individuals. According to the neuronal recycling hypothesis, this region arises through the repurposing, for letter recognition, of a subpart of the ventral visual pathway initially involved in face and object recognition. Furthermore, according to the biased connectivity hypothesis, its reproducible localization is due to preexisting connections from this subregion to areas involved in spoken-language processing. Here, we evaluate those hypotheses in an explicit computational model. We trained a deep convolutional neural network of the ventral visual pathway, first to categorize pictures and then to recognize written words invariantly for case, font, and size. We show that the model can account for many properties of the VWFA, particularly when a subset of units possesses a biased connectivity to word output units. The network develops a sparse, invariant representation of written words, based on a restricted set of reading-selective units. Their activation mimics several properties of the VWFA, and their lesioning causes a reading-specific deficit. The model predicts that, in literate brains, written words are encoded by a compositional neural code with neurons tuned either to individual letters and their ordinal position relative to word start or word ending or to pairs of letters (bigrams).
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Affiliation(s)
- T Hannagan
- Cognitive Neuroimaging Unit, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, INSERM, Université Paris-Saclay, NeuroSpin, Gif-Sur-Yvette 91191, France
- Collège de France, Université Paris Sciences Lettres 75005 Paris, France
| | - A Agrawal
- Cognitive Neuroimaging Unit, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, INSERM, Université Paris-Saclay, NeuroSpin, Gif-Sur-Yvette 91191, France
- Collège de France, Université Paris Sciences Lettres 75005 Paris, France
| | - L Cohen
- Sorbonne Université, INSERM U1127, CNRS UMR 7225, Institut du Cerveau et de la Moelle épinièr, Hôpital de la Pitié-Salpêtrière, Paris 75013, France
- Assistance Publique-Hôpitaux de Paris, Hôpital de la Pitié Salpêtrière, Fédération de Neurologie, Paris F-75013, France
| | - S Dehaene
- Cognitive Neuroimaging Unit, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, INSERM, Université Paris-Saclay, NeuroSpin, Gif-Sur-Yvette 91191, France;
- Collège de France, Université Paris Sciences Lettres 75005 Paris, France
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Demertzi A, Tagliazucchi E, Dehaene S, Deco G, Barttfeld P, Raimondo F, Martial C, Fernández-Espejo D, Rohaut B, Voss HU, Schiff ND, Owen AM, Laureys S, Naccache L, Sitt JD. Human consciousness is supported by dynamic complex patterns of brain signal coordination. Sci Adv 2019; 5:eaat7603. [PMID: 30775433 PMCID: PMC6365115 DOI: 10.1126/sciadv.aat7603] [Citation(s) in RCA: 201] [Impact Index Per Article: 40.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Accepted: 12/19/2018] [Indexed: 05/23/2023]
Abstract
Adopting the framework of brain dynamics as a cornerstone of human consciousness, we determined whether dynamic signal coordination provides specific and generalizable patterns pertaining to conscious and unconscious states after brain damage. A dynamic pattern of coordinated and anticoordinated functional magnetic resonance imaging signals characterized healthy individuals and minimally conscious patients. The brains of unresponsive patients showed primarily a pattern of low interareal phase coherence mainly mediated by structural connectivity, and had smaller chances to transition between patterns. The complex pattern was further corroborated in patients with covert cognition, who could perform neuroimaging mental imagery tasks, validating this pattern's implication in consciousness. Anesthesia increased the probability of the less complex pattern to equal levels, validating its implication in unconsciousness. Our results establish that consciousness rests on the brain's ability to sustain rich brain dynamics and pave the way for determining specific and generalizable fingerprints of conscious and unconscious states.
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Affiliation(s)
- A. Demertzi
- GIGA-Consciousness, GIGA Institute B34, University of Liège, Avenue de l’Hôpital, 11, 4000 Sart Tilman, Belgium
- INSERM, U 1127, F-75013 Paris, France
- Institut du Cerveau et de la Moelle Epinière, Hôpital Pitié-Salpêtrière, 47 bd de l’Hôpital, 75013 Paris, France
| | - E. Tagliazucchi
- Institut du Cerveau et de la Moelle Epinière, Hôpital Pitié-Salpêtrière, 47 bd de l’Hôpital, 75013 Paris, France
- Instituto de Física de Buenos Aires and Physics Deparment (University of Buenos Aires), Buenos Aires, Argentina
| | - S. Dehaene
- Cognitive Neuroimaging Unit, CEA, INSERM, Université Paris-Sud, Université Paris-Saclay, F-91191 Gif/Yvette, France
- Collège de France, 11, Place Marcelin Berthelot, 75005 Paris, France
| | - G. Deco
- Center for Brain and Cognition, Computational Neuroscience Group, Department of Information and Communication Technologies, Universitat Pompeu Fabra, Calle Ramon Trias Fargas 25-27, Barcelona 08005, Spain
- Institucio Catalana de la Recerca I Estudis Avancats (ICREA), University of Pompeu Fabra, Passeig Lluis Companys 23, Barcelona 08010, Spain
| | - P. Barttfeld
- Laboratory of Integrative Neuroscience, Physics Department, FCEyN UBA and IFIBA, CONICET, Pabellón 1, Ciudad Universitaria, 1428 Buenos Aires, Argentina
| | - F. Raimondo
- GIGA-Consciousness, GIGA Institute B34, University of Liège, Avenue de l’Hôpital, 11, 4000 Sart Tilman, Belgium
- INSERM, U 1127, F-75013 Paris, France
- Institut du Cerveau et de la Moelle Epinière, Hôpital Pitié-Salpêtrière, 47 bd de l’Hôpital, 75013 Paris, France
- Department of Computer Science, Faculty of Exact and Natural Sciences, Intendente Güiraldes 2160–Ciudad Universitaria–C1428EGA, University of Buenos Aires, Argentina
- Sorbonne Universités, UPMC Université Paris 06, Faculté de Médecine Pitié-Salpêtrière, 91-105 bd de l’Hôpital, 75013 Paris, France
- CONICET–Universidad de Buenos Aires, Instituto de Investigación en Ciencias de la Computación, Godoy Cruz 2290, C1425FQB Ciudad Autónoma de Buenos Aires, Argentina
| | - C. Martial
- GIGA-Consciousness, GIGA Institute B34, University of Liège, Avenue de l’Hôpital, 11, 4000 Sart Tilman, Belgium
| | - D. Fernández-Espejo
- Centre for Human Brain Health, University of Birmingham, B15 2TT Birmingham, UK
- School of Psychology, University of Birmingham, B15 2TT, Birmingham, UK
- The Brain and Mind Institute, Western Interdisciplinary Research Building, N6A 5B7 University of Western Ontario, London, Ontario, Canada
| | - B. Rohaut
- INSERM, U 1127, F-75013 Paris, France
- Institut du Cerveau et de la Moelle Epinière, Hôpital Pitié-Salpêtrière, 47 bd de l’Hôpital, 75013 Paris, France
- Department of Neurology, Columbia University, 710 West 168th Street, New York, NY 10032-3784, USA
| | - H. U. Voss
- Radiology Department, Citigroup Biomedical Imaging Center, Weill Cornell Medical College, 516 E. 72nd Street, New York, NY 10021, USA
| | - N. D. Schiff
- Feil Family Brain and Mind Research Institute, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA
| | - A. M. Owen
- The Brain and Mind Institute, Western Interdisciplinary Research Building, N6A 5B7 University of Western Ontario, London, Ontario, Canada
| | - S. Laureys
- GIGA-Consciousness, GIGA Institute B34, University of Liège, Avenue de l’Hôpital, 11, 4000 Sart Tilman, Belgium
| | - L. Naccache
- INSERM, U 1127, F-75013 Paris, France
- Institut du Cerveau et de la Moelle Epinière, Hôpital Pitié-Salpêtrière, 47 bd de l’Hôpital, 75013 Paris, France
| | - J. D. Sitt
- INSERM, U 1127, F-75013 Paris, France
- Institut du Cerveau et de la Moelle Epinière, Hôpital Pitié-Salpêtrière, 47 bd de l’Hôpital, 75013 Paris, France
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3
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Hannagan T, Nieder A, Viswanathan P, Dehaene S. A random-matrix theory of the number sense. Philos Trans R Soc Lond B Biol Sci 2018; 373:rstb.2017.0253. [PMID: 29292354 DOI: 10.1098/rstb.2017.0253] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/23/2017] [Indexed: 01/29/2023] Open
Abstract
Number sense, a spontaneous ability to process approximate numbers, has been documented in human adults, infants and newborns, and many other animals. Species as distant as monkeys and crows exhibit very similar neurons tuned to specific numerosities. How number sense can emerge in the absence of learning or fine tuning is currently unknown. We introduce a random-matrix theory of self-organized neural states where numbers are coded by vectors of activation across multiple units, and where the vector codes for successive integers are obtained through multiplication by a fixed but random matrix. This cortical implementation of the 'von Mises' algorithm explains many otherwise disconnected observations ranging from neural tuning curves in monkeys to looking times in neonates and cortical numerotopy in adults. The theory clarifies the origin of Weber-Fechner's Law and yields a novel and empirically validated prediction of multi-peak number neurons. Random matrices constitute a novel mechanism for the emergence of brain states coding for quantity.This article is part of a discussion meeting issue 'The origins of numerical abilities'.
