By carefully analyzing brain activity, scientists can tell what number a person has just seen, research now reveals.
They can similarly tell how many dots a person was presented with.
Past investigations had uncovered brain cells in monkeys that were linked with numbers. Although scientists had found brain regions linked with numerical tasks in humans — the frontal and parietal lobes, to be exact — until now patterns of brain activity linked with specific numbers had proven elusive.
Scientists had 10 volunteers watch either numerals or dots on a screen while a part of their brain known as the intraparietal cortex was scanned — it's a region of the parietal lobe especially linked with numbers. They next rigorously analyzed brain activity to decipher which patterns might be linked with the numbers the volunteers had observed.
When it came to small numbers of dots, the researchers found that brain activity patterns changed gradually in a way that reflected the ordered nature of the numbers. For example, one might be able to conclude that the pattern for six is between that for five and seven.
In the case of the numerals, the researchers could not detect this same gradual change. This suggests their methods simply might not be sensitive enough to detect this progression yet, or that these symbols are in fact coded as more precise, discrete entities in the brain.
"Activation patterns for numbers of dots seem to be stronger — are more easily discriminated — than those for digits, suggesting that maybe still more neurons encode specifically numbers of objects — the evolutionary older representation — than abstract symbolic numbers," said researcher Evelyn Eger at the University of Paris-Sud in Orsay, France.
Given that numbers "are in principle infinite, it is very unlikely that the brain can have, or we can detect, a signature for each number," Eger noted. "There is some hint in our data that smaller numbers have a clearer signature, which may be related to their frequency of occurrence in daily life, but further work would be needed to say something more definite about this and about how the brain deals with larger numbers."
The methods employed in this research could ultimately help unlock how the brain makes sophisticated calculations and how the brain changes as people learn math, the researchers said.
"We are only beginning to access the most basic building blocks that symbolic math probably relies on," Eger said. "We still have no clear idea of how these number representations interact and are combined in mathematical operations, but the fact that we can resolve them in humans gives hope that at some point we can come up with paradigms that let us address this.”
The scientists detailed their findings online September 24 in the journal Current Biology.
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