Publications of year 2007
  1. Stanislas Dehaene. Les neurones de la lecture. Odile Jacob, 2007. [bibtex-entry]

  1. Susannah Kyle Revkin. Investigating the processes involved in subitizing and numerical estimation: a study of healthy and brain-damaged subjects. PhD thesis, 2007. [PDF] [bibtex-entry]

Book chapters
  1. Stanislas Dehaene. Conscious and non-conscious processes: Distinct forms of evidence accumulation?, chapter 2, pages 1-29. 2007. [PDF] [bibtex-entry]

  2. Stanislas Dehaene, Véronique Izard, Catherine Lemer, and Pierre Pica. Quels sont les liens entre arithmétique et langage? Une étude en Amazonie. In J. Bricmont and J. J. Franck, editors,Chomsky, pages 188--196. L'Herne, 2007. [PDF] [bibtex-entry]

  3. Stanislas Dehaene. Symbols and quantities in parietal cortex: elements of a mathematical theory of number representation and manipulation. In Patrick Haggard, Yves Rossetti, and Mitsuo Kawato, editors,Sensorimotor foundations of higher cognition, volume XXII of Attention and Performance, chapter 24, pages 527-574. Harvard University Press, 2007. [PDF] [bibtex-entry]

  4. Rosalie Footnick. A hidden language: Recovery of a 'lost' language is triggered by hypnosis. In Merel Keijzer Barbara Köpke, Monika S. Schmid and Susan Dostert, editors,Language Attrition: Theoretical perspectives. John Benjamins, Amsterdam. 2007. [PDF] [bibtex-entry]

  5. Christophe Pallier. Critical periods in language acquisition and language attrition. In Barbara Köpke, Monika S. Schmid, Merel Keijzer, and Susan Dostert, editors,Language Attrition: Theoretical perspectives. John Benjamins, Amsterdam, 2007. [PDF] [bibtex-entry]

  6. Jean-Baptiste Poline, Ferath Kherif, Christophe Pallier, and Will Penny. Contrasts and Classical Inference. In Karl Friston, editor,Statistical Parameter Mapping. Elsevier, 2007. [bibtex-entry]

  7. Anna Juliet Wilson and Stanislas Dehaene. Number sense and developmental dyscalculia. In Donna Coch, Geraldine Dawson, and Kurt Fischer, editors,Human behavior, learning and the developing brain: Atypical development. Guilford Press, New York, 2007. [PDF]
    Abstract: In this chapter we review the possible biological bases for developmental dyscalculia, which is a disorder in mathematical abilities presumed to be due to impaired brain function. By reviewing what is known about the localization of numerical cognition functions in the adult brain, the causes of acquired dyscalculia, and the normal development of numerical cognition, we propose several hypotheses for causes of developmental dyscalculia, including that of a core deficit of "number sense" related to an impairment in the horizontal intra- parietal sulcus (HIPS) area. We then discuss research on dyscalculia, including the contribution of recent imaging results in special populations, and evaluate to what extent this research supports our hypotheses. We conclude that there is promising preliminary evidence for a core deficit of number sense in dyscalculia, but we also emphasize that more research is needed to test the hypothesis of multiple types of dyscalculia, particularly in the area of dyscalculia subtyping. We complete the chapter with a discussion of future directions to be taken, the implications for education, and the construction of number sense remediation software in our laboratory

Articles in journals
  1. Marco Buiatti, David Papo, Pierre-Marie Baudonniere, and Carl van Vreeswijk. Feedback modulates the temporal scale-free dynamics of brain electrical activity in a hypothesis testing task. Neuroscience, 146:1400-12, 2007. [PDF] [bibtex-entry]

  2. Stanislas Dehaene. A few steps toward a science of mental life. Mind, Brain, and Education, 1, 2007. [PDF] [bibtex-entry]

  3. Stanislas Dehaene and Laurent Cohen. Response to Carreiras et al: The role of visual similarity, feedforward, feedback and lateral pathways in reading. Trends Cogn Sci, 11(11):456--457, November 2007. [WWW] [PDF] [bibtex-entry]

  4. Stanislas Dehaene and Laurent Cohen. Cultural recycling of cortical maps. Neuron, 56(2):384--398, October 2007. [WWW] [PDF]
    Abstract: Part of human cortex is specialized for cultural domains such as reading and arithmetic, whose invention is too recent to have influenced the evolution of our species. Representations of letter strings and of numbers occupy reproducible locations within large-scale macromaps, respectively in the left occipito-temporal and bilateral intraparietal cortex. Furthermore, recent fMRI studies reveal a systematic architecture within these areas. To explain this paradoxical cerebral invariance of cultural maps, we propose a neuronal recycling hypothesis, according to which cultural inventions invade evolutionarily older brain circuits and inherit many of their structural constraints

