Sex differences in number processing: Differential systems for subtraction and multiplication were confirmed in men, but not in women

Belinda Pletzer

doi:10.1038/srep39064

Abstract

Neuroimaging studies suggest segregated neuronal systems underlying number magnitude processing (e.g. subtraction) and arithmetic fact retrieval (e.g. multiplication). While number magnitude processing is thought to rely on the intraparietal sulcus (IPS) bilaterally, arithmetic fact retrieval is thought to rely on the left angular gyrus (AG). However, evidence from brain damaged patients and brain stimulation challenges this view and suggests considerable overlap between the systems underlying number magnitude processing and arithmetic fact retrieval. This study investigates, whether sex differences in number processing can account for these conflicting findings. A subtraction and a multiplication task were administered to 40 men and 34 women in their luteal phase during functional MRI. Replicating previous studies in men, we found the IPS to be more strongly activated during subtraction than multiplication, and the AG to be more strongly activated during multiplication than subtraction. However, no differences between the two tasks were observed in women.

Highlights

The triple-code model of number processing[1] suggests segregated neuronal systems for the processing of number magnitudes and the retrieval of arithmetic facts
A specific impairment of multiplication fact retrieval has been reported in cases without lesions to the left AG/SMG, whereas preserved multiplication performance was observed in a patient with severe lesions to the left AG/SMG10,11
In order to confirm the borrowing and distance effects reported in the literature and evaluate sex differences on subtraction performance, 2 × 2 × 2 mixed ANOVAs with the within-subject factors ‘borrowing’ and ‘distance’ and the between subjects factor ‘sex’ were performed on both reaction times (RT) and error rates (ER)

Summary

Introduction

The triple-code model of number processing[1] suggests segregated neuronal systems for the processing of number magnitudes (e.g. subtraction or number comparison) and the retrieval of arithmetic facts, (e.g. single digit addition and multiplication). Results from studies using different numerical tasks for number magnitude processing and arithmetic fact retrieval Non-multiplicative compared to multiplicative items lead to increased BOLD-response in the IPS. Multiplicative compared to non-multiplicative items lead to increased BOLD-response in the left AG. The IPS is a prominent activation site during spatial processing e.g.4,5, while the AG is involved in verbal and memory processing e.g.6 These shared activation sites as well as behavioural evidence led to the assumption, that number magnitudes have a spatial representation[7], and arithmetic fact retrieval is verbally mediated[1]. Further support for the notion that number magnitude processing and arithmetic fact retrieval rely on dissociated neural systems comes from studies on brain damaged patients. In brain stimulation studies, parts of the left AG and IPS were identified www.nature.com/scientificreports/

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