The understanding of numbers and the learning of arithmetic have also been the subject of major studies in cognitive neuroscience. From the earliest age, children have an approximatenumber system ( ANS), as well as a disposition to perceive the very small numbers 1, 2, 3 ( subitizing). Numbers are part of the abstract dimensions that are perceived from birth. The intraparietal sulcus is activated very early on, particularly in the right hemisphere, and adult brain imaging shows that it contains a decodable representation of approximate numerical magnitudes. In monkeys, this region contains a population of neurons tuned to a particular number of objects, present even before any training.
Consensus exists that this "number sense", which pre-exists all learning, serves as the foundation for the acquisition of number symbols. Functional MRI demonstrates the activation of intraparietal regions as soon as an adult performs a symbolic calculation. A few rare MRI experiments in children, notably by Daniel Ansari's group, show an increase in activity with age, particularly in the left intraparietal sulcus, accompanied by a progressive refinement of quantity representation. A newly discovered region, the visualnumber formarea ( VNFA), located at the base of the inferior temporal gyrus of both hemispheres, responds to numbers written in Arabic numerals in educated adults.