  5. Antoine Del Cul, Sylvain Baillet, and Stanislas Dehaene. Brain dynamics underlying the nonlinear threshold for access to consciousness. PLoS Biol, 5(10):e260, October 2007. [WWW] [PDF]
    Abstract: When a flashed stimulus is followed by a backward mask, subjects fail to perceive it unless the target-mask interval exceeds a threshold duration of about 50 ms. Models of conscious access postulate that this threshold is associated with the time needed to establish sustained activity in recurrent cortical loops, but the brain areas involved and their timing remain debated. We used high-density recordings of event-related potentials (ERPs) and cortical source reconstruction to assess the time course of human brain activity evoked by masked stimuli and to determine neural events during which brain activity correlates with conscious reports. Target-mask stimulus onset asynchrony (SOA) was varied in small steps, allowing us to ask which ERP events show the characteristic nonlinear dependence with SOA seen in subjective and objective reports. The results separate distinct stages in mask-target interactions, indicating that a considerable amount of subliminal processing can occur early on in the occipito-temporal pathway (<250 ms) and pointing to a late (>270 ms) and highly distributed fronto-parieto-temporal activation as a correlate of conscious reportability

  6. Ansgar D Endress, Ghislaine Dehaene-Lambertz, and Jacques Mehler. Perceptual constraints and the learnability of simple grammars.. Cognition, 105(3):577--614, December 2007. [WWW]
    Abstract: Cognitive processes are often attributed to statistical or symbolic general-purpose mechanisms. Here we show that some spontaneous generalizations are driven by specialized, highly constrained symbolic operations. We explore how two types of artificial grammars are acquired, one based on repetitions and the other on characteristic relations between tones ("ordinal" grammars). Whereas participants readily acquire repetition-based grammars, displaying early electrophysiological responses to grammar violations, they perform poorly with ordinal grammars, displaying no such electrophysiological responses. This outcome is problematic for both general symbolic and statistical models, which predict that both types of grammars should be processed equally easily. This suggests that some simple grammars are acquired using perceptual primitives rather than general-purpose mechanisms; such primitives may be elements of a "toolbox" of specialized computational heuristics, which may ultimately allow constructing a psychological theory of symbol manipulation.

  7. Raphaël Gaillard, Laurent Cohen, Claude Adam, Stéphane Clemenceau, Dominique Hasboun, Michel Baulac, Jean-Claude Willer, Stanislas Dehaene, and Lionel Naccache. Subliminal words durably affect neuronal activity. Neuroreport, 18(15):1527--1531, October 2007. [WWW] [PDF]
    Abstract: Unconscious mental representations elicited by subliminal stimuli are marked by their fleeting lifetimes, usually below 1 s. Can such evanescent subliminal stimuli, nevertheless, lead to long-lasting learning? To date, evidence suggesting a long-term influence of briefly perceived stimuli on behaviour or brain activity is scarce and questionable. In this study, we used intracranial recordings to provide the first direct demonstration that unconsciously perceived subliminal words could exert long-lasting effects on neuronal signals. When repeating subliminal words over long interstimulus intervals, we observed electrophysiological repetition effects. These unconscious repetition effects suggest that the single presentation of a masked word can durably affect neural architecture

  8. Anne-Lise Giraud, Andreas Kleinschmidt, David Poeppel, Torben E Lund, Richard S J Frackowiak, and Helmut Laufs. Endogenous cortical rhythms determine cerebral specialization for speech perception and production. Neuron, 56(6):1127--1134, December 2007. [WWW] [PDF]
    Abstract: Across multiple timescales, acoustic regularities of speech match rhythmic properties of both the auditory and motor systems. Syllabic rate corresponds to natural jaw-associated oscillatory rhythms, and phonemic length could reflect endogenous oscillatory auditory cortical properties. Hemispheric lateralization for speech could result from an asymmetry of cortical tuning, with left and right auditory areas differentially sensitive to spectro-temporal features of speech. Using simultaneous electroencephalographic (EEG) and functional magnetic resonance imaging (fMRI) recordings from humans, we show that spontaneous EEG power variations within the gamma range (phonemic rate) correlate best with left auditory cortical synaptic activity, while fluctuations within the theta range correlate best with that in the right. Power fluctuations in both ranges correlate with activity in the mouth premotor region, indicating coupling between temporal properties of speech perception and production. These data show that endogenous cortical rhythms provide temporal and spatial constraints on the neuronal mechanisms underlying speech perception and production

