Funded Grants

The Cognitive Neuroscience of Numeracy: Exploring the cerebral substrate, the development, and the pathologies of number sens

How is word meaning represented in cerebral networks of the human brain? Although we still largely ignore how semantic knowledge can be encoded in neural tissue, research in the last decade indicates that different domains of knowledge can be selectively impaired by cerebral lesions, and that even preverbal infants possess rudimentary knowledge of specific domains such as animals, objects, or faces. This has led to the suggestion that dedicated cerebral networks are biologically predisposed to acquire knowledge of specific domains that have evolutionary significance.

Elementary arithmetic provides perhaps the clearest example of such as domain-specific biological predisposition. Animals and infants have rudimentary number knowledge with a clear analogy and continuity with the adult knowledge of arithmetic. In adults of all cultures, brain lesions of the inferior parietal region can specifically impair number sense while leaving intact knowledge of other cognitive domains. And the very same brain region is demonstrably activated during number processing. Hence, four major criteria for a domain-specific ability are fulfilled: clear evolutionary advantage to possessing the ability; presence of evolutionary precursors to the human ability; early emergence of the competence in infants independently of other abilities, including language; and existence of a dedicated cerebral substrate.

My own work has been seminal in putting together this demonstration to understand the organization of number processing in humans, I have wed most if ad an the methodologies in cognitive psychology and cognitive neuroscience including chronometric experiments in &&Its, neural network simulations, habituation-dishabituation experiments in infants ad neuropsychological and brain-imaging studies of elementary arithmetic. These studies have culminated in the definition of a model of number processing, the triple-code model, which now serves as a reference for studies of normal and impaired numerical cognition. In the most recent years, I have started testing this model using functional brain imaging techniques My work has contributed to target the inferior parietal area, in the vicinity of the intraparietal sulcus, as one of the primary circuits underlying the semantic knowledge of numbers and their interrelations. My findings have been described in over forty original publications in major scientific journals as well as in several books, including a recent general-audience book called The Number Sense, which is now published in four languages.

In the next decade, I plan to continue this work with a specific focus on how and why numbers come to be represented in a specific brain area in the course of knowledge acquisition and language development.

*Experiments will be run using functional magnetic resonance imaging (fMRI) and high-density recordings of event-related potentials (ERPS) during word processing and calculation task in adults. My colleagues and I shall compare different number processing tasks in an effort to test the triple-code model and to better understand the relative contributions of parietal, prefrontal and inferior temporal areas to mental arithmetic.

*With my wife, a psychologist and neuropediatrician who is running imaging studies of language acquisition in infancy, we shall attempt to visualize the activity of cerebral networks during the acquisition of numeracy, both in infants and in children. We shall use the available method of high-density recordings of ERPs in infants, but also hope to acquire a novel functional imaging method, near infra-red spectroscopy, to better localize the activated networks.

*In brain-lessened, retarded, or at-risk children and adults, we shall study specific how number sense is impaired and whether rehabilitation can be performed, taking advantage of the plasticity of cerebral networks. Neural modeling studies will help us understand how the acquisition of numeracy modifies the architecture of cerebral networks at the scale of single neurons and synapses. We shall also use the detailed knowledge gathered on the specific domain of number processing to address other central issues in cognitive neuroscience.

*I have designed a masked priming situation in which the numerical primes, even though they are not consciously seen, are demonstrably processed up to a semantic level and beyond. ERPs and fMRI will be used to image the networks activated by the unconscious primes, and to compare them with those activated during conscious number processing.

*Using numbers as a starting point, my research will also examine the processing of other dissociable categories of words such as animals, body parts, tools, or verbs. I shall apply a multi-disciplinary approach similar to the one used with numbers in an effort to better understand what is the logic behind the association of these categories to distinct cortical activation or lesion sites.

My project may have a broad intellectual, social, and cultural significance. At the fundamental level, it will provide an in-depth understanding of how the networks for number processing develop in infants and in young children, and how they are organized in adults as a function of task and expertise. Ideally, it might provide a prime illustration and model for how our brain represents semantic knowledge. But calculation and arithmetic are also domains of central importance to society. Dyscalculia is a frequent and poorly understood deficit in school children, with causes that range from neurological damage to an acquired phobia for mathematics. Even in children or adults who have followed a normal school curriculum, innumeracy is a growing concern. I will not neglect the possible applications of my research in the fields of developmental dyscalculia, innumeracy, their early diagnosis, and their rehabilitation. The models of number processing I am developing are already being applied by developmental psychologists such as Robbie Case to better understand normal and impaired numerical development. The cognitive tests that I am designing are also being incorporated in batteries used for the diagnosis and rehabilitation of acalculia, not only in adult, but also in younger brain-lesioned patients. Finally, the brain-imaging tools I am using and helping develop will be used to understand the normal development of the cerebral networks for arithmetic, its plasticity, and its occasional failure in at-risk populations. Ultimately, an important contribution of mathematical cognition research to society may consist in the development of novel rehabilitation and education methods with a sound scientific basis.