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The Journal of Neuroscience, May 30, 2007, 27(22):5986-5993; doi:10.1523/JNEUROSCI.1056-07.2007
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Behavioral/Systems/Cognitive
A Labeled-Line Code for Small and Large Numerosities in the Monkey Prefrontal Cortex
Andreas Nieder andKatharina Merten Department of Cognitive Neurology, Primate Neurocognition Laboratory, Hertie-Institute for Clinical Brain Research, University of Tuebingen, 72076 Tübingen, Germany
Correspondence should be addressed to Andreas Nieder, Primate Neurocognition Laboratory, Department of Cognitive Neurology, Hertie-Institute for Clinical Brain Research, University of Tuebingen, Otfried-Müller-Strasse 27, 72076 Tübingen, Germany. Email: andreas.nieder{at}uni-tuebingen.de
How single neurons represent information about the magnitude of a stimulus remains controversial. Neurons encoding purely sensory magnitude typically show monotonic response functions ("summation coding"), and summation units are usually implemented in models of numerosity representation. In contrast, cells representing numerical quantity exhibit nonmonotonic tuning functions that peak at their preferred numerosity ("labeled-line code"), but the restricted range of tested quantities in these studies did not permit a definite answer. Here, we analyzed both behavioral and neuronal representations of a broad range of numerosities from 1 to 30 in the prefrontal cortex of monkeys. Numerosity-selective neurons showed a clear and behaviorally relevant labeled-line code for all numerosities. Moreover, both the behavioral and neuronal tuning functions obeyed the Weber–Fechner Law and were best represented on a nonlinearly compressed scale. Our single-cell study is in good agreement with functional imaging data reporting peaked tuning functions in humans, demonstrating neuronal precursors for human number competence in a nonhuman primate. Our findings also emphasize that the manner in which neurons encode and maintain magnitude information may depend on the precise task at hand as well as the type of magnitude to represent and memorize.
Key words: monkey; number; prefrontal cortex; psychophysics; single-cell recording; neuronal coding
Received March 8, 2007; revised April 10, 2007; accepted April 25, 2007.
Correspondence should be addressed to Andreas Nieder, Primate Neurocognition Laboratory, Department of Cognitive Neurology, Hertie-Institute for Clinical Brain Research, University of Tuebingen, Otfried-Müller-Strasse 27, 72076 Tübingen, Germany. Email: andreas.nieder{at}uni-tuebingen.de
Related articles in J. Neurosci.:
- Labeled-Line Coding and Summation Coding of Numerosities in Prefrontal and Parietal Cortex
- Filip Van Opstal
J. Neurosci. 2007 27: 9535-9536.[Full Text]
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