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‘Math neurons’ have been discovered in the brain

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Some neurons are active while adding, whereas others are active when subtracting when conducting arithmetic.

Neurons in the brain fire in a certain pattern during certain mathematical calculations. According to the results, some of the neurons found are only active during additions, while others are only active during subtractions. Whether the computation command is expressed as a word or a symbol, they answer in the same way.

Neurons in the brain fire in a certain pattern during certain mathematical calculations. A new research undertaken by the Universities of Tübingen and Bonn confirms this. According to the results, some of the neurons found are only active during additions, while others are only active during subtractions. It makes no difference to them whether the computation instruction is written in words or symbols. The findings have just been published in Current Biology.

Most primary school students are familiar with the fact that three apples plus two apples equals five apples. However, little is known about what occurs in the brain during such computations. The present research conducted by the Universities of Bonn and Tübingen throws light on this topic.

The researchers took use of a unique characteristic of the University Hospital Bonn’s Department of Epileptology. It specializes in surgical operations on epilepsy patients’ brains. Seizures in certain people always come from the same part of the brain. The physicians implant many electrodes into the patients in order to properly locate the faulty location. The probes may be used to pinpoint the exact location of the spasm. Furthermore, the wiring may be used to assess the activity of individual neurons.

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Only while summing up do some neurons activate

The present research included five women and four males. Electrodes were inserted in the so-called temporal lobe of the brain to record nerve cell activity. In the meanwhile, the participants were required to complete easy arithmetic exercises. “We discovered that distinct neurons responded during additions and subtractions,” says Prof. Florian Mormann of the University Hospital Bonn’s Department of Epileptology.

It wasn’t the case that certain neurons only reacted to the “+” sign while others only responded to the “-” sign: “The impact remained the same even when we substituted the mathematical symbols with English,” says Esther Kutter, a doctoral student in Prof. Mormann’s study group. “When individuals were asked to calculate ‘5 and 3,’ their addition neurons reactivated; when they were asked to calculate ‘7 less 4,’ their subtraction neurons reactivated.”

This demonstrates that the cells identified represent a mathematical command for action. The test respondents’ brain activity therefore revealed with high precision what tasks they were now calculating: The activity patterns of the cells were supplied into a self-learning computer software by the researchers. They also informed the program whether the individuals were computing a sum or a difference at the moment. After this training phase, when the system was presented with fresh activity data, it was able to reliably identify the computing task it had been captured during.

Prof. Andreas Nieder of the University of Tübingen, in collaboration with Prof. Mormann, oversaw the research. “Experiments with monkeys have shown that neurons specialized to certain computational rules exist in their brains,” he explains. “However, there is very little data about humans in this aspect.” During their investigation, the two working groups discovered a fascinating phenomenon: The so-called parahippocampal cortex was one of the brain areas investigated. The researchers also discovered nerve cells that activated just during addition or subtraction. During one and the same arithmetic exercise, however, various addition neurons were alternately active while summing up. In a metaphorical sense, it’s as if the addition key on the calculator was continually shifting its position. Subtraction was the same way. This is also known as “dynamic coding” by researchers.

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“This research is an essential step toward a deeper understanding of one of our most important symbolic talents, namely number calculation,” says Mormann. The two teams from Bonn and Tübingen now aim to find out more about the nerve cells they discovered.

The German Research Foundation (DFG) and the Volkswagen Foundation financed the research.

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