Coding of numerical quantity in the primate brain,
with special reference to zero.
Institute of Neurobiology, Dept. of Biology, University of Tübingen, Germany
Findings in animal cognition, developmental psychology and anthropology indicate that the ability to deal with numbers is rooted in nonverbal biological primitives. Humans and non-human primates share an elemental quantification system that resides in a dedicated neural network in the parietal and frontal lobes. In this cortical network, ‘number neurons’ encode the number of elements in a set, its ‘numerosity’, irrespective of stimulus appearance across sensory-motor systems, and from both spatial and temporal presentation arrays. While the coding of the number of items in a set is already abstract and demanding, representing empty sets, ‘nothing’, as a relevant and quantitative category is even more challenging. For that reason, the empty set and the zero are latecomers both in human history and ontogeny. I will argue that precursors of zero are already present in the behavior and neuronal responses of nonhuman primates. Our single-neuron data suggest a parieto-frontal processing hierarchy along which empty sets are steadily detached from visual properties and gradually positioned in a numerical continuum. These findings elucidate not only how the brain encodes the quantity of countable items, but also how it transforms ‘nothing’ into an abstract quantitative category, ‘zero’.