  9. Narly Golestani, Nicolas Molko, Stanislas Dehaene, Denis Lebihan, and Christophe Pallier. Brain structure predicts the learning of foreign speech sounds. Cereb Cortex, 17(3):575--582, March 2007. [WWW] [PDF]
    Abstract: Previous work has shown a relationship between parietal lobe anatomy and nonnative speech sound learning. We scanned a new group of phonetic learners using structural magnetic resonance imaging and diffusion tensor imaging. Voxel-based morphometry indicated higher white matter (WM) density in left Heschl's gyrus (HG) in faster compared with slower learners, and manual segmentation of this structure confirmed that the WM volume of left HG is larger in the former compared with the latter group. This finding was replicated in a reanalysis of the original groups tested in Golestani and others (2002, Anatomical correlates of learning novel speech sounds. Neuron 35:997-1010). We also found that faster learners have a greater asymmetry (left > right) in parietal lobe volumes than slower learners and that the right insula and HG are more superiorly located in slower compared with faster learners. These results suggest that left auditory cortex WM anatomy, which likely reflects auditory processing efficiency, partly predicts individual differences in an aspect of language learning that relies on rapid temporal processing. It also appears that a global displacement of components of a right hemispheric language network, possibly reflecting individual differences in the functional anatomy and lateralization of language processing, is predictive of speech sound learning

  10. Narly Golestani and Christophe Pallier. Anatomical correlates of foreign speech sound production. Cereb Cortex, 17(4):929--934, April 2007. [WWW] [PDF]
    Abstract: Previous work has shown a relationship between brain anatomy and how quickly adults learn to perceive foreign speech sounds. Faster learners have greater asymmetry (left > right) in parietal lobe white matter (WM) volumes and larger WM volumes of left Heschl's gyrus than slower learners. Here, we tested native French speakers who were previously scanned using high-resolution anatomical magnetic resonance imaging. We asked them to pronounce a Persian consonant that does not exist in French but which can easily be distinguished from French speech sounds, the voiced uvular stop. Two judges scored the goodness of the utterances. Voxel-based morphometry revealed that individuals who more accurately pronounce the foreign sound have higher WM density in the left insula/prefrontal cortex and in the inferior parietal cortices bilaterally compared with poorer producers. Results suggest that WM anatomy in brain regions previously implicated in articulation and phonological working memory, or the size/shape of these or adjacent regions, is in part predictive of the accuracy of speech sound pronunciation

  11. Grit Hein, Arjen Alink, Andreas Kleinschmidt, and Notger G Müller. Competing neural responses for auditory and visual decisions. PLoS ONE, 2:e320, 2007. [WWW] [PDF]
    Abstract: Why is it hard to divide attention between dissimilar activities, such as reading and listening to a conversation? We used functional magnetic resonance imaging (fMRI) to study interference between simple auditory and visual decisions, independently of motor competition. Overlapping activity for auditory and visual tasks performed in isolation was found in lateral prefrontal regions, middle temporal cortex and parietal cortex. When the visual stimulus occurred during the processing of the tone, its activation in prefrontal and middle temporal cortex was suppressed. Additionally, reduced activity was seen in modality-specific visual cortex. These results paralleled impaired awareness of the visual event. Even without competing motor responses, a simple auditory decision interferes with visual processing on different neural levels, including prefrontal cortex, middle temporal cortex and visual regions

  12. Edward M Hubbard. Neurophysiology of synesthesia.. Curr Psychiatry Rep, 9(3):193--199, June 2007. [PDF]
    Abstract: Synesthesia is an experience in which stimulation in one sensory or cognitive stream leads to associated experiences in a second, unstimulated stream. Although synesthesia is often referred to as a "neurological condition," it is not listed in the DSM IV or the ICD classifications, as it generally does not interfere with normal daily functioning. However, its high prevalence rate (one in 23) means that synesthesia may be reported by patients who present with other psychiatric symptoms. In this review, I focus on recent research examining the neural basis of the two most intensively studied forms of synesthesia, grapheme --> color synesthesia and tone --> color synesthesia. These data suggest that these forms of synesthesia are elicited through anomalous activation of color-selective areas, perhaps in concert with hyperbinding mediated by the parietal cortex. I then turn to questions for future research and the implications of these models for other forms of synesthesia.

