Role of distinct parietal areas in arithmetic: An fMRI-guided TMS study

• Published in: NeuroImage (Orlando, Fla.) Fla.), 2011-02, Vol.54 (4), p.3048-3056
• Main Authors: Andres, Michael, Pelgrims, Barbara, Michaux, Nicolas, Olivier, Etienne, Pesenti, Mauro
• Format: Article
• Language: English
• Subjects: Brain; Brain Mapping; Calculation; Cognition - physiology; Humans; Language; Magnetic Resonance Imaging; Magnitude; Male; Mathematical Concepts; Medical imaging; Multiplication & division; Parietal Lobe - physiology; Procedure; Retrieval; Semantic; Studies; Transcranial Magnetic Stimulation; Young Adult
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2010.11.009

Although several parietal areas are known to be involved in number processing, their possible role in arithmetic operations remains debated. It has been hypothesized that the horizontal segment of the intraparietal sulcus (hIPS) and the posterior superior parietal lobule (PSPL) contribute to operations solved by calculation procedures, such as subtraction, but whether these areas are also involved in operations solved by memory retrieval, such as multiplication, is controversial. In the present study, we first identified the parietal areas involved in subtraction and multiplication by means of functional magnetic resonance imaging (fMRI) and we found an increased activation, bilaterally, in the hIPS and PSPL during both arithmetic operations. In order to test whether these areas are causally involved in subtraction and multiplication, we used transcranial magnetic stimulation (TMS) to create, in each participant, a virtual lesion of either the hIPS or PSPL, over the sites corresponding to the peaks of activation gathered in fMRI. When compared to a control site, we found an increase in response latencies in both operations after a virtual lesion of either the left or right hIPS, but not of the PSPL. Moreover, TMS over the hIPS increased the error rate in the multiplication task. The present results indicate that even operations solved by memory retrieval, such as multiplication, rely on the hIPS. In contrast, the PSPL seems to underlie processes that are nonessential to solve basic subtraction and multiplication problems. ►fMRI was used to identify the areas activated during subtraction and multiplication. ►TMS was used to test the causal relationship between these areas and each operation. ►The hIPS contributes to the solving of both subtraction and multiplication problems. ►The PSPL is not crucial to solve basic arithmetic problems.