​Since his birth, Man has possessed fundamental capacities for digitization inherited from his evolution, which gives him the ability to do elaborate mathematics. Number processing in humans is multifaceted and its ability to estimate the number of objects in a visual scene or solve a mental arithmetic problem requires neuronal activation within the human parietal cortex. Scientists have detected, at the level of the intra-parietal sulcus, neuronal circuits organized in such a way as to process numbers.
However, it is still unclear whether it is the same region that is activated or whether there are specific sub-regions for different aspects of digital processing? The low spatial resolution and volume averaging obtained in subjects having performed conventional fMRI scans at lower magnetic fields do not allow to establish an exact relationship between the observed activation and specific sub-regions.
Neurospin researchers acquired high-resolution (7 Tesla) fMRI data in 16 healthy volunteers and analyzed the neuronal activations that occur during the performance of various tasks involving number perception or numerical operations in relation to anatomical and functional landmarks on the cortical surface (Figure). The results reveal that the intra-parietal sulcus is heterogeneous: its upper/medial part responds preferentially to the visual processing of concrete sets of objects, while the lateral/lower part is recruited during mental operations (such as calculation and quantitative comparison). The first of these regions coincides with a series of representations of the visual field and could be equivalent to the regions dealing with object counts in non-human primates, while the second appears to be a distinct and potentially human-specific region.

These results improve our understanding of how number processing operates in the general organization of the human parietal cortex. The methodological approach used here is promising and can be applied to other areas of cognition as well.