Saturday science subject: Counting monkeys

— 3:53 PM on November 3, 2007

Primate brains are hard-wired for numbers, according to research quoted by the New Scientist. The publication quotes findings from Andreas Nieder and his colleagues from the University of Tübingen in Germany, who taught two rhesus monkeys to count. The monkeys were shown series of dots and Arabic numerals, and they were rewarded with cups of apple juice when they successfully matched the number of dots to given numerals. As the monkeys were doing the exercises, Nieder's team measured the activity in their brains:

Nieder and his colleagues used special probes to measure the electrical activity of individual neurons in the brains of the two primates performing this counting task for the numbers one through to four. The team focused specifically on a walnut-sized area involved in higher-level thinking, known as the prefrontal cortex.

The researchers painstakingly recorded the response rate of about 350 neurons located in each monkey's prefrontal cortex. Of the roughly 700 neurons they examined, 160 appeared to have a strong preference for a specific value between one and four.

For example, a given brain cell would send out a barrage of electrical signals whenever the animal saw three dots on the screen or the number three, but the same cell would not respond when the monkey was presented with other numerical values.

According to Liz Brannon of Duke University in Durham, North Carolina, the findings suggest non-human primates can figure out what numerals mean. "Although monkeys don't have language they can understand a symbol and what it refers to," she tells the New Scientist.

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