Processing magnitudes within the parietal cortex

Human beings constantly process numerosity, space and duration to regulate and adapt their behaviour to the external world. It has been suggested that these fundamental adaptive abilities rely on a common magnitude processing system hosted by the parietal cortex. In this chapter, we review the many recent behavioural, lesional and brain imaging studies demonstrating functional interactions, as well as the cerebral bases underlying magnitude processing in humans and, when relevant, in monkeys. The similarities and differences between numerical, temporal and spatial estimation processes are detailed to show that separate studies of each of these magnitudes, at the behavioural, neurophysiological and neuroanatomical level, have produced convergent results, pointing to the crucial role of the parietal cortex. We also show that the links between different magnitude estimation processes, as revealed by the behavioural interactions observed during multiple-magnitude processing, rely on common populations of neurons in areas around the left and right intraparietal sulci in monkeys and in humans. By integrating all these behavioural and neurofunctional findings, we make it clear that the areas around the intraparietal sulcus host both common and partially distinct and specific representations and mechanisms for numerosity, space and duration processing. We also show how these parietal areas may interact with frontal areas of the brain to achieve these functions