  13. Andreas Kleinschmidt. Incidental neuroimaging findings: lessons from brain research in volunteers. Curr Opin Neurol, 20(4):387--389, August 2007. [WWW] [PDF] [bibtex-entry]

  14. Andreas Kleinschmidt. Different analysis solutions for different spatial resolutions? Moving towards a mesoscopic mapping of functional architecture in the human brain. Neuroimage, 38(4):663--665, December 2007. [WWW] [PDF]
    Abstract: This comment challenges the dichtotomy that Kriegeskorte and Bandettini (this issue) propose to exist between "activation-based" and "information-based" approaches to fMRI analyses and argues that multi-variate analyses are just a special case within the overall repertoire of methods for analyzing paradigm-related BOLD signal variations. Moreover, this comment argues that using multi-variate approaches comes at a price, trading-off spatial resolution for sensitivity, and thus partially cancels potential benefits from high-field fMRI. Paradoxically, this comment thus concludes that pattern analyses provide a powerful complement to existing methods but not the complement that will actually permit to map functional architecture at mesoscopic resolution, i.e., one of the most interesting applications of high-field fMRI

  15. Sid Kouider, Stanislas Dehaene, Antoinette Jobert, and Denis Le Bihan. Cerebral bases of subliminal and supraliminal priming during reading.. Cereb Cortex, 17(9):2019--2029, September 2007. [WWW] [PDF]
    Abstract: Several studies have investigated the neural correlates of conscious perception by contrasting functional magnetic resonance imaging (fMRI) activation to conscious and nonconscious visual stimuli. The results often reveal an amplification of posterior occipito-temporal activation and its extension into a parieto-frontal network. However, some of these effects might be due to a greater deployment of attentional or strategical processes in the conscious condition. Here, we examined the brain activity evoked by visible and invisible stimuli, both of which were irrelevant to the task. We collected fMRI data in a masking paradigm in which subliminal versus supraliminal letter strings were presented as primes while subjects focused attention on another subsequent, highly visible target word. Under those conditions, prime visibility was associated with greater activity confined to bilateral posterior occipito-temporal cortices, without extension into frontal and parietal cortices. However, supraliminal primes, compared with subliminal primes, evoked more extensive repetition suppression in a widely distributed set of parieto-frontal areas. Furthermore, only supraliminal primes caused phonological repetition enhancement in left inferior frontal and anterior insular cortex. Those results suggest a 2-stage view of conscious access: Relative to masked stimuli, unmasked stimuli elicit increased occipito-temporal activity, thus allowing them to compete for global conscious access and to induce priming in multiple distant areas. In the absence of attention, however, their access to a second stage of distributed parieto-frontal processing may remain blocked.

  16. Sid Kouider and Stanislas Dehaene. Levels of processing during non-conscious perception: a critical review of visual masking. Philos Trans R Soc Lond B Biol Sci, 362(1481):857--875, May 2007. [WWW] [PDF]
    Abstract: Understanding the extent and limits of non-conscious processing is an important step on the road to a thorough understanding of the cognitive and cerebral correlates of conscious perception. In this article, we present a critical review of research on subliminal perception during masking and other related experimental conditions. Although initially controversial, the possibility that a broad variety of processes can be activated by a non-reportable stimulus is now well established. Behavioural findings of subliminal priming indicate that a masked word or digit can have an influence on perceptual, lexical and semantic levels, while neuroimaging directly visualizes the brain activation that it evokes in several cortical areas. This activation is often attenuated under subliminal presentation conditions compared to consciously reportable conditions, but there are sufficiently many exceptions, in paradigms such as the attentional blink, to indicate that high activation, per se, is not a sufficient condition for conscious access to occur. We conclude by arguing that for a stimulus to reach consciousness, two factors are jointly needed: (i) the input stimulus must have enough strength (which can be prevented by masking) and (ii) it must receive top-down attention (which can be prevented by drawing attention to another stimulus or task). This view leads to a distinction between two types of non-conscious processes, which we call subliminal and preconscious. According to us, maintaining this distinction is essential in order to make sense of the growing neuroimaging data on the neural correlates of consciousness

