Neuronal correlates of a visual “sense of number” in primate parietal and prefrontal cortices
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Edited by Charles Gross, Princeton University, Princeton, NJ, and approved May 21, 2013 (received for review April 30, 2013)

Abstract
“Sense of number” refers to the classical idea that we perceive the number of items (numerosity) intuitively. However, whether the brain signals numerosity spontaneously, in the absence of learning, remains unknown; therefore, we recorded from neurons in the ventral intraparietal sulcus and the dorsolateral prefrontal cortex of numerically naive monkeys. Neurons in both brain areas responded maximally to a given number of items, showing tuning to a preferred numerosity. Numerosity was encoded earlier in area ventral intraparietal area, suggesting that numerical information is conveyed from the parietal to the frontal lobe. Visual numerosity is thus spontaneously represented as a perceptual category in a dedicated parietofrontal network. This network may form the biological foundation of a spontaneous number sense, allowing primates to intuitively estimate the number of visual items.
Footnotes
- ↵1To whom correspondence should be addressed. E-mail: andreas.nieder{at}uni-tuebingen.de.
Author contributions: P.V. and A.N. designed research; P.V. performed research; A.N. contributed new reagents/analytic tools; P.V. analyzed data; and P.V. and A.N. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.