Comparing Parietal Quantity-Processing Mechanisms between Humans and Macaques.

Quantity processing studies typically assume functional homology between regions within macaque and human intraparietal sulcus (IPS), where apparently similar locations respond to broadly similar tasks. However, macaque single cell neurophysiology is difficult to compare to human functional magnetic resonance imaging (fMRI); particularly in multivoxel pattern analysis and adaptation paradigms, or where different tasks are used. fMRI approaches incorporating neural tuning models allow closer comparison, revealing human numerosity-selective responses only outside the IPS. Extensive functional similarities support this novel homology of physical quantity processing. Human IPS instead houses a network responding to comparisons of physical quantities, symbolic numbers, and other stimulus features. This network likely reflects interactions between physical quantity processing, spatial processing, and (in humans) linguistic processing.