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Affiliation(s)
- T Hannagan
- Cognitive Neuroimaging Unit, CEA DSV/I2BM, INSERM, Université Paris-Sud, Université Paris-Saclay, NeuroSpin center, 91191 Gif/Yvette, France
| | - A Nieder
- Animal Physiology, Institute of Neurobiology, University of Tübingen, 72076 Tübingen, Germany
| | - P Viswanathan
- Animal Physiology, Institute of Neurobiology, University of Tübingen, 72076 Tübingen, Germany
| | - S Dehaene
- Cognitive Neuroimaging Unit, CEA DSV/I2BM, INSERM, Université Paris-Sud, Université Paris-Saclay, NeuroSpin center, 91191 Gif/Yvette, France.,Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France
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Barttfeld P, Abboud S, Lagercrantz H, Adén U, Padilla N, Edwards AD, Cohen L, Sigman M, Dehaene S, Dehaene-Lambertz G. A lateral-to-mesial organization of human ventral visual cortex at birth. Brain Struct Funct 2018; 223:3107-3119. [PMID: 29752588 DOI: 10.1007/s00429-018-1676-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2017] [Accepted: 05/03/2018] [Indexed: 12/20/2022]
Abstract
In human adults, ventral extra-striate visual cortex contains a mosaic of functionally specialized areas, some responding preferentially to natural visual categories such as faces (fusiform face area) or places (parahippocampal place area) and others to cultural inventions such as written words and numbers (visual word form and number form areas). It has been hypothesized that this mosaic arises from innate biases in cortico-cortical connectivity. We tested this hypothesis by examining functional resting-state correlation at birth using fMRI data from full-term human newborns. The results revealed that ventral visual regions are functionally connected with their contra-lateral homologous regions and also exhibit distinct patterns of long-distance functional correlation with anterior associative regions. A mesial-to-lateral organization was observed, with the signal of the more lateral regions, including the sites of visual word and number form areas, exhibiting higher correlations with voxels of the prefrontal, inferior parietal and temporal cortices, including language areas. Finally, we observed hemispheric asymmetries in the functional correlation of key areas of the language network that may influence later adult hemispheric lateralization. We suggest that long-distance circuits present at birth constrain the subsequent functional differentiation of the ventral visual cortex.
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Affiliation(s)
- P Barttfeld
- Cognitive Neuroimaging Unit, CEA DSV/I2BM, INSERM, Université Paris-Sud, Université Paris-Saclay, NeuroSpin Center, Gif-sur-Yvette, France. .,Instituto de Investigaciones Psicológicas (IIPsi), CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina.
| | - S Abboud
- INSERM, U 1127, Paris, 75013, France.,Institut Du Cerveau Et De La Moelle Epinière, ICM, PICNIC Lab, Paris, 75013, France
| | - H Lagercrantz
- Department of Women's and Children's Health, Karolinska Institutet, 171 76, Stockholm, Sweden
| | - U Adén
- Department of Women's and Children's Health, Karolinska Institutet, 171 76, Stockholm, Sweden
| | - N Padilla
- Department of Women's and Children's Health, Karolinska Institutet, 171 76, Stockholm, Sweden
| | - A D Edwards
- Centre for the Developing Brain, Division of Imaging Sciences and Biomedical Engineering, King's College London, London, UK
| | - L Cohen
- INSERM, U 1127, Paris, 75013, France.,Institut Du Cerveau Et De La Moelle Epinière, ICM, PICNIC Lab, Paris, 75013, France
| | - M Sigman
- Universidad Torcuato Di Tella, Almirante Juan Saenz Valiente 1010, C1428BIJ, Buenos Aires, Argentina
| | - S Dehaene
- Cognitive Neuroimaging Unit, CEA DSV/I2BM, INSERM, Université Paris-Sud, Université Paris-Saclay, NeuroSpin Center, Gif-sur-Yvette, France.,Collège de France, 75005, Paris, France
| | - G Dehaene-Lambertz
- Cognitive Neuroimaging Unit, CEA DSV/I2BM, INSERM, Université Paris-Sud, Université Paris-Saclay, NeuroSpin Center, Gif-sur-Yvette, France
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Berkovitch L, Del Cul A, Maheu M, Dehaene S. Impaired conscious access and abnormal attentional amplification in schizophrenia. Neuroimage Clin 2018; 18:835-848. [PMID: 29876269 PMCID: PMC5988039 DOI: 10.1016/j.nicl.2018.03.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/09/2017] [Revised: 03/09/2018] [Accepted: 03/13/2018] [Indexed: 11/25/2022]
Abstract
Previous research suggests that the conscious perception of a masked stimulus is impaired in schizophrenia, while unconscious bottom-up processing of the same stimulus, as assessed by subliminal priming, can be preserved. Here, we test this postulated dissociation between intact bottom-up and impaired top-down processing and evaluate its brain mechanisms using high-density recordings of event-related potentials. Sixteen patients with schizophrenia and sixteen controls were exposed to peripheral digits with various degrees of visibility, under conditions of either focused attention or distraction by another task. In the distraction condition, the brain activity evoked by masked digits was drastically reduced in both groups, but early bottom-up visual activation could still be detected and did not differ between patients and controls. By contrast, under focused top-down attention, a major impairment was observed: in patients, contrary to controls, the late non-linear ignition associated with the P3 component was reduced. Interestingly, the patients showed an essentially normal attentional amplification of the P1 and N2 components. These results suggest that some but not all top-down attentional amplification processes are impaired in schizophrenia, while bottom-up processing seems to be preserved. An elevated consciousness threshold is observed in schizophrenia. Under unattended conditions, brain activity was similarly reduced in schizophrenic patients and controls. Under attended conditions, the late ignition associated with the P3 component is impaired in patients. In schizophrenia, top-down attentional amplification is abnormal while bottom-up processing is essentially spared.