  17. Claire Landmann, Stanislas Dehaene, Sabina Pappata, Antoinette Jobert, Michel Bottlaender, Dimitri Roumenov, and Denis Le Bihan. Dynamics of Prefrontal and Cingulate Activity during a Reward-Based Logical Deduction Task. Cereb Cortex, 17:749-759, 2007. [WWW] [PDF]
    Abstract: We used behavioral and functional magnetic resonance imaging (fMRI) methods to probe the cerebral organization of a simple logical deduction process. Subjects were engaged in a motor trial-and-error learning task, in which they had to infer the identity of an unknown 4-key code. The design of the task allowed subjects to base their inferences not only on the feedback they received but also on the internal deductions that it afforded (autoevaluation). fMRI analysis revealed a large bilateral parietal, prefrontal, cingulate, and striatal network that activated suddenly during search periods and collapsed during ensuing periods of sequence repetition. Fine-grained analyses of the temporal dynamics of this search network indicated that it operates according to near-optimal rules that include 1) computation of the difference between expected and obtained rewards and 2) anticipatory deductions that predate the actual reception of positive reward. In summary, the dynamics of effortful mental deduction can be tracked with fMRI and relate to a distributed network engaging prefrontal cortex and its interconnected cortical and subcortical regions

  18. Koleen McCrink, Stanislas Dehaene, and Ghislaine Dehaene-Lambertz. Moving along the number line: operational momentum in nonsymbolic arithmetic. Perception & Psychophysics, 69(8):1324--1333, November 2007. [PDF]
    Abstract: Can human adults perform arithmetic operations with large approximate numbers, and what effect, if any, does an internal spatial-numerical representation of numerical magnitude have on their responses? We conducted a psychophysical study in which subjects viewed several hundred short videos of sets of objects being added or subtracted from one another and judged whether the final numerosity was correct or incorrect. Over a wide range of possible outcomes, the subjects' responses peaked at the approximate location of the true numerical outcome and gradually tapered off as a function of the ratio of the true and proposed outcomes (Weber's law). Furthermore, an operational momentum effect was observed, whereby addition problems were overestimated and subtraction problems were underestimated. The results show that approximate arithmetic operates according to precise quantitative rules, perhaps analogous to those characterizing movement on an internal continuum

  19. Notger G Müller and Andreas Kleinschmidt. Temporal dynamics of the attentional spotlight: neuronal correlates of attentional capture and inhibition of return in early visual cortex. J Cogn Neurosci, 19(4):587--593, April 2007. [WWW] [PDF]
    Abstract: A stimulus that suddenly appears in the corner of the eye inevitably captures our attention, and this in turn leads to faster detection of a second stimulus presented at the same position shortly thereafter. After about 250 msec, however, this effect reverses and the second stimulus is detected faster when it appears far away from the first. Here, we report a potential physiological correlate of this time-dependent attentional facilitation and inhibition. We measured the activity in visual cortex representations of the second (target) stimulus' location depending on the stimulus onset asynchrony (SOA) and spatial distance that separated the target from the preceding cue stimulus. At an SOA of 100 msec, the target yielded larger responses when it was presented near to than far away from the cue. At an SOA of 850 msec, however, the response to the target was more pronounced when it appeared far away from the cue. Our data show how the neural substrate of visual orienting is guided by immediately preceding sensory experience and how a fast-reacting brain system modulates sensory processing by briefly increasing and subsequently decreasing responsiveness in parts of the visual cortex. We propose these activity modulations as the neural correlate of the sequence of perceptual facilitation and inhibition after attentional capture

  20. Kimihiro Nakamura, Stanislas Dehaene, Antoinette Jobert, Denis Le Bihan, and Sid Kouider. Task-specific change of unconscious neural priming in the cerebral language network.. Proc Natl Acad Sci U S A, 104(49):19643--19648, December 2007. [WWW] [PDF]
    Abstract: We explored the impact of task context on subliminal neural priming using functional magnetic resonance imaging. The repetition of words during semantic categorization produced activation reduction in the left middle temporal gyrus previously associated with semantic-level representation and dorsal premotor cortex. By contrast, reading aloud produced repetition enhancement in the left inferior parietal lobe associated with print-to-sound conversion and ventral premotor cortex. Analyses of effective connectivity revealed that the task set for reading generated reciprocal excitatory connections between the left inferior parietal and superior temporal regions, reflecting the audiovisual integration required for vocalization, whereas categorization did not produce such backward projection to posterior regions. Thus, masked repetition priming involves two distinct components in the task-specific neural streams, one in the parietotemporal cortex for task-specific word processing and the other in the premotor cortex for behavioral response preparation. The top-down influence of task sets further changes the directions of the unconscious priming in the entire cerebral circuitry for reading.

