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Specific “mathematical neurons” found in the brain

When performing calculations, some neurons are active in addition, others – in subtraction.

There are neurons in the brain that are triggered during certain mathematical operations. This is shown by a recent study conducted by the Universities of Tübingen and Bonn. The results show that some of the detected neurons are active exclusively during addition, and others are active during subtraction. They don’t care if the instructions are written in words or symbols. Now the results are published in the journal Modern biology.

Most elementary school kids probably already know that three apples plus two apples add up to five apples. However, what happens in the brain during such calculations is still largely unknown. The current study, conducted by the Universities of Bonn and Tübingen, now sheds light on this issue.

The activity of neurons in the brain

Some neurons in the brain become active specifically when performing addition tasks, others – when subtracting. Credit: Christian Burkert / Folkswagen-Stiftung / University of Bonn

The researchers took advantage of a feature of the epilepsy department at Bono University Hospital. She specializes in brain surgery for people with epilepsy. In some patients, seizures always occur from the same area of ​​the brain. To accurately locate this defective site, doctors implant several electrodes in patients. Probes can be used to accurately determine the origin of the spasm. In addition, the activity of individual neurons can be measured using wiring.

Some neurons only work when summing up

The current study involved five women and four men. Electrodes to record the activity of nerve cells were implanted in the so-called temporal lobe of the brain. Meanwhile, participants had to perform simple arithmetic tasks. “We found that different neurons were triggered during addition than during subtraction,” explains Professor Florian Morman of the Epileptology Department at Bona University Hospital.

It was not the case that some neurons responded only to the “+” sign and others only to the “-” sign: “Even if we replaced the mathematical symbols with words, the effect remained the same,” explains Esther Cutter, who is doing her doctorate in a research group. Professor Morman. “For example, when subjects were asked to calculate“ 5 and 3, ”their additional neurons returned to action; whereas for “7 less than 4” their subtraction neurons did. “

Tiny electrodes implanted in the brain

For the study, tiny electrodes were implanted in the brains of five women and four men to measure the activity of individual neurons. Credit: Christian Burkert / Folkswagen-Stiftung / University of Bonn

This shows that the detected cells actually encode mathematical instructions for action. Brain activity thus proved to be excellent[{” attribute=””>accuracy what kind of tasks the test subjects were currently calculating: The researchers fed the cells’ activity patterns into a self-learning computer program. At the same time, they told the software whether the subjects were currently calculating a sum or a difference. When the algorithm was confronted with new activity data after this training phase, it was able to accurately identify during which computational operation it had been recorded.

Prof. Andreas Nieder from the University of Tübingen supervised the study together with Prof. Mormann. “We know from experiments with monkeys that neurons specific to certain computational rules also exist in their brains,” he says. “In humans, however, there is hardly any data in this regard.” During their analysis, the two working groups came across an interesting phenomenon: One of the brain regions studied was the so-called parahippocampal cortex. There, too, the researchers found nerve cells that fired specifically during addition or subtraction. However, when summing up, different addition neurons became alternately active during one and the same arithmetic task. Figuratively speaking, it is as if the plus key on the calculator were constantly changing its location. It was the same with subtraction. Researchers also refer to this as “dynamic coding.”

“This study marks an important step towards a better understanding of one of our most important symbolic abilities, namely calculating with numbers,” stresses Mormann. The two teams from Bonn and Tübingen now want to investigate exactly what role the nerve cells found play in this.

Reference: “Neuronal codes for arithmetic rule processing in the human brain” by Esther F. Kutter, Jan Boström, Christian E. Elger, Andreas Nieder and Florian Mormann, 14 February 2022, Current Biology.
DOI: 10.1016/j.cub.2022.01.054

The study was funded by the German Research Foundation (DFG) and the Volkswagen Foundation.



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