"Accumulator Neurons" Necessary For Counting Objects

Main Category: Neurology / Neuroscience
Also Included In: Biology / Biochemistry
Article Date: 25 Jul 2007 - 9:00 PDT

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As any child knows, to answer the question "how many," one must start by adding up individual objects in a group. This cognitive ability is shared by animals as diverse as humans and birds. Surprisingly, the exact brain mechanisms responsible for this process remained unknown until now. This week in the online open-access journal PLoS Biology, Jamie Roitman, Elizabeth Brannon, and Michael Platt from the University of Illinois at Chicago report novel evidence for the existence of "accumulator neurons," which respond to increasing numbers of items in a display with progressively increasing activity, in the parietal cortex of monkeys.

The authors focused on the parietal cortex based on evidence that damage to this brain region disrupts basic mathematical skills, and is activated during functional imaging studies when people perform basic computations. To understand how parietal cortex contributes to numerical behavior, the authors studied the activity of neurons in the lateral intraparietal area in monkeys while they looked at arrays of dots on a computer screen. Parietal neurons responded with progressively increasing activity as the total number of elements in the display was varied across a wide range of values (2-32). These neurons resemble "accumulator neurons" that have been suggested to serve the first stage in counting. This information could be used by other neurons that respond best for a particular cardinal number, such as "4," as have been reported in prior studies. These findings support computer models that separate the processes of summing and numerical identification, and may also explain the fact that parietal cortex damage causes both numerical and spatial confusion.

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Citation: Roitman JD, Brannon EM, Platt ML (2007) Monotonic coding of numerosity in macaque lateral intraparietal area. PLoS Biol 5(8): e208. doi:10.1371/journal.pbio. 0050208.

CONTACT:
Jamie Roitman
University of Illinois at Chicago
MC 285
1007 W Harrison St
Chicago, IL 60607

SOURCE: THE OPEN-ACCESS JOURNAL PLoS BIOLOGY (http://www.plosbiology.org/) .

All works published in PLoS Biology are open access. Everything is immediately available -- to read, download, redistribute, include in databases, and otherwise use -- without cost to anyone, anywhere, subject only to the condition that the original authorship and source are properly attributed. Copyright is retained by the authors. The Public Library of Science uses the Creative Commons Attribution License.

Source: Natalie Bouaravong
Public Library of Science

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