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The Journal of Neuroscience, April 8, 2009, 29(14):4652-4657; doi:10.1523/JNEUROSCI.0651-09.2009

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Brief Communications
Notation-Independent Representation of Fractions in the Human Parietal Cortex

Simon N. Jacob and Andreas Nieder

Department of Animal Physiology, Institute of Neurobiology, University of Tübingen, 72076 Tübingen, Germany

Correspondence should be addressed to Andreas Nieder, Department of Animal Physiology, Institute of Neurobiology, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany. Email: andreas.nieder{at}uni-tuebingen.de

Although the concept of whole numbers is intuitive and well suited for counting and ordering, it is with the invention of fractions that the number system gained precision and flexibility. Absolute magnitude is encoded by single neurons that discharge maximally to specific numbers. However, it is unknown how the ratio of two numbers is represented, whether by processing numerator and denominator in separation, or by extending the analog magnitude code to relative quantity. Using functional MRI adaptation, we now show that populations of neurons in human fronto-parietal cortex are tuned to preferred fractions, generalizing across the format of presentation. After blood oxygen level-dependent signal adaptation to constant fractions, signal recovery to deviant fractions was modulated parametrically as a function of numerical distance between the deviant and adaptation fraction. The distance effect was invariant to changes in notation from number to word fractions and strongest in the anterior intraparietal sulcus, a key region for the processing of whole numbers. These findings demonstrate that the human brain uses the same analog magnitude code to represent both absolute and relative quantity. Our results have implications for mathematical education, which may be tailored to better harness our ability to access automatically a composite quantitative measure.

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Received Feb. 8, 2009; accepted March 9, 2009.

Correspondence should be addressed to Andreas Nieder, Department of Animal Physiology, Institute of Neurobiology, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany. Email: andreas.nieder{at}uni-tuebingen.de

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