Addition, subtraction brain cells found in monkeys: Japan research team

TOKYO — A team of scientists in Japan recently announced the discovery of nerve cells that strongly respond to addition and subtraction in the brains of monkeys.

There is a correlation between the right hand and addition, and the left hand and subtraction, suggesting that such differences between the right and left sides may also exist in the human brain.

It is known that monkeys and chimpanzees exhibit behavior similar to humans performing addition and subtraction. While it has been believed that there are brain cells capable of performing calculations without the use of formulas or words, the details were not well understood.

The team led by neurophysiology professor Hajime Mushiake of Tohoku University conducted experiments using Japanese macaques. The animals were tasked to increase or decrease the number of white circles displayed on a monitor using handles with both hands to match the number of white circles they had memorized beforehand. The team compared the combinations of “subtracting with the right hand, adding with the left hand,” to “adding with the right hand, subtracting with the left hand.”

As a result, they found many nerve cells that strongly responded when monkeys performed addition and subtraction, and it was observed that addition cells are strongly associated with movements of the right hand, while subtraction cells are associated with movements of the left hand. The accuracy rate was the same for both combinations. The scientists believe that cells originally used for hand movements are being utilized for calculations.

Humans are said to have a sense that links addition with the right side and subtraction with the left side, such as pushing the right-hand switch to turn on electricity and turning a knob to increase the volume. The latest study has shown that this sense may be inherent in the brains of primates, rather than being influenced by culture or education. Mushiake suggests that this understanding “could potentially be applied to mathematical education based on brain function, utilizing not only numbers and symbols but also the body, such as hands and fingers.”

The team’s paper was published in the British science journal Scientific Reports on March 28.

(Japanese original by Rikka Teramachi, Lifestyle, Science & Environment News Department)