The article by Dehaene et al. explores the neural organization of number processing in the human brain, focusing on the parietal lobe. They propose a tripartite organization of number-related processes, involving three distinct circuits: a horizontal segment of the intraparietal sulcus (HIPS), the left angular gyrus (AG), and the posterior superior parietal system (PSPL). The HIPS is proposed to be the core quantity system, responsible for nonverbal numerical quantity manipulation, while the AG supports verbal number processing, and the PSPL contributes to attentional orientation on the mental number line. The authors review neuroimaging and neuropsychological evidence to support these proposals, highlighting the specificity of each circuit to different numerical tasks and the dissociations between operations such as addition, subtraction, and multiplication. They also discuss the developmental aspects of number processing and the potential for early deficits in number understanding, such as developmental dyscalculia.The article by Dehaene et al. explores the neural organization of number processing in the human brain, focusing on the parietal lobe. They propose a tripartite organization of number-related processes, involving three distinct circuits: a horizontal segment of the intraparietal sulcus (HIPS), the left angular gyrus (AG), and the posterior superior parietal system (PSPL). The HIPS is proposed to be the core quantity system, responsible for nonverbal numerical quantity manipulation, while the AG supports verbal number processing, and the PSPL contributes to attentional orientation on the mental number line. The authors review neuroimaging and neuropsychological evidence to support these proposals, highlighting the specificity of each circuit to different numerical tasks and the dissociations between operations such as addition, subtraction, and multiplication. They also discuss the developmental aspects of number processing and the potential for early deficits in number understanding, such as developmental dyscalculia.