  21. Boris New, Marc Brysbaert, Jean Veronis, and Christophe Pallier. The use of film subtitles to estimate word frequencies. Applied Psycholinguistics, 28:661-677, 2007. [PDF] [bibtex-entry]

  22. Manuela Piazza, Philippe Pinel, Denis Le Bihan, and Stanislas Dehaene. A Magnitude Code Common to Numerosities and Number Symbols in Human Intraparietal Cortex. Neuron, 53(2):293--305, January 2007. [WWW] [PDF]
    Abstract: Activation of the horizontal segment of the intraparietal sulcus (hIPS) has been observed in various number-processing tasks, whether numbers were conveyed by symbolic numerals (digits, number words) or by nonsymbolic displays (dot patterns). This suggests an abstract coding of numerical magnitude. Here, we critically tested this hypothesis using fMRI adaptation to demonstrate notation-independent coding of numerical quantity in the hIPS. Once subjects were adapted either to dot patterns or to Arabic digits, activation in the hIPS and in frontal regions recovered in a distance-dependent fashion whenever a new number was presented, irrespective of notation changes. This remained unchanged when analyzing the hIPS peaks from an independent localizer scan of mental calculation. These results suggest an abstract coding of approximate number common to dots, digits, and number words. They support the idea that symbols acquire meaning by linking neural populations coding symbol shapes to those holding nonsymbolic representations of quantities

  23. Philippe Pinel, Bertrand Thirion, Sébastien Meriaux, Antoinette Jobert, Julien Serres, Denis Le Bihan, Jean-Baptiste Poline, and Stanislas Dehaene. Fast reproducible identification and large-scale databasing of individual functional cognitive networks.. BMC Neurosci, 8:91, 2007. [WWW] [PDF]
    Abstract: BACKGROUND: Although cognitive processes such as reading and calculation are associated with reproducible cerebral networks, inter-individual variability is considerable. Understanding the origins of this variability will require the elaboration of large multimodal databases compiling behavioral, anatomical, genetic and functional neuroimaging data over hundreds of subjects. With this goal in mind, we designed a simple and fast acquisition procedure based on a 5-minute functional magnetic resonance imaging (fMRI) sequence that can be run as easily and as systematically as an anatomical scan, and is therefore used in every subject undergoing fMRI in our laboratory. This protocol captures the cerebral bases of auditory and visual perception, motor actions, reading, language comprehension and mental calculation at an individual level. RESULTS: 81 subjects were successfully scanned. Before describing inter-individual variability, we demonstrated in the present study the reliability of individual functional data obtained with this short protocol. Considering the anatomical variability, we then needed to correctly describe individual functional networks in a voxel-free space. We applied then non-voxel based methods that automatically extract main features of individual patterns of activation: group analyses performed on these individual data not only converge to those reported with a more conventional voxel-based random effect analysis, but also keep information concerning variance in location and degrees of activation across subjects. CONCLUSION: This collection of individual fMRI data will help to describe the cerebral inter-subject variability of the correlates of some language, calculation and sensorimotor tasks. In association with demographic, anatomical, behavioral and genetic data, this protocol will serve as the cornerstone to establish a hybrid database of hundreds of subjects suitable to study the range and causes of variation in the cerebral bases of numerous mental processes.

  24. C. Poupon, F. Poupon, A. Roche, Y. Cointepas, J. Dubois, and J. F. Mangin. Real-time MR diffusion tensor and Q-ball imaging using Kalman filtering.. Med Image Comput Comput Assist Interv Int Conf Med Image Comput Comput Assist Interv, 10(Pt 1):27--35, 2007.
    Abstract: Magnetic resonance diffusion imaging (dMRI) has become an established research tool for the investigation of tissue structure and orientation. In this paper, we present a method for real time processing of diffusion tensor and Q-ball imaging. The basic idea is to use Kalman filtering framework to fit either the linear tensor or Q-ball model. Because the Kalman filter is designed to be an incremental algorithm, it naturally enables updating the model estimate after the acquisition of any new diffusion-weighted volume. Processing diffusion models and maps during ongoing scans provides a new useful tool for clinicians, especially when it is not possible to predict how long a subject may remain still in the magnet.

