Despite its significance in mathematics, the way the human brain processes the number zero was previously unclear. Researchers from University Hospital Bonn (UKB), the University of Bonn, and the University of Tübingen have recently found that certain nerve cells in the medial temporal lobe treat zero as a numerical value rather than simply as “nothing.” These findings have been published in the journal Current Biology.
The number zero plays a crucial role in the evolution of numerical systems and mathematics, yet it is often viewed as one of humanity’s greatest cultural milestones. “Unlike other numbers such as one, two, or three, which denote countable quantities, zero signifies the absence of anything countable while still being a numerical value,” explains Prof. Florian Mormann, co-corresponding author and a part of the Department of Epileptology at the UKB, as well as a member of the Transdisciplinary Research Area (TRA) “Life & Health” at the University of Bonn. The notion of zero emerged relatively late in history over the last two thousand years, unlike positive whole numbers. This development is also noticeable in children’s comprehension—children typically grasp the idea of zero and relevant mathematical concepts around age six.
Nerve Cells Indicate the Number Zero
The representation of the concept of zero within human brain cells had not been thoroughly explored until now. Researchers from Bonn collaborated with neurobiologists from the University of Tübingen to investigate this issue. They presented neurosurgical patients, who had thin microelectrodes implanted in their temporal lobes at UKB for surgical preparation, with numerical values ranging from zero to nine. The numbers were displayed both as Arabic numerals and as collections of dots, including an empty set. “We were able to observe the activity of individual neurons and actually discovered cells that responded to zero,” states Esther Kutter, the study’s lead author. “These neurons reacted to either the Arabic numeral zero or the empty set, but not to both.”
For Neurons, the Number Zero Is a Numerical Value
In both scenarios, a numerical distance effect was evident; the neurons responded less strongly, though still noticeably, to the adjacent number one. “Thus, at the neuron level, the idea of zero is not represented as a separate category called ‘nothing’ but is integrated as a numerical value along with other countable numbers at the lower end of the number line,” says Prof. Dr. Andreas Nieder from the Institute of Neurobiology at the University of Tübingen. Prof. Mormann adds: “Even with this integration, the empty set is represented differently from other numbers at the neural population level, particularly regarding dot sets. This may account for the longer time it takes to recognize the empty set behaviorally, compared to other small numbers.” However, this distinction was not observed at neural or behavioral levels for Arabic numerals. The researchers emphasize the significance of symbolic representations, such as Arabic numerals, in how the brain incorporates the number zero into its numerical understanding.
