Abstract

Non-verbal numerical competence, such as the estimation of set size, is rooted in biological primitives that can also be explored in animals. Over the past years, the anatomical substrates and neuronal mechanisms of numerical cognition in primates have been unravelled down to the level of single neurons. Studies with behaviourally-trained monkeys have identified a parietofrontal network of individual neurons selectively tuned to the number of items or the rank of items in a sequence. The properties of these neurons’ numerosity tuning curves can explain fundamental psychophysical phenomena, such as the numerical distance and size effect. Functionally overlapping groups of parietal neurons represent not only numerable-discrete quantity, but also innumerable-continuous quantity and relations between quantities, supporting the idea of a generalized magnitude system in the brain. Moreover, many neurons in the prefrontal cortex establish semantic associations between signs and abstract numerical categories, a neuronal precursor mechanisms that may ultimately give rise to symbolic number processing in humans. These studies establish putative homologies between the monkey and human brain, and demonstrate the suitability of non-human primates as model system to explore the neurobiological roots of the brain’s non-verbal quantification system, which may constitute the phylogenetic and ontogenetic foundation of all further, more elaborate numerical skills in humans.