During calculations, some neurons are active during addition, others during subtraction

The brain has neurons that fire specifically during certain mathematical operations. This is shown by a recent study carried out by the universities of Tübingen and Bonn. The results indicate that some of the detected neurons are active exclusively during additions, while others are active during subtractions. They don’t care whether the calculation instruction is written as a word or a symbol. The results have just been published in the journal current biology.

Most elementary school kids probably already know that three apples plus two apples makes five apples. However, what happens in the brain during such calculations is still largely unknown. The ongoing study by the universities of Bonn and Tübingen now sheds light on this question.

The researchers benefited from a special feature of the epileptology department of the University Hospital of Bonn. He specializes in brain surgery for people with epilepsy. In some patients, the seizures always come from the same area of ​​the brain. In order to precisely locate this defective area, doctors implant several electrodes on patients. Probes can be used to precisely determine the origin of the spasm. Additionally, the activity of individual neurons can be measured via wiring.

Some neurons only fire on summation

Five women and four men participated in this study. They had electrodes implanted in the so-called temporal lobe of the brain to record nerve cell activity. During this time, participants had to perform simple arithmetic tasks. “We found that different neurons were activated during additions than during subtractions,” explains Professor Florian Mormann from the Department of Epileptology at the University Hospital Bonn.

It was not true that some neurons only responded to a “+” sign and others only to a “-” sign: “Even when we replaced the mathematical symbols with words, the effect remained the same “, explains Esther Kutter, who is doing her doctorate in Professor Mormann’s research group. “For example, when subjects were asked to calculate ‘5 plus 3’, their addition neurons kicked in, whereas for ‘7 minus 4’, their subtraction neurons did. .”

This shows that the discovered cells actually encode a mathematical instruction for the action. The brain activity thus showed with great precision the type of tasks that the test subjects were currently calculating: the researchers fed the activity patterns of the cells 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 learning phase, it was able to identify precisely during which calculation operation it had been recorded.

Professor Andreas Nieder from the University of Tübingen supervised the study together with Professor Mormann. “We know from experiments with monkeys that neurons specific to certain calculation rules also exist in their brains,” he says. “In humans, however, there are virtually no 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. Here too, the researchers found nerve cells that were activated specifically during addition or subtraction. However, during summation, different addition neurons became active alternately during the same arithmetic task. Figuratively speaking, it is as if the plus key on the calculator is constantly changing its location. It was the same with subtraction. Researchers also call this “dynamic coding”.

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

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

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Material provided by University of Bonn. Note: Content may be edited for style and length.

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