Representation of Numerical Information in the Brain

Abstract

Numbers can be used most flexibly to quantify and rank. Cardinal number refers to quantitative number assignments assessing set size (numerosity), whereas ordinal number applies to numerical rank that concerns serial order. Behavioural studies in animals, human infants and innumerate adults have demonstrated that numerical competence does not emerge de novo in linguistic humans, but builds up on biological precursor systems. Single-cell recordings in monkeys as well as functional imaging studies in humans showed that quantity information is represented in the posterior parietal cortex in close association with the prefrontal cortex. The response properties of numerosity-selective cortical cells can explain basic psychophysical phenomena, such as the numerical distance effect and the numerical size effect. In humans, the intra-parietal sulcus of the parietal lobe is specifically activated by non-verbal and verbal quantity information, independent of sensory modality, symbolic notation or cognitive status. Numerical rank irrespective of the sensory properties of objects is encoded by neurons in the lateral prefrontal cortex of monkeys. Neurons that encode the ordinal position of task-related hand or eye movements have been found in a variety of motor-related cortical areas in trained monkeys. Prefrontal in addition to parietal cortices have also been found to be more strongly activated for order information in human functional imaging studies. Together, neural data on numerosity and serial order indicate that numerical quantity and rank order information are likely to share the same neural system, with the prefrontal cortex and the intra-parietal sulcus as key structures.