New York: For the first time, scientists have found that the human brain has a "map" for perceiving numbers. Topographical maps of the human brain are known to exist for the primary senses, such as sight, hearing and touch, but this is the first time such a map has been found for numerosity, or number sense. The map's layout allows for the most efficient communication among neurons doing similar tasks, scientists said.
Studies in monkeys have shown that certain neurons in the parietal cortex, located at the back of the brain beneath the crown of the hair, became active when the animals viewed a specific number of items. These studies did not find a map for numerosity, though scientists have long suspected one exists. Researcher Ben Harvey, a neuroscientist at Utrecht University in the Netherlands, and his colleagues placed participants in a magnetic resonance imaging (MRI) scanner and showed them patterns of dots that varied in number over time.
They would show one dot over and over, then two dots over and over, then three dots, and so on, 'LiveScience' reported. The researchers used an advanced imaging method known as high-field fMRI, which allowed them to see fine-scale details of brain activity. They found the posterior parietal cortex, responded to the dot patterns in an organised way: Small numbers of dots were represented in one area, whereas large numbers were represented in another. The findings suggest that higher cognitive functions might rely on the same organisation principles as sensory systems do. In these topographical maps, a larger brain area was dedicated to perceiving smaller numbers than to larger ones, in line with previous findings that number sense becomes less precise as the quantity of items increases.
Numerosity is different from mathematical ability and only refers to numerical amount. People vary somewhat in their ability to distinguish numerosity, Harvey said. At the extreme, you have savants - individuals, many of whom have autism or a similar disorder, who possess extraordinary abilities in math, art or other areas. Some savants can look at a pile of pick-up sticks, for example, and instantly know how many there are. The study was published in the journal Science.
