Researchers identify 'Math neurons' in brain

Does your brain fire up during additions, subtractions, and other mathematical operations? A recent study conducted by the Universities of Tubingen and Bonn showed that the brain has neurons that fired specifically during certain mathematical operations.

The findings, published in the journal 'Current Biology', indicated that some of the neurons detected were active exclusively during additions, while others were active during subtractions. They did not care whether the calculation instruction was written down as a word or a symbol.

Most elementary school children probably already know that three apples plus two apples add up to five apples. However, what happened in the brain during such calculations was still largely unknown. The current study by the Universities of Bonn and Tubingen has shed light on this issue.

The researchers benefited from a special feature of the Department of Epileptology at the University Hospital Bonn. It specialized in surgical procedures on the brains of people with epilepsy. In some patients, seizures always originated from the same area of the brain. In order to precisely localize this defective area, the doctors implanted several electrodes into the patients. The probes can be used to precisely determine the origin of the spasm. In addition, the activity of individual neurons can be measured via wiring.

Five women and four men participated in the current study. They had electrodes implanted in the so-called temporal lobe of the brain to record the activity of nerve cells. Meanwhile, the participants had to perform simple arithmetic tasks. "We found that different neurons fired during additions than during subtractions," explained Prof. Florian Mormann from the Department of Epileptology at the University Hospital Bonn.

It was not the case that some neurons responded only to a "+" sign and others only to a "-" sign: "Even when we replaced the mathematical symbols with words, the effect remained the same," explained Esther Kutter, who is doing her doctorate in Prof. Mormann's research group. "For example, when subjects were asked to calculate '5 and 3', their addition neurons sprang back into action; whereas for '7 less 4,' their subtraction neurons did."

This showed that the cells discovered actually encoded a mathematical instruction for action. The brain activity thus showed with great 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 Tubingen 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," stressed Mormann. The two teams from Bonn and Tubingen further want to investigate exactly what role the nerve cells found played in this.