  25. Françoise Reuter, Antoine Del Cul, Bertrand Audoin, Irina Malikova, Lionel Naccache, Jean Philippe Ranjeva, Olivier Lyon-Caen, André Ali Chérif, Laurent Cohen, Stanislas Dehaene, and Jean Pelletier. Intact subliminal processing and delayed conscious access in multiple sclerosis. Neuropsychologia, 45:2683-91, April 2007. [WWW] [PDF]
    Abstract: Periventricular white matter damage affecting large bundles connecting distant cortical areas may constitute the main neuronal mechanism for the deficit of controlled information processing observed in patients with early multiple sclerosis (MS). Visual backward masking has been demonstrated to affect late stages of conscious perception involving long-range interactions between visual perceptual areas and higher level integrative cortices while leaving intact early feed-forward visual processing and even complex processing such as object recognition or semantic processing. We therefore hypothesized that patients with early MS would have an elevated masking threshold, because of an impairment of conscious perception whereas subliminal processing of masked stimuli would be preserved. Twenty-two patients with early MS and 22 normal controls performed two backward-masking experiments. We used Arabic digits as stimuli and varied quasi-continuously the temporal interval with a subsequent mask, thus allowing us to progressively "unmask" the stimuli. We finely quantified the visibility of the masked stimuli using both objective and subjective measures, thus obtaining accurate estimates of the threshold duration for access to consciousness. We also studied the priming effect caused by the variably masked numbers on a comparison task performed on a subsequently presented and highly visible target number. The threshold for access to consciousness of masked stimuli was elevated in MS patients compared to controls, whereas non-conscious processing of these stimuli, as measured by priming, was preserved. These findings suggest that conscious access to masked stimuli depends on the integrity of large-scale cortical integrative processes, which involve long-distance white matter projections, and are impaired due to diffuse demyelinating injury in patients with early MS

  26. S. Rodrigo, Catherine Oppenheim, F. Chassoux, Narly Golestani, Yann Cointepas, Cyrille Poupon, Franck Semah, Jean-François Mangin, Denis Le Bihan, and J-F. Meder. Uncinate fasciculus fiber tracking in mesial temporal lobe epilepsy. Initial findings. Eur Radiol, January 2007. [WWW]
    Abstract: In temporal lobe epilepsy (TLE) due to hippocampal sclerosis (HS), ictal discharge spread to the frontal and insulo-perisylvian cortex is commonly observed. The implication of white matter pathways in this propagation has not been investigated. We compared diffusion tensor imaging (DTI) measurements along the uncinate fasciculus (UF), a major tract connecting the frontal and temporal lobes, in patients and controls. Ten right-handed patients referred for intractable TLE due to a right HS were investigated on a 1.5-T MR scanner including a DTI sequence. All patients had interictal fluorodeoxyglucose PET showing an ipsilateral temporal hypometabolism associated with insular and frontal or perisylvian hypometabolism. The controls consisted of ten right-handed healthy subjects. UF fiber tracking was performed, and its fractional anisotropy (FA) values were compared between patients and controls, separately for the right and left UF. The left-minus-right FA UF asymmetry index was computed to test for intergroup differences. Asymmetries were found in the control group with right-greater-than-left FA. This asymmetrical pattern was lost in the patient group. Right FA values were lower in patients with right HS versus controls. Although preliminary, these findings may be related to the preferential pathway of seizure spread from the mesial temporal lobe to frontal and insulo-perisylvian areas

  27. M. Sigman, A. Jobert, D. Lebihan, and Stanislas Dehaene. Parsing a sequence of brain activations at psychological times using fMRI. Neuroimage, 35(2):655--668, April 2007. [WWW] [PDF]
    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

  28. Philipp Sterzer and Andreas Kleinschmidt. A neural basis for inference in perceptual ambiguity. Proc Natl Acad Sci U S A, 104(1):323--328, January 2007. [WWW] [PDF]
    Abstract: When looking at ambiguous visual stimuli, the observer experiences frequent spontaneous transitions between two competing percepts while physical stimulation remains unchanged. Despite recent advances in understanding the neural processes underlying such perceptual rivalry, a key question has remained unresolved: Does perceptual rivalry result merely from local bistability of neural activity patterns in sensory stimulus representations, or do higher-order areas play a causal role by shifting inference and, thus, initiating perceptual changes? We used functional MRI to measure brain activity while human observers reported successive spontaneous changes in perceived direction for an ambiguous apparent motion stimulus. In a control condition, the individual sequences of spontaneous perceptual switches during bistability were replayed by using a disambiguated version of the stimulus. Greater activations during spontaneous compared with stimulus-driven switches were observed in inferior frontal cortex bilaterally. Subsequent chronometric analyses of event-related signal time courses showed that, relative to activations in motion-sensitive extrastriate visual cortex, right inferior frontal cortex activation occurred earlier during spontaneous than during stimulus-driven perceptual changes. The temporal precedence of right inferior frontal activations suggests that this region participates in initiating spontaneous switches in perception during constant physical stimulation. Our findings can thus be seen as a signature of when and where the brain "makes up its mind" about competing perceptual interpretations of a given sensory input pattern