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Affiliation(s)
- L Berkovitch
- Cognitive Neuroimaging Unit, CEA DSV/I2BM, INSERM, Université Paris-Sud, Université Paris-Saclay, NeuroSpin Center, 91191 Gif-sur-Yvette, France; Sorbonne Universités, UPMC Univ Paris 06, IFD, 4 place Jussieu, 75252 Paris Cedex 05, France.
| | - A Del Cul
- AP-HP, Groupe Hospitalier Pitié-Salpêtrière, Service de Psychiatrie d'Adultes, 75013 Paris, France; Inserm, CNRS, APHP, Institut du Cerveau et de la Moelle (ICM), Hôpital Pitié-Salpêtrière, Sorbonne Universités, UPMC Univ Paris 06, 75013 Paris, France
| | - M Maheu
- Cognitive Neuroimaging Unit, CEA DSV/I2BM, INSERM, Université Paris-Sud, Université Paris-Saclay, NeuroSpin Center, 91191 Gif-sur-Yvette, France; Université Paris Descartes, Sorbonne Paris Cité, 75006 Paris, France
| | - S Dehaene
- Cognitive Neuroimaging Unit, CEA DSV/I2BM, INSERM, Université Paris-Sud, Université Paris-Saclay, NeuroSpin Center, 91191 Gif-sur-Yvette, France; Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France
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6
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Sun ZY, Pinel P, Rivière D, Moreno A, Dehaene S, Mangin JF. Linking morphological and functional variability in hand movement and silent reading. Brain Struct Funct 2015; 221:3361-71. [DOI: 10.1007/s00429-015-1106-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Accepted: 08/27/2015] [Indexed: 10/23/2022]
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Amunts K, Hawrylycz MJ, Van Essen DC, Van Horn JD, Harel N, Poline JB, De Martino F, Bjaalie JG, Dehaene-Lambertz G, Dehaene S, Valdes-Sosa P, Thirion B, Zilles K, Hill SL, Abrams MB, Tass PA, Vanduffel W, Evans AC, Eickhoff SB. Interoperable atlases of the human brain. Neuroimage 2014; 99:525-32. [PMID: 24936682 DOI: 10.1016/j.neuroimage.2014.06.010] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Revised: 05/05/2014] [Accepted: 06/02/2014] [Indexed: 12/11/2022] Open
Abstract
The last two decades have seen an unprecedented development of human brain mapping approaches at various spatial and temporal scales. Together, these have provided a large fundus of information on many different aspects of the human brain including micro- and macrostructural segregation, regional specialization of function, connectivity, and temporal dynamics. Atlases are central in order to integrate such diverse information in a topographically meaningful way. It is noteworthy, that the brain mapping field has been developed along several major lines such as structure vs. function, postmortem vs. in vivo, individual features of the brain vs. population-based aspects, or slow vs. fast dynamics. In order to understand human brain organization, however, it seems inevitable that these different lines are integrated and combined into a multimodal human brain model. To this aim, we held a workshop to determine the constraints of a multi-modal human brain model that are needed to enable (i) an integration of different spatial and temporal scales and data modalities into a common reference system, and (ii) efficient data exchange and analysis. As detailed in this report, to arrive at fully interoperable atlases of the human brain will still require much work at the frontiers of data acquisition, analysis, and representation. Among them, the latter may provide the most challenging task, in particular when it comes to representing features of vastly different scales of space, time and abstraction. The potential benefits of such endeavor, however, clearly outweigh the problems, as only such kind of multi-modal human brain atlas may provide a starting point from which the complex relationships between structure, function, and connectivity may be explored.
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Affiliation(s)
- K Amunts
- Institute of Neuroscience and Medicine, INM-1, Research Centre Jülich, Germany; C. and O. Vogt Institute for Brain Research, Heinrich Heine University, Düsseldorf, Germany
| | | | - D C Van Essen
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO, USA
| | - J D Van Horn
- The Institute for Neuroimaging and Informatics (INI) and Laboratory for Neuro Imaging (LONI), Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - N Harel
- Center for Magnetic Resonance Research, Departments of Radiology & Neurosurgery, University of Minnesota School of Medicine, Minneapolis, MN, USA
| | - J-B Poline
- Hellen Wills Neuroscience Institute, Brain Imaging Center, University of California at Berkeley, CA, USA
| | - F De Martino
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - J G Bjaalie
- Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | | | - S Dehaene
- INSERM, U992, Cognitive Neuroimaging Unit, F-91191 Gif/Yvette, France
| | - P Valdes-Sosa
- Cuban Neuroscience Center, Havana, Cuba; Key Laboratory for Neuroinformation, Chengudu, China
| | - B Thirion
- Parietal Research Team, French Institute for Research in Computer Science and Automation (INRIA), Gif sur Yvette, France
| | - K Zilles
- Department of Psychiatry, Psychotherapy and Psychosomatics, RWTH University Aachen, Aachen, Germany; Jülich-Aachen Research Alliance (JARA), Translational Brain Medicine, Jülich, Germany
| | - S L Hill
- International Neuroinformatics Coordinating Facility Secretariat (INCF), Stockholm, Sweden
| | - M B Abrams
- International Neuroinformatics Coordinating Facility Secretariat (INCF), Stockholm, Sweden.
| | - P A Tass
- Institute of Neuroscience and Medicine, INM-1, Research Centre Jülich, Germany; Department of Neuromodulation, University of Cologne, Cologne, Germany; Department of Neurosurgery, Stanford University, Stanford, USA
| | - W Vanduffel
- Department of Neurosciences, KU Leuven, Leuven, Belgium
| | - A C Evans
- Montreal Neurological Institute, McGill University, Montreal, Canada
| | - S B Eickhoff
- Institute of Neuroscience and Medicine, INM-1, Research Centre Jülich, Germany; Institute for Clinical Neuroscience and Medical Psychology, Heinrich-Heine University, Düsseldorf, Germany
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King JR, Dehaene S. A model of subjective report and objective discrimination as categorical decisions in a vast representational space. Philos Trans R Soc Lond B Biol Sci 2014; 369:20130204. [PMID: 24639577 PMCID: PMC3965160 DOI: 10.1098/rstb.2013.0204] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Subliminal perception studies have shown that one can objectively discriminate a stimulus without subjectively perceiving it. We show how a minimalist framework based on Signal Detection Theory and Bayesian inference can account for this dissociation, by describing subjective and objective tasks with similar decision-theoretic mechanisms. Each of these tasks relies on distinct response classes, and therefore distinct priors and decision boundaries. As a result, they may reach different conclusions. By formalizing, within the same framework, forced-choice discrimination responses, subjective visibility reports and confidence ratings, we show that this decision model suffices to account for several classical characteristics of conscious and unconscious perception. Furthermore, the model provides a set of original predictions on the nonlinear profiles of discrimination performance obtained at various levels of visibility. We successfully test one such prediction in a novel experiment: when varying continuously the degree of perceptual ambiguity between two visual symbols presented at perceptual threshold, identification performance varies quasi-linearly when the stimulus is unseen and in an 'all-or-none' manner when it is seen. The present model highlights how conscious and non-conscious decisions may correspond to distinct categorizations of the same stimulus encoded by a high-dimensional neuronal population vector.
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Affiliation(s)
- J-R. King
- Cognitive Neuroimaging Unit, Institut National de la Santé et de la Recherche Médicale, U992, Gif/Yvette 91191, France
- NeuroSpin Center, Institute of BioImaging Commissariat à l'Energie Atomique, Gif/Yvette 91191, France
- Institut du Cerveau et de la Moelle Épinière Research Center, Institut National de la Santé et de la Recherche Médicale, Paris U975, France
| | - S. Dehaene
- Cognitive Neuroimaging Unit, Institut National de la Santé et de la Recherche Médicale, U992, Gif/Yvette 91191, France
- NeuroSpin Center, Institute of BioImaging Commissariat à l'Energie Atomique, Gif/Yvette 91191, France
- Department of Life Sciences, Université Paris 11, Orsay, France
- Collège de France, Paris 75005, France
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Abstract
How does general anesthesia (GA) work? Anesthetics are pharmacological agents that target specific central nervous system receptors. Once they bind to their brain receptors, anesthetics modulate remote brain areas and end up interfering with global neuronal networks, leading to a controlled and reversible loss of consciousness. This remarkable manipulation of consciousness allows millions of people every year to undergo surgery safely most of the time. However, despite all the progress that has been made, we still lack a clear and comprehensive insight into the specific neurophysiological mechanisms of GA, from the molecular level to the global brain propagation. During the last decade, the exponential progress in neuroscience and neuro-imaging led to a significant step in the understanding of the neural correlates of consciousness, with direct consequences for clinical anesthesia. Far from shutting down all brain activity, anesthetics lead to a shift in the brain state to a distinct, highly specific and complex state, which is being increasingly characterized by modern neuro-imaging techniques. There are several clinical consequences and challenges that are arising from the current efforts to dissect GA mechanisms: the improvement of anesthetic depth monitoring, the characterization and avoidance of intra-operative awareness and post-anesthesia cognitive disorders, and the development of future generations of anesthetics.
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Affiliation(s)
- L Uhrig
- CEA, NeuroSpin center, 91191 Gif-sur-Yvette, France; Avenir-Bettencourt-Schueller, Inserm, 91191 Gif-sur-Yvette, France; Cognitive neuroimaging unit, Inserm, U992, 91191 Gif-sur-Yvette, France.
| | - S Dehaene
- CEA, NeuroSpin center, 91191 Gif-sur-Yvette, France; Cognitive neuroimaging unit, Inserm, U992, 91191 Gif-sur-Yvette, France; Collège de France, 75231 Paris, France; Université Paris-Sud, 91405 Orsay, France
| | - B Jarraya
- CEA, NeuroSpin center, 91191 Gif-sur-Yvette, France; Avenir-Bettencourt-Schueller, Inserm, 91191 Gif-sur-Yvette, France; Neuromodulation unit, department of neurosurgery, Foch Hospital, 92150 Suresnes, France; Université Versailles Saint-Quentin-en-Yvelines, 78000 Versailles, France
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10
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Eger E, Pinel P, Dehaene S, Kleinschmidt A. Spatially Invariant Coding of Numerical Information in Functionally Defined Subregions of Human Parietal Cortex. Cereb Cortex 2013; 25:1319-29. [DOI: 10.1093/cercor/bht323] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Mazoyer BM, Tzourio N, Frak V, Syrota A, Murayama N, Levrier O, Salamon G, Dehaene S, Cohen L, Mehler J. The cortical representation of speech. J Cogn Neurosci 2013; 5:467-79. [PMID: 23964919 DOI: 10.1162/jocn.1993.5.4.467] [Citation(s) in RCA: 413] [Impact Index Per Article: 37.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Abstract In this study, we compare regional cerebral blood flow (rCBF) while French monolingual subjects listen to continuous speech in an unknown language, to lists of French words, or to meaningful and distorted stories in French. Our results show that, in addition to regions devoted to single-word comprehension, processing of meaningful stories activates the left middle temporal gyrus, the left and right temporal poles, and a superior prefrontal area in the left frontal lobe. Among these regions, only the temporal poles remain activated whenever sentences with acceptable syntax and prosody are presented.
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van Gaal S, Naccache L, Meuwese J, Cohen L, Dehaene S. Logical semantic operations in the absence of visual awareness. J Vis 2013. [DOI: 10.1167/13.9.1143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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13
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King JR, Faugeras F, Gramfort A, Schurger A, El Karoui I, Sitt JD, Rohaut B, Wacongne C, Labyt E, Bekinschtein T, Cohen L, Naccache L, Dehaene S. Single-trial decoding of auditory novelty responses facilitates the detection of residual consciousness. Neuroimage 2013; 83:726-38. [PMID: 23859924 DOI: 10.1016/j.neuroimage.2013.07.013] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Revised: 07/01/2013] [Accepted: 07/04/2013] [Indexed: 11/27/2022] Open
Abstract
Detecting residual consciousness in unresponsive patients is a major clinical concern and a challenge for theoretical neuroscience. To tackle this issue, we recently designed a paradigm that dissociates two electro-encephalographic (EEG) responses to auditory novelty. Whereas a local change in pitch automatically elicits a mismatch negativity (MMN), a change in global sound sequence leads to a late P300b response. The latter component is thought to be present only when subjects consciously perceive the global novelty. Unfortunately, it can be difficult to detect because individual variability is high, especially in clinical recordings. Here, we show that multivariate pattern classifiers can extract subject-specific EEG patterns and predict single-trial local or global novelty responses. We first validate our method with 38 high-density EEG, MEG and intracranial EEG recordings. We empirically demonstrate that our approach circumvents the issues associated with multiple comparisons and individual variability while improving the statistics. Moreover, we confirm in control subjects that local responses are robust to distraction whereas global responses depend on attention. We then investigate 104 vegetative state (VS), minimally conscious state (MCS) and conscious state (CS) patients recorded with high-density EEG. For the local response, the proportion of significant decoding scores (M=60%) does not vary with the state of consciousness. By contrast, for the global response, only 14% of the VS patients' EEG recordings presented a significant effect, compared to 31% in MCS patients' and 52% in CS patients'. In conclusion, single-trial multivariate decoding of novelty responses provides valuable information in non-communicating patients and paves the way towards real-time monitoring of the state of consciousness.
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Affiliation(s)
- J R King
- Cognitive Neuroimaging Unit, Institut National de la Santé et de la Recherche Médicale, U992, F-91191 Gif/Yvette, France; NeuroSpin Center, Institute of BioImaging Commissariat à l'Energie Atomique, F-91191 Gif/Yvette, France; Institut du Cerveau et de la Moelle Épinière Research Center, Institut National de la Santé et de la Recherche Médicale, U975 Paris, France.
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14
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Kouider S, Stahlhut C, Gelskov SV, Barbosa LS, Dutat M, de Gardelle V, Christophe A, Dehaene S, Dehaene-Lambertz G. A Neural Marker of Perceptual Consciousness in Infants. Science 2013; 340:376-80. [DOI: 10.1126/science.1232509] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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15
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Thiebaut de Schotten M, Cohen L, Amemiya E, Braga LW, Dehaene S. Learning to Read Improves the Structure of the Arcuate Fasciculus. Cereb Cortex 2012; 24:989-95. [DOI: 10.1093/cercor/bhs383] [Citation(s) in RCA: 152] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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16
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Piazza M, Pinel P, Dehaene S. Objective correlates of an unusual subjective experience: A single-case study of number-form synaesthesia. Cogn Neuropsychol 2012; 23:1162-73. [PMID: 21049372 DOI: 10.1080/02643290600780080] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
There is a universal and often unconscious tendency to mentally associate the number sequence with a spatial continuum (the mental number line). Here we study one individual who reports a strong and vivid sense of space when processing numbers. For him, the number sequence has a precise spatial form: a curvilinear right-to-left oriented line. We used various tasks to demonstrate that this numerical-spatial association is not a mere figment of his imagination, but a constrained experiential phenomenon consistent across sessions and automatically triggered by the visual presentation of numbers. We also show that this idiosyncratic representation can coexist with another implicit association, the SNARC effect (Spatial-Numerical Association of Response Codes, where small numbers are associated with the left side of space). This effect is present in individuals without explicit number forms and is not affected in the present subject in spite of his reversed subjective representation.
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Affiliation(s)
- M Piazza
- INSERM, CEA, Cognitive Neuroimaging Unit, Orsay, France
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17
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Faugeras F, Rohaut B, Weiss N, Bekinschtein TA, Galanaud D, Puybasset L, Bolgert F, Sergent C, Cohen L, Dehaene S, Naccache L. Probing consciousness with event-related potentials in the vegetative state. Neurology 2011; 77:264-8. [PMID: 21593438 DOI: 10.1212/wnl.0b013e3182217ee8] [Citation(s) in RCA: 130] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE Probing consciousness in noncommunicating patients is a major medical and neuroscientific challenge. While standardized and expert behavioral assessment of patients constitutes a mandatory step, this clinical evaluation stage is often difficult and doubtful, and calls for complementary measures which may overcome its inherent limitations. Several functional brain imaging methods are currently being developed within this perspective, including fMRI and cognitive event-related potentials (ERPs). We recently designed an original rule extraction ERP test that is positive only in subjects who are conscious of the long-term regularity of auditory stimuli. METHODS In the present work, we report the results of this test in a population of 22 patients who met clinical criteria for vegetative state. RESULTS We identified 2 patients showing this neural signature of consciousness. Interestingly, these 2 patients showed unequivocal clinical signs of consciousness within the 3 to 4 days following ERP recording. CONCLUSIONS Taken together, these results strengthen the relevance of bedside neurophysiological tools to improve diagnosis of consciousness in noncommunicating patients.
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Affiliation(s)
- F Faugeras
- AP-HP, Groupe Hospitalier Pitié-Salpêtrière, Department of Neurophysiology, Paris, France
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18
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Vinckier F, Qiao E, Pallier C, Dehaene S, Cohen L. The impact of letter spacing on reading: a test of the bigram coding hypothesis. J Vis 2011; 11:1-21. [PMID: 21566152 DOI: 10.1167/11.6.8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Identifying letters and their relative positions is the basis of reading in literate adults. The Local Combinations Detector model hypothesizes that this ability results from the general organization of the visual system, whereby object encoding proceeds through a hierarchy of neural detectors that, in the case of reading, would be tuned to letters, bigrams, or other letter combinations. Given the increase of receptive fields by a factor of 2 to 3 from one neural level to the next, detectors should integrate information only for letters separated by at most 2 other characters. We test this prediction by measuring the impact of letter spacing on reading, purifying this effect from confounding variables. We establish that performance deteriorates non-linearly whenever letters are separated by at least 2 blank spaces, with the concomitant emergence of a word length effect. We then show that this cannot be reduced to an effect of physical size nor of visual eccentricity. Finally, we demonstrate that the threshold of about 2 spaces is constant across variations in font size. Those results support the hypothesis that the fast recognition of combinations of nearby letters plays a central role in the coding of words, such that interfering with this representation prevents the parallel analysis of letter strings.
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19
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Dehaene-Lambertz G, Montavont A, Jobert A, Allirol L, Dubois J, Hertz-Pannier L, Dehaene S. Language or music, mother or Mozart? Structural and environmental influences on infants' language networks. Brain Lang 2010; 114:53-65. [PMID: 19864015 DOI: 10.1016/j.bandl.2009.09.003] [Citation(s) in RCA: 150] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2009] [Revised: 07/15/2009] [Accepted: 09/06/2009] [Indexed: 05/21/2023]
Abstract
Understanding how language emerged in our species calls for a detailed investigation of the initial specialization of the human brain for speech processing. Our earlier research demonstrated that an adult-like left-lateralized network of perisylvian areas is already active when infants listen to sentences in their native language, but did not address the issue of the specialization of this network for speech processing. Here we used fMRI to study the organization of brain activity in two-month-old infants when listening to speech or to music. We also explored how infants react to their mother's voice relative to an unknown voice. The results indicate that the well-known structural asymmetry already present in the infants' posterior temporal areas has a functional counterpart: there is a left-hemisphere advantage for speech relative to music at the level of the planum temporale. The posterior temporal regions are thus differently sensitive to the auditory environment very early on, channelling speech inputs preferentially to the left side. Furthermore, when listening to the mother's voice, activation was modulated in several areas, including areas involved in emotional processing (amygdala, orbito-frontal cortex), but also, crucially, a large extent of the left posterior temporal lobe, suggesting that the mother's voice plays a special role in the early shaping of posterior language areas. Both results underscore the joint contributions of genetic constraints and environmental inputs in the fast emergence of an efficient cortical network for language processing in humans.
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20
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Grace AD, Izard V, Shutts K, Dehaene S, Spelke ES. Sensitivity to geometry in male and female children and adults in the U.S. and in an Amazonian indigene group. J Vis 2010. [DOI: 10.1167/6.6.19] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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21
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Pinel P, Dehaene-Lambertz G, Artiges E, LeBihan D, Dehaene S. Genetic and epigenetic influences on the functional inferotemporal correlates of the visual word and face processing. Neuroimage 2009. [DOI: 10.1016/s1053-8119(09)71125-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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22
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de Lange FP, Jensen O, Oostenveld R, Dehaene S. Tracking decision-related activity in the human brain using MEG. Neuroimage 2009. [DOI: 10.1016/s1053-8119(09)70680-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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23
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Reuter F, Liégeois-Chauvel C, Marquis P, Del Cul A, Malikova I, Confort-Gouny S, Zaaraoui W, Cozzone J, Pelletier J, Dehaene S, Ranjeva J, Audoin B. Electrophysiological correlates of access to consciousness in early multiple sclerosis patients. Neuroimage 2009. [DOI: 10.1016/s1053-8119(09)70032-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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24
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Affiliation(s)
- A Del Cul
- INSERM, Cognitive Neuroimaging Unit, Saclay, France.
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25
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Reuter F, Audoin B, Liégois-Chauvel C, Malikova I, Naccache L, Cohen L, Del Cul A, Cozzone P, Ali Chérif A, Dehaene S, Ranjeva JP, Pelletier J. Approche en IRMf de la perception visuelle consciente et non consciente au stade précoce de la sclérose en plaques. Rev Neurol (Paris) 2009. [DOI: 10.1016/s0035-3787(09)70022-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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26
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27
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Sigman M, Jobert A, Lebihan D, Dehaene S. Parsing a sequence of brain activations at psychological times using fMRI. Neuroimage 2007; 35:655-68. [PMID: 17275341 DOI: 10.1016/j.neuroimage.2006.05.064] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2005] [Revised: 05/14/2006] [Accepted: 05/23/2006] [Indexed: 10/23/2022] Open
Abstract
Identifying the sequence of computations which constitute a cognitive task is a fundamental problem in neuroscience. Here we show, using functional magnetic resonance imaging (fMRI), that we can parse, at the time scale of about 100 ms, the different stages of brain activations which compose a complex sequential task. To identify timing information from the slow blood oxygen level-dependent (BOLD) signal response, we use a simple analytic method, based on periodic stimulation and an analysis of covariation of the spectral parameters (phase and power spectrum at the stimulation frequency) with the different experimental conditions. We implement this strategy in a sequential task, where the onset and duration of different stages are under experimental control. We are able to detect changes in onset latency and in the duration of the response, in an invariant fashion across different brain regions, and reconstruct the stream of activations consistent with five distinct stages of processing of the task. Sensory and motor clusters activate in the expected order and for the expected duration. The timing of sensory activations is more precise than the timing of motor activation. We also parse in time the reading-verbal network: visual extrastriate and phonological access regions (supramarginal gyrus) activate at the time of word presentation, while the inferior frontal gyrus, the anterior cingulate and the supplementary motor area are activated during the rehearsal period.
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Affiliation(s)
- M Sigman
- Integrative Neuroscience Laboratory Physics Department, FCEyN, UBA, Buenos Aires,
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28
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Dehaene S, Jobert A, Naccache L, Ciuciu P, Poline JB, Le Bihan D, Cohen L. Letter Binding and Invariant Recognition of Masked Words. Behavioral and Neuroimaging Evidence. Psychol Sci 2004; 15:307-13. [PMID: 15102139 DOI: 10.1111/j.0956-7976.2004.00674.x] [Citation(s) in RCA: 246] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Fluent readers recognize visual words across changes in case and retinal location, while maintaining a high sensitivity to the arrangement of letters. To evaluate the automaticity and functional anatomy of invariant word recognition, we measured brain activity during subliminal masked priming. By preceding target words with an unrelated prime, a repeated prime, or an anagram made of the same letters, we separated letter-level and whole-word codes. By changing the case and the retinal location of primes and targets, we evaluated the invariance of those codes. Our results indicate that an invariant binding of letters into words is achieved unconsciously through a series of increasingly invariant stages in the left occipito-temporal pathway.
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Affiliation(s)
- S Dehaene
- Institut National de la Santé et de la Recherche Médicale, Unit 562, Service Hospitalier Frédéric Joliot, Orsay, France.
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29
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Molko N, Cachia A, Riviere D, Mangin JF, Bruandet M, LeBihan D, Cohen L, Dehaene S. Brain Anatomy in Turner Syndrome: Evidence for Impaired Social and Spatial-Numerical Networks. Cereb Cortex 2004; 14:840-50. [PMID: 15054057 DOI: 10.1093/cercor/bhh042] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Analysis of brain structure in Turner syndrome (TS) provides the opportunity to identify the consequences of the loss of one X chromosome on brain anatomy and to characterize the neural bases underlying the specific cognitive profile of TS subjects which includes deficits in spatial-numerical processing and social cognition. Fourteen subjects with TS and fourteen controls were investigated using voxel-based analysis of high resolution anatomical and diffusion tensor images and using sulcal morphometry. The analysis of anatomical images provided evidence for macroscopical changes in cortical regions involved in social cognition such as the left superior temporal sulcus and orbito-frontal cortex and in a region involved in spatial and numerical cognition such as the right intraparietal sulcus. Diffusion tensor images showed a displacement of the grey-white matter interface of the left and right superior temporal sulcus and revealed bilateral microstructural anomalies in the temporal white matter. The analysis of fiber orientation suggests specific alterations of fiber tracts connecting posterior to anterior temporal regions. Last, sulcal morphometry confirmed the anomalies of the left and right superior temporal sulci and of the right intraparietal sulcus. Our results thus provide converging evidence of regionally specific structural changes in TS that are highly consistent with the hallmark symptoms associated with TS.
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Affiliation(s)
- N Molko
- INSERM U 562, Service Hospitalier Frédéric Joliot, CEA/DSV, IFR 49, Orsay cedex, France.
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30
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Cohen L, Martinaud O, Lemer C, Lehéricy S, Samson Y, Obadia M, Slachevsky A, Dehaene S. Visual Word Recognition in the Left and Right Hemispheres: Anatomical and Functional Correlates of Peripheral Alexias. Cereb Cortex 2003; 13:1313-33. [PMID: 14615297 DOI: 10.1093/cercor/bhg079] [Citation(s) in RCA: 288] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
According to a simple anatomical and functional model of word reading, letters displayed in one hemifield are first analysed through a cascade of contralateral retinotopic areas, which compute increasingly abstract representations. Eventually, an invariant representation of letter identities is created in the visual word form area (VWFA), reproducibly located within the left occipito-temporal sulcus. The VWFA then projects to structures involved in phonological or lexico-semantic processing. This model yields detailed predictions on the reading impairments that may follow left occipitotemporal lesions. Those predictions were confronted to behavioural, anatomical and functional MRI data gathered in normals and in patients suffering from left posterior cerebral artery infarcts. In normal subjects, alphabetic stimuli activated both the VWFA and the right-hemispheric symmetrical region (R-VWFA) relative to fixation, but only the VWFA showed a preference for alphabetic strings over simple chequerboards. The comparison of normalized brain lesions with reading-induced activations showed that the critical lesion site for the classical syndrome of pure alexia can be tightly localized to the VWFA. Reading impairments resulting from deafferentation of an intact VWFA from right- or left-hemispheric input were dissected using the same methods, shedding light on the connectivity of the VWFA. Finally, the putative role of right-hemispheric processing in the letter-by-letter reading strategy was clarified. In a letter-by-letter reader, the R-VWFA assumed some of the functional properties normally specific to the VWFA. These data corroborate our initial model of normal word perception and underline that an alternative right-hemispheric pathway can underlie functional recovery from alexia.
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Affiliation(s)
- L Cohen
- Institut de Neurologie, Hôpital de la Salpêtrière, AP-HP, Paris, France.
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31
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Pallier C, Dehaene S, Poline JB, LeBihan D, Argenti AM, Dupoux E, Mehler J. Brain imaging of language plasticity in adopted adults: can a second language replace the first? Cereb Cortex 2003; 13:155-61. [PMID: 12507946 DOI: 10.1093/cercor/13.2.155] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Do the neural circuits that subserve language acquisition lose plasticity as they become tuned to the maternal language? We tested adult subjects born in Korea and adopted by French families in childhood; they have become fluent in their second language and report no conscious recollection of their native language. In behavioral tests assessing their memory for Korean, we found that they do not perform better than a control group of native French subjects who have never been exposed to Korean. We also used event-related functional magnetic resonance imaging to monitor cortical activations while the Korean adoptees and native French listened to sentences spoken in Korean, French and other, unknown, foreign languages. The adopted subjects did not show any specific activations to Korean stimuli relative to unknown languages. The areas activated more by French stimuli than by foreign stimuli were similar in the Korean adoptees and in the French native subjects, but with relatively larger extents of activation in the latter group. We discuss these data in light of the critical period hypothesis for language acquisition.
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Affiliation(s)
- C Pallier
- INSERM U562, Service Hospitalier Fredrik Joliot, CEA/DSV/DRM, & IFR49, 4 place du Général Leclerc, Orsay, France.
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32
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Pappata S, Dehaene S, Poline JB, Gregoire MC, Jobert A, Delforge J, Frouin V, Bottlaender M, Dolle F, Di Giamberardino L, Syrota A. In vivo detection of striatal dopamine release during reward: a PET study with [(11)C]raclopride and a single dynamic scan approach. Neuroimage 2002; 16:1015-27. [PMID: 12202089 DOI: 10.1006/nimg.2002.1121] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A new simple method is proposed to detect, using PET and [(11)C]raclopride, changes in striatal extracellular dopamine concentration during a rewarded effortful task. This approach aimed to increase the sensitivity in detection of these effects. It requires a single-dynamic PET study and combines the classic kinetic compartmental model with the general linear model of SPM to provide statistical inference on changes in [(11)C]raclopride time-activity curve due to endogenous dopamine release during two short periods of activation. Kinetic simulations predicted that 100% dopamine increase during two 5-min periods starting at 30 and 60 min after the injection can be detected. Moreover the effects of dopamine release on the [(11)C]raclopride time-activity-curve are different from those induced by CBF increase. These simulated curves were used to construct the statistical linear model and to test voxel-by-voxel in healthy subjects the hypothesis that dopamine is released in the ventral striatum during periods of unexpected monetary gains, but not during periods of unexpected monetary loss. The experimental results are in line with the expected results although the amplitude of the effects due to dopamine release is moderate. The advantages and the limits of this method as well as the relevance of the results for dopamine involvement in reward processing are discussed.
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Affiliation(s)
- S Pappata
- INSERM U334, Service Hospitalier Frédéric Joliot, 4 Place du Géneral Leclerc, 91401, Orsay, France.
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33
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Molko N, Cohen L, Mangin JF, Chochon F, Lehéricy S, Le Bihan D, Dehaene S. Visualizing the neural bases of a disconnection syndrome with diffusion tensor imaging. J Cogn Neurosci 2002; 14:629-36. [PMID: 12126503 DOI: 10.1162/08989290260045864] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Disconnection syndromes are often conceptualized exclusively within cognitive box-and-arrow diagrams unrelated to brain anatomy. In a patient with alexia in his left visual field resulting from a posterior callosal lesion, we illustrate how diffusion tensor imaging can reveal the anatomical bases of a disconnection syndrome by tracking the degeneration of neural pathways and relating it to impaired fMRI activations and behavior. Compared to controls, an abnormal pattern of brain activity was observed in the patient during word reading, with a lack of activation of the left visual word form area (VWFA) by left hemifield words. Statistical analyses of diffusion images revealed a damaged fiber tract linking the left ventral occipito-temporal region to its right homolog across the lesioned area of corpus callosum and stopping close to the areas found active in fMRI. The behavioral disconnection syndrome could, thus, be related functionally to abnormal fMRI activations and anatomically to the absence of a connection between those activations. The present approach, based on the "negative tracking" of degenerated bundles, provides new perspectives on the understanding of human brain connections and disconnections.
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Affiliation(s)
- N Molko
- INSERM, Service Hospitalier Frédéric Joliot, Orsay cedex, France
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34
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Abstract
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.
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Affiliation(s)
- P Pinel
- Unité INSERM 334, Service Hospitalier Frédéric Joliot, Orsay Cedex, 91401, France
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35
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Naccache L, Dehaene S. The priming method: imaging unconscious repetition priming reveals an abstract representation of number in the parietal lobes. Cereb Cortex 2001; 11:966-74. [PMID: 11549619 DOI: 10.1093/cercor/11.10.966] [Citation(s) in RCA: 335] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Most of the current brain imaging methods are limited by the low spatial resolution of neuroimaging techniques and remain unable to measure activity at the scale of single neurons or small columns of neurons, which are the coding elements of the nervous system. In this work we have adapted the priming method, an emerging research strategy that can overcome some of these spatial limitations, to investigate the coding of numerical quantities in the human brain. This approach combines the logic of psychological priming experiments with the recently discovered neurophysiological phenomenon called repetition suppression (RS). In each trial, while subjects perform a constant task, a subliminal prime is presented prior to each target. By varying the relationship between prime and target, one can detect which brain areas present RS specifically for any given level of prime-target repetition. We first expose the general logic, potential and limitations of the priming method and then illustrate it by demonstrating that a region of parietal cortex is coding for numbers at the quantity level, independently of other stimulus attributes, and that this region processes both consciously and unconsciously perceived stimuli.
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Affiliation(s)
- L Naccache
- Unité INSERM 334, Service Hospitalier Frédéric Joliot, CEA/DRM/DSV, 4 Place du Général Leclerc, F-91401 Orsay Cedex, France.
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Dehaene S, Naccache L, Cohen L, Bihan DL, Mangin JF, Poline JB, Rivière D. Cerebral mechanisms of word masking and unconscious repetition priming. Nat Neurosci 2001; 4:752-8. [PMID: 11426233 DOI: 10.1038/89551] [Citation(s) in RCA: 789] [Impact Index Per Article: 34.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
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.
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Affiliation(s)
- S Dehaene
- Unité INSERM 334, IFR 49, Service Hospitalier Frédéric Joliot, CEA/DSV, 4 Place du Général Leclerc, 91401 Orsay cedex, France.
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Abstract
Many subliminal priming experiments are thought to demonstrate unconscious access to semantics. However, most of them can be reinterpreted in a non-semantic framework that supposes only that subjects learn to map non-semantic visual features of the subliminal stimuli onto motor responses. In order to clarify this issue, we engaged subjects in a number comparison task in which the target number was preceded by another invisible masked number. We show that unconscious semantic priming occurs even for prime stimuli that are never presented as target stimuli, and for which no stimulus-response learning could conceivably occur. We also report analyses of the impact of the numerical relation between prime and target, and of the impact of learning on priming, all of which confirm that unconscious utilization of semantic information is indeed possible.
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Affiliation(s)
- L Naccache
- Unité INSERM 334, Service Hospitalier Frédéric Joliot, CEA/DRM/DSV, 4, Place du Général Leclerc, 91401 Orsay Cedex, France.
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Pallier C, Dehaene S, Poline J, LeBihan D, Mehler J, Dupoux E. Brain imaging of language plasticity in adopted adults: can a second language replace the first? Neuroimage 2001. [DOI: 10.1016/s1053-8119(01)91925-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Affiliation(s)
- S Dehaene
- Institut National de la Santé et de la Recherche Médicale, Commisariat à l'Energie Atomique, Orsay, France.
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41
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Abstract
This introductory chapter attempts to clarify the philosophical, empirical, and theoretical bases on which a cognitive neuroscience approach to consciousness can be founded. We isolate three major empirical observations that any theory of consciousness should incorporate, namely (1) a considerable amount of processing is possible without consciousness, (2) attention is a prerequisite of consciousness, and (3) consciousness is required for some specific cognitive tasks, including those that require durable information maintenance, novel combinations of operations, or the spontaneous generation of intentional behavior. We then propose a theoretical framework that synthesizes those facts: the hypothesis of a global neuronal workspace. This framework postulates that, at any given time, many modular cerebral networks are active in parallel and process information in an unconscious manner. An information becomes conscious, however, if the neural population that represents it is mobilized by top-down attentional amplification into a brain-scale state of coherent activity that involves many neurons distributed throughout the brain. The long-distance connectivity of these 'workspace neurons' can, when they are active for a minimal duration, make the information available to a variety of processes including perceptual categorization, long-term memorization, evaluation, and intentional action. We postulate that this global availability of information through the workspace is what we subjectively experience as a conscious state. A complete theory of consciousness should explain why some cognitive and cerebral representations can be permanently or temporarily inaccessible to consciousness, what is the range of possible conscious contents, how they map onto specific cerebral circuits, and whether a generic neuronal mechanism underlies all of them. We confront the workspace model with those issues and identify novel experimental predictions. Neurophysiological, anatomical, and brain-imaging data strongly argue for a major role of prefrontal cortex, anterior cingulate, and the areas that connect to them, in creating the postulated brain-scale workspace.
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Affiliation(s)
- S Dehaene
- Unité INSERM 334, Service Hospitalier Frédéric Joliot, CEA/DRM/DSV, 4, Place du Général Leclerc, 91401 Cedex, Orsay, France.
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42
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Abstract
Neuronal network models have been proposed for the organization of evaluation and decision processes in prefrontal circuitry and their putative neuronal and molecular bases. The models all include an implementation and simulation of an elementary reward mechanism. Their central hypothesis is that tentative rules of behavior, which are coded by clusters of active neurons in prefrontal cortex, are selected or rejected based on an evaluation by this reward signal, which may be conveyed, for instance, by the mesencephalic dopaminergic neurons with which the prefrontal cortex is densely interconnected. At the molecular level, the reward signal is postulated to be a neurotransmitter such as dopamine, which exerts a global modulatory action on prefrontal synaptic efficacies, either via volume transmission or via targeted synaptic triads. Negative reinforcement has the effect of destabilizing the currently active rule-coding clusters; subsequently, spontaneous activity varies again from one cluster to another, giving the organism the chance to discover and learn a new rule. Thus, reward signals function as effective selection signals that either maintain or suppress currently active prefrontal representations as a function of their current adequacy. Simulations of this variation-selection have successfully accounted for the main features of several major tasks that depend on prefrontal cortex integrity, such as the delayed-response test, the Wisconsin card sorting test, the Tower of London test and the Stroop test. For the more complex tasks, we have found it necessary to supplement the external reward input with a second mechanism that supplies an internal reward; it consists of an auto-evaluation loop which short-circuits the reward input from the exterior. This allows for an internal evaluation of covert motor intentions without actualizing them as behaviors, by simply testing them covertly by comparison with memorized former experiences. This element of architecture gives access to enhanced rates of learning via an elementary process of internal or covert mental simulation. We have recently applied these ideas to a new model, developed with M. Kerszberg, which hypothesizes that prefrontal cortex and its reward-related connections contribute crucially to conscious effortful tasks. This model distinguishes two main computational spaces within the human brain: a unique global workspace composed of distributed and heavily interconnected neurons with long-range axons, and a set of specialized and modular perceptual, motor, memory, evaluative and attentional processors. We postulate that workspace neurons are mobilized in effortful tasks for which the specialized processors do not suffice; they selectively mobilize or suppress, through descending connections, the contribution of specific processor neurons. In the course of task performance, workspace neurons become spontaneously co-activated, forming discrete though variable spatio-temporal patterns subject to modulation by vigilance signals and to selection by reward signals. A computer simulation of the Stroop task shows workspace activation to increase during acquisition of a novel task, effortful execution, and after errors. This model makes predictions concerning the spatio-temporal activation patterns during brain imaging of cognitive tasks, particularly concerning the conditions of activation of dorsolateral prefrontal cortex and anterior cingulate, their relation to reward mechanisms, and their specific reaction during error processing.
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Affiliation(s)
- S Dehaene
- INSERM U. 334, Service Hospitalier Frédéric Joliot, CEA/DSV, Orsay, France.
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43
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Abstract
A methodology for fMRI data analysis confined to the cortex, Cortical Surface Mapping (CSM), is presented. CSM retains the flexibility of the General Linear Model based estimation, but the procedures involved are adapted to operate on the cortical surface, while avoiding to resort to explicit flattening. The methodology is tested by means of simulations and application to a real fMRI protocol. The results are compared with those obtained with a standard, volume-oriented approach (SPM), and it is shown that CSM leads to local differences in sensitivity, with generally higher sensitivity for CSM in two of the three subjects studied. The discussion provided is focused on the benefits of the introduction of anatomical information in fMRI data analysis, and the relevance of CSM as a step toward this goal.
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Affiliation(s)
- A Andrade
- Service Hospitalier Frédéric Joliot, CEA, Orsay, France
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Stanescu-Cosson R, Pinel P, van De Moortele PF, Le Bihan D, Cohen L, Dehaene S. Understanding dissociations in dyscalculia: a brain imaging study of the impact of number size on the cerebral networks for exact and approximate calculation. Brain 2000; 123 ( Pt 11):2240-55. [PMID: 11050024 DOI: 10.1093/brain/123.11.2240] [Citation(s) in RCA: 266] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Neuropsychological studies have revealed different subtypes of dyscalculia, including dissociations between exact calculation and approximation abilities, and an impact of number size on performance. To understand the origins of these effects, we measured cerebral activity with functional MRI at 3 Tesla and event-related potentials while healthy volunteers performed exact and approximate calculation tasks with small and large numbers. Bilateral intraparietal, precentral, dorsolateral and superior prefrontal regions showed greater activation during approximation, while the left inferior prefrontal cortex and the bilateral angular regions were more activated during exact calculation. Increasing number size during exact calculation led to increased activation in the same bilateral intraparietal regions as during approximation, as well the left inferior and superior frontal gyri. Event-related potentials gave access to the temporal dynamics of calculation processes, showing that effects of task and of number size could be found as early as 200-300 ms following problem presentation. Altogether, the results reveal two cerebral networks for number processing. Rote arithmetic operations with small numbers have a greater reliance on left-lateralized regions, presumably encoding numbers in verbal format. Approximation and exact calculation with large numbers, however, put heavier emphasis on the left and right parietal cortices, which may encode numbers in a non-verbal quantity format. Subtypes of dyscalculia can be explained by lesions disproportionately affecting only one of these networks.
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Affiliation(s)
- R Stanescu-Cosson
- INSERM U334, Service Hospitalier Frédéric Joliot, CEA/DSV, Orsay and Service de Neurologie 1, Hôpital de la Salpêtrière, Paris, France
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Cohen L, Dehaene S, Chochon F, Lehéricy S, Naccache L. Language and calculation within the parietal lobe: a combined cognitive, anatomical and fMRI study. Neuropsychologia 2000; 38:1426-40. [PMID: 10869586 DOI: 10.1016/s0028-3932(00)00038-5] [Citation(s) in RCA: 182] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
We report the case of a patient (ATH) who suffered from aphasia, deep dyslexia, and acalculia, following a lesion in her left perisylvian area. She showed a severe impairment in all tasks involving numbers in a verbal format, such as reading aloud, writing to dictation, or responding verbally to questions of numerical knowledge. In contrast, her ability to manipulate non-verbal representations of numbers, i.e., Arabic numerals and quantities, was comparatively well preserved, as evidenced for instance in number comparison or number bisection tasks. This dissociated impairment of verbal and non-verbal numerical abilities entailed a differential impairment of the four arithmetic operations. ATH performed much better with subtraction and addition, that can be solved on the basis of quantity manipulation, than with multiplication and division problems, that are commonly solved by retrieving stored verbal sequences. The brain lesion affected the classical language areas, but spared a subset of the left inferior parietal lobule that was active during calculation tasks, as demonstrated with functional MRI. Finally, the relative preservation of subtraction versus multiplication may be related to the fact that subtraction activated the intact right parietal lobe, while multiplication activated predominantly left-sided areas.
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Affiliation(s)
- L Cohen
- Service de Neurologie 1, Clinique Paul Castaigne, Hôpital de la Salpêtrière, Paris, France.
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Le Clec'H G, Dehaene S, Cohen L, Mehler J, Dupoux E, Poline JB, Lehéricy S, van de Moortele PF, Le Bihan D. Distinct cortical areas for names of numbers and body parts independent of language and input modality. Neuroimage 2000; 12:381-91. [PMID: 10988032 DOI: 10.1006/nimg.2000.0627] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Some models of word comprehension postulate that the processing of words presented in different modalities and languages ultimately converges toward common cerebral systems associated with semantic-level processing and that the localization of these systems may vary with the category of semantic knowledge being accessed. We used functional magnetic resonance imaging to investigate this hypothesis with two categories of words, numerals, and body parts, for which the existence of distinct category-specific areas is debated in neuropsychology. Across two experiments, one with a blocked design and the other with an event-related design, a reproducible set of left-hemispheric parietal and prefrontal areas showed greater activation during the manipulation of topographical knowledge about body parts and a right-hemispheric parietal network during the manipulation of numerical quantities. These results complement the existing neuropsychological and brain-imaging literature by suggesting that within the extensive network of bilateral parietal regions active during both number and body-part processing, a subset shows category-specific responses independent of the language and modality of presentation.
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Affiliation(s)
- G Le Clec'H
- INSERM U.334, Service Hospitalier Frédéric Joliot, CEA/DSV, 4 Place du Général Leclerc, 91401 Orsay Cedex, France
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Abstract
Recent computational models, or mathematical realizations of neurobiological theories, are providing insights into the organization and workings of the association cortex. Such models concern the construction of cortical maps, the neural basis of cognitive functions such as visual perception, reward-motivated learning and some aspects of consciousness.
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Affiliation(s)
- T Gisiger
- CNRS UA D1284 - 'Neurobiologie Moléculaire', Institut Pasteur, Paris, 75724, France
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48
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Abstract
Recent progress in the molecular biology of synaptic transmission, in particular of neurotransmitter receptors, offers novel information relevant to 'realistic' modeling of neural processes at the single cell and network level. Sophisticated computer analyses of two-dimensional crystals by high resolution electron microscopy yield images of single neurotransmitter receptor molecules with tentative identifications of ligand binding sites and of conformational transitions. The dynamics of conformational changes can be accounted for by a 'multistate allosteric network' model. Allosteric receptors also possess the structural and functional properties required to serve as coincidence detectors between pre- and post-synaptic signals and, therefore, can be used as building blocks for a chemical Hebb synapse. These properties were introduced into networks of formal neurons capable of producing and detecting temporal sequences. In more elaborate models of pre-frontal cortex functions, allosteric receptors control the selection of transient 'pre-representations' and their stabilization by external or internal reward signals. We apply this scheme to Shallice's Tower of London test, and we show how a hierarchical neuronal architecture can implement executive or planning functions associated with frontal areas. (Académie des sciences/Elsevier, Paris.)
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Affiliation(s)
- J P Changeux
- Neurobiologie moleculaire, Institu Pasteur, 25 rue du Dr Roux, 75015, Paris, France
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Cohen L, Dehaene S, Naccache L, Lehéricy S, Dehaene-Lambertz G, Hénaff MA, Michel F. The visual word form area: spatial and temporal characterization of an initial stage of reading in normal subjects and posterior split-brain patients. Brain 2000; 123 ( Pt 2):291-307. [PMID: 10648437 DOI: 10.1093/brain/123.2.291] [Citation(s) in RCA: 1167] [Impact Index Per Article: 48.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
A standard model of word reading postulates that visual information is initially processed by occipitotemporal areas contralateral to the stimulated hemifield, from whence it is subsequently transferred to the visual word form (VWF) system, a left inferior temporal region specifically devoted to the processing of letter strings. For stimuli displayed in the left visual field, this transfer proceeds from the right to the left hemisphere through the posterior portion of the corpus callosum. In order to characterize the spatial and temporal organization of these processes, reading tasks with split-field presentation were performed by five control subjects and by two patients suffering from left hemialexia following posterior callosal lesions. The subjects' responses were studied using behavioural measures and functional brain imaging techniques, providing both high spatial resolution (functional MRI, fMRI) and high temporal resolution (high-density event-related potentials, ERPs). Early visual processing was revealed as activations contralateral to stimulation, located by fMRI in the inferior occipitotemporal region and presumably coincident with area V4. A negative wave occurring 150-160 ms post-stimulus, also strictly contralateral to stimulation, was recorded over posterior electrodes. In contrast with these hemifield-dependent effects, the VWF system was revealed as a strictly left-hemispheric activation which, in control subjects, was identical for stimuli presented in the left or in the right hemifield and was located in the middle portion of the left fusiform gyrus. The electrical signature of the VWF system consisted of a unilateral sharp negativity, recorded 180-200 ms post-stimulus over left inferior temporal electrodes. In callosal patients, due to the inability of visual information to pass across the posterior part of the corpus callosum, the VWF system was activated only by stimuli presented in the right visual field. Similarly, a significant influence of the word/non-word status on ERPs recorded over the left hemisphere was discernible for either hemifield in controls, while it affected only right-hemifield stimuli in callosal patients. These findings provide direct support for the main components of the classical model of reading and help specify their timing and cerebral substrates.
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Affiliation(s)
- L Cohen
- Service de Neurologie 1, INSERM U334, Service Hospitalier Frédéric Joliot, CEA/DSV, Orsay, France.
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