  29. Philipp Sterzer, Christina Stadler, Fritz Poustka, and Andreas Kleinschmidt. A structural neural deficit in adolescents with conduct disorder and its association with lack of empathy. Neuroimage, 37(1):335--342, August 2007. [WWW] [PDF]
    Abstract: The goal of this study was to determine whether brain regions implicated in emotion processing show structural alterations in adolescents with conduct disorder (CD). Using an optimized voxel-based morphometry protocol, we compared grey matter volume in 12 patients with CD and 12 age-, sex-, and intelligence-matched control subjects. Grey matter volume in bilateral anterior insular cortex and the left amygdala was significantly reduced in CD patients compared to healthy control subjects. The insular grey matter abnormalities could be attributed to aggressive behaviour. Moreover, bilateral anterior insular grey matter volume in CD patients correlated significantly with empathy scores. These novel findings point at a joint neuroanatomical substrate underpinning aggressive behaviour and impaired capacity of empathy and suggest a critical role for the anterior insula in regulating social behaviour

  30. Bertrand Thirion, Philippe Pinel, Sébastien Mériaux, Alexis Roche, Stanislas Dehaene, and Jean-Baptiste Poline. Analysis of a large fMRI cohort: Statistical and methodological issues for group analyses. Neuroimage, 35(1):105--120, March 2007. [WWW] [PDF]
    Abstract: The aim of group fMRI studies is to relate contrasts of tasks or stimuli to regional brain activity increases. These studies typically involve 10 to 16 subjects. The average regional activity statistical significance is assessed using the subject to subject variability of the effect (random effects analyses). Because of the relatively small number of subjects included, the sensitivity and reliability of these analyses is questionable and hard to investigate. In this work, we use a very large number of subject (more than 80) to investigate this issue. We take advantage of this large cohort to study the statistical properties of the inter-subject activity and focus on the notion of reproducibility by bootstrapping. We asked simple but important methodological questions: Is there, from the point of view of reliability, an optimal statistical threshold for activity maps? How many subjects should be included in group studies? What method should be preferred for inference? Our results suggest that i) optimal thresholds can indeed be found, and are rather lower than usual corrected for multiple comparison thresholds, ii) 20 subjects or more should be included in functional neuroimaging studies in order to have sufficient reliability, iii) non-parametric significance assessment should be preferred to parametric methods, iv) cluster-level thresholding is more reliable than voxel-based thresholding, and v) mixed effects tests are much more reliable than random effects tests. Moreover, our study shows that inter-subject variability plays a prominent role in the relatively low sensitivity and reliability of group studies

  31. Fabien Vinckier, Stanislas Dehaene, Antoinette Jobert, Jean Philippe Dubus, Mariano Sigman, and Laurent Cohen. Hierarchical coding of letter strings in the ventral stream: dissecting the inner organization of the visual word-form system. Neuron, 55(1):143--156, July 2007. [WWW] [PDF]
    Abstract: Visual word recognition has been proposed to rely on a hierarchy of increasingly complex neuronal detectors, from individual letters to bigrams and morphemes. We used fMRI to test whether such a hierarchy is present in the left occipitotemporal cortex, at the site of the visual word-form area, and with an anterior-to-posterior progression. We exposed adult readers to (1) false-font strings; (2) strings of infrequent letters; (3) strings of frequent letters but rare bigrams; (4) strings with frequent bigrams but rare quadrigrams; (5) strings with frequent quadrigrams; (6) real words. A gradient of selectivity was observed through the entire span of the occipitotemporal cortex, with activation becoming more selective for higher-level stimuli toward the anterior fusiform region. A similar gradient was also seen in left inferior frontoinsular cortex. Those gradients were asymmetrical in favor of the left hemisphere. We conclude that the left occipitotemporal visual word-form area, far from being a homogeneous structure, presents a high degree of functional and spatial hierarchical organization which must result from a tuning process during reading